This changes struct objfile to use a gdb_bfd_ref_ptr. In addition to
removing some manual memory management, this fixes a use-after-free
that was introduced by the registry rewrite series. The issue there
was that, in some cases, registry shutdown could refer to memory that
had already been freed. This help fix the bug by delaying the
destruction of the BFD reference (and thus the per-bfd object) until
after the registry has been shut down.
When we need to evaluate a DWARF expression in order to resolve some
dynamic property of a type we call the dwarf2_evaluate_property
function, which is declared in gdb/dwarf/loc.h and defined in
gdb/dwarf/loc.c.
Currently, this function takes (amongst other things) an argument of
type property_addr_info called addr_stack and a boolean called
push_initial_value. When push_initial_value then the top value of
addr_stack is pushed onto the dwarf expression evaluation stack before
the expression is evaluated.
So far this has worked fine, as the only two cases we needed to handle
are the case the DWARF expression doesn't require the object
address (what the top of addr_stack represents), and the case where
the DWARF expression does require the address.
In the next commit this is going to change. As we add support for
Fortran assumed rank arrays, we need to start resolving the dynamic
properties of arrays. To do this, we need to push the array rank onto
the dwarf expression evaluation stack before the expression is
evaluated.
This commit is a refactoring commit aimed at making it easier to
support Fortran assumed rank arrays. Instead of passing a boolean,
and using this to decide if we should push the object address or not,
we instead pass an array (view) of values that should be pushed to the
dwarf expression evaluation stack.
In the couple of places where we previously passed push_initial_value
as true (mostly this was defaulting to false), we now have to pass the
address from the addr_stack as an item in the array view.
In the next commit, when we want to handle passing the array rank,
this will easily be supported too.
There should be no user visible changes after this commit.
While examining the dwarf expression evaluator, I noticed that in
dwarf2_locexpr_baton_eval, whenever push_initial_value is true, the
addr_stack will never be nullptr.
This allows for a small cleanup, replacing an if/then/else with an
assertion.
There should be no user visible changes after this commit.
Now that filtered and unfiltered output can be treated identically, we
can unify the printf family of functions. This is done under the name
"gdb_printf". Most of this patch was written by script.
Now that filtered and unfiltered output can be treated identically, we
can unify the putc family of functions. This is done under the name
"gdb_putc". Most of this patch was written by script.
Now that filtered and unfiltered output can be treated identically, we
can unify the puts family of functions. This is done under the name
"gdb_puts". Most of this patch was written by script.
A large customer program has a function that is partitioned into hot
and cold parts. A variable in a callee of this function is described
using DW_OP_GNU_entry_value, but gdb gets confused when trying to find
the caller. I tracked this down to dwarf2_get_pc_bounds interpreting
the function's changes so that the returned low PC is the "wrong"
function.
Intead, when processing DW_TAG_call_site, the low PC of each range in
DW_AT_ranges should be preserved in the call_site_target. This fixes
the variable lookup in the test case I have.
I didn't write a standalone test for this as it seemed excessively
complicated.
In order to handle the case where a call site target might refer to
multiple addresses, we change the code to use a callback style. Any
spot using call_site_target::address now passes in a callback function
that may be called multiple times.
call_site_find_chain_1 has a comment claiming that recursive calls
would be too expensive. However, I doubt this is so expensive; and
furthermore the explicit state management approach here is difficult
both to understand and to modify. This patch changes this code to use
explicit recursion, so that a subsequent patch can generalize this
code without undue trauma.
Additionally, I think this patch detects a latent bug in the recursion
code. (It's hard for me to be completely certain.) The bug is that
when a new target_call_site is entered, the code does:
if (target_call_site)
{
if (addr_hash.insert (target_call_site->pc ()).second)
{
/* Successfully entered TARGET_CALL_SITE. */
chain.push_back (target_call_site);
break;
}
}
Here, if entering the target_call_site fails, then any tail_call_next
elements in this call site are not visited. However, if this code
does happen to enter a call site, then the tail_call_next elements
will be visited during backtracking. This applies when doing the
backtracking as well -- it will only continue through a given chain as
long as each element in the chain can successfully be visited.
I'd appreciate some review of this. If this behavior is intentional,
it can be added to the new implementation.
While investigating this bug, I wasn't sure if chain_candidate might
update 'chain'. I changed it to accept a const reference, making it
clear that it cannot. This simplifies the code a tiny bit as well.
This makes the data members of call_site_target 'private'. This lets
us remove most of its public API. call_site_to_target_addr is changed
to be a method of this type. This is a preparatory refactoring for
the fix at the end of this series.
call_site_target reuses field_loc_kind and field_location. However,
it has never used the full range of the field_loc_kind enum. In a
subsequent patch, I plan to add a new 'kind' here, so it seemed best
to avoid this reuse and instead introduce new types here.
Add a getter and a setter for a symbol's type. Remove the corresponding
macro and adjust all callers.
Change-Id: Ie1a137744c5bfe1df4d4f9ae5541c5299577c8de
Add a getter and a setter for a compunit_symtab's block line section. Remove
the corresponding macro and adjust all callers.
Change-Id: I3eb1a323388ad55eae8bfa45f5bc4a08dc3df455
This commit brings all the changes made by running gdb/copyright.py
as per GDB's Start of New Year Procedure.
For the avoidance of doubt, all changes in this commits were
performed by the script.
Simon pointed out that my recent patches to .debug_loclists caused
some regressions. After a brief discussion we realized it was because
his system compiler defaults to PIE.
This patch changes this code to unconditionally apply the text offset
here. It also changes loclist_describe_location to work more like
dwarf2_find_location_expression.
I tested this by running the gdb.dwarf2 tests both with and without
-pie.
When the code to handle DW_LLE_start_end was added (as part of some
DWARF 5 work), it was written to add the base address. However, this
seems incorrect -- the DWARF standard describes this as an address,
not an offset from the base address.
This patch changes a couple of spots in dwarf2/loc.c to fix this
problem. It then changes decode_debug_loc_addresses to return
DEBUG_LOC_OFFSET_PAIR instead, which preserves the previous semantics.
This only showed up on the RISC-V target internally, due to the
combination of DWARF 5 and a newer version of GCC. I've updated a
couple of existing loclists test cases to demonstrate the bug.
The bug fixed by this [1] patch was caused by an out-of-bounds access to
a value's content. The code gets the value's content (just a pointer)
and then indexes it with a non-sensical index.
This made me think of changing functions that return value contents to
return array_views instead of a plain pointer. This has the advantage
that when GDB is built with _GLIBCXX_DEBUG, accesses to the array_view
are checked, making bugs more apparent / easier to find.
This patch changes the return types of these functions, and updates
callers to call .data() on the result, meaning it's not changing
anything in practice. Additional work will be needed (which can be done
little by little) to make callers propagate the use of array_view and
reap the benefits.
[1] https://sourceware.org/pipermail/gdb-patches/2021-September/182306.html
Change-Id: I5151f888f169e1c36abe2cbc57620110673816f3
This adds an is_optimized_out function pointer to lval_funcs, and
changes value_optimized_out to call it. This new function lets gdb
determine if a value is optimized out without necessarily fetching the
value. This is needed for a subsequent patch, where an attempt to
access a lazy value would fail due to the value size limit -- however,
the access was only needed to determine the optimized-out state.
Consider test-case gdb.trace/entry-values.exp with target board
unix/-fPIE/-pie.
Using this command we have an abbreviated version, and can see the correct
@entry values for foo:
...
$ gdb -q -batch outputs/gdb.trace/entry-values/entry-values \
-ex start \
-ex "break foo" \
-ex "set print entry-values both" \
-ex continue
Temporary breakpoint 1 at 0x679
Temporary breakpoint 1, 0x0000555555554679 in main ()
Breakpoint 2 at 0x55555555463e
Breakpoint 2, 0x000055555555463e in foo (i=0, i@entry=2, j=2, j@entry=3)
...
Now, let's try the same again, but run directly to foo rather than stopping at
main:
...
$ gdb -q -batch outputs/gdb.trace/entry-values/entry-values \
-ex "break foo" \
-ex "set print entry-values both" \
-ex run
Breakpoint 1 at 0x63e
Breakpoint 1, 0x000055555555463e in foo (i=0, i@entry=<optimized out>, \
j=2, j@entry=<optimized out>)
...
So, what explains the difference? Noteworthy, this is a dwarf assembly
test-case, with debug info for foo and bar, but not for main.
In the first case:
- we run to main
- this does not trigger expanding debug info, because there's none for main
- we set a breakpoint at foo
- this triggers expanding debug info. Relocated addresses are used in
call_site info (because the exec is started)
- we continue to foo, and manage to find the call_site info
In the second case:
- we set a breakpoint at foo
- this triggers expanding debug info. Unrelocated addresses are used in
call_site info (because the exec is not started)
- we run to foo
- this triggers objfile_relocate1, but it doesn't update the call_site
info addresses
- we don't manage to find the call_site info
We could fix this by adding the missing call_site relocation in
objfile_relocate1.
This solution however is counter-trend in the sense that we're trying to
work towards the situation where when starting two instances of an executable,
we need only one instance of debug information, implying the use of
unrelocated addresses.
So, fix this instead by using unrelocated addresses in call_site info.
Tested on x86_64-linux.
This fixes all remaining unix/-fno-PIE/-no-pie vs unix/-fPIE/-pie
regressions, like f.i. PR24892.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24892
Co-Authored-By: Tom de Vries <tdevries@suse.de>
There are cases where the result of the expression evaluation is
expected to be in a form of a value and not location description.
One place that has this requirement is dwarf_entry_parameter_to_value
function, but more are expected in the future. Until now, this
requirement was fulfilled by extending the evaluated expression with
a DW_OP_stack_value operation at the end.
New implementation, introduces a new evaluation argument instead.
* dwarf2/expr.c (dwarf_expr_context::fetch_result): Add as_lval
argument.
(dwarf_expr_context::eval_exp): Add as_lval argument.
* dwarf2/expr.h (struct dwarf_expr_context): Add as_lval
argument to fetch_result and eval_exp methods.
* dwarf2/frame.c (execute_stack_op): Add as_lval argument.
* dwarf2/loc.c (dwarf_entry_parameter_to_value): Remove
DWARF expression extension.
(dwarf2_evaluate_loc_desc_full): Add as_lval argument support.
(dwarf2_evaluate_loc_desc): Add as_lval argument support.
(dwarf2_locexpr_baton_eval): Add as_lval argument support.
Idea of this patch is to get a clean and simple public interface for
the dwarf_expr_context class, looking like:
- constructor,
- destructor,
- push_address method and
- evaluate method.
Where constructor should only ever require a target architecture
information. This information is held in per object file
(dwarf2_per_objfile) structure, so it makes sense to keep that
structure as a constructor argument. It also makes sense to get the
address size from that structure, but unfortunately that interface
doesn't exist at the moment, so the dwarf_expr_context class user
needs to provide that information.
The push_address method is used to push a CORE_ADDR as a value on
top of the DWARF stack before the evaluation. This method can be
later changed to push any struct value object on the stack.
The evaluate method is the method that evaluates a DWARF expression
and provides the evaluation result, in a form of a single struct
value object that describes a location. To do this, the method requires
a context of the evaluation, as well as expected result type
information. If the type information is not provided, the DWARF generic
type will be used instead.
To avoid storing the gdbarch information in the evaluator object, that
information is now always acquired from the per_objfile object.
All data members are now private and only visible to the evaluator
class, so a m_ prefix was added to all of their names to reflect that.
To make this distinction clear, they are also accessed through objects
this pointer, wherever that was not the case before.
gdb/ChangeLog:
* dwarf2/expr.c (dwarf_expr_context::dwarf_expr_context): Add
address size argument.
(dwarf_expr_context::read_mem): Change to use property_addr_info
structure.
(dwarf_expr_context::evaluate): New function.
(dwarf_expr_context::execute_stack_op): Change to use
property_addr_info structure.
* dwarf2/expr.h (struct dwarf_expr_context): New evaluate
declaration. Change eval and fetch_result method to private.
(dwarf_expr_context::gdbarch): Remove member.
(dwarf_expr_context::stack): Make private and add m_ prefix.
(dwarf_expr_context::addr_size): Make private and add
m_ prefix.
(dwarf_expr_context::recursion_depth): Make private and add
m_ prefix.
(dwarf_expr_context::max_recursion_depth): Make private and
add m_ prefix.
(dwarf_expr_context::len): Make private and add m_ prefix.
(dwarf_expr_context::data): Make private and add m_ prefix.
(dwarf_expr_context::initialized): Make private and add
m_ prefix.
(dwarf_expr_context::pieces): Make private and add m_ prefix.
(dwarf_expr_context::per_objfile): Make private and add
m_ prefix.
(dwarf_expr_context::frame): Make private and add m_ prefix.
(dwarf_expr_context::per_cu): Make private and add m_ prefix.
(dwarf_expr_context::addr_info): Make private and add
m_ prefix.
* dwarf2/frame.c (execute_stack_op): Change to call evaluate
method.
* dwarf2/loc.c (dwarf2_evaluate_loc_desc_full): Change to call
evaluate method.
(dwarf2_locexpr_baton_eval): Change to call evaluate method.
The patch is addressing the issue of class users writing and reading
the internal data of the dwarf_expr_context class.
At this point, all conditions are met for the DWARF evaluator to return
an evaluation result in a form of a single struct value object.
gdb/ChangeLog:
* dwarf2/expr.c (pieced_value_funcs): Chenge to static
function.
(allocate_piece_closure): Change to static function.
(dwarf_expr_context::fetch_result): New function.
* dwarf2/expr.h (struct piece_closure): Remove declaration.
(struct dwarf_expr_context): fetch_result new declaration.
fetch, fetch_address and fetch_in_stack_memory members move
to private.
(allocate_piece_closure): Remove.
* dwarf2/frame.c (execute_stack_op): Change to use
fetch_result.
* dwarf2/loc.c (dwarf2_evaluate_loc_desc_full): Change to use
fetch_result.
(dwarf2_locexpr_baton_eval): Change to use fetch_result.
* dwarf2/loc.h (invalid_synthetic_pointer): Expose function.
Following 5 patches series is trying to clean up the interface of the
DWARF expression evaluator class (dwarf_expr_context).
After merging all expression evaluators into one class, the next
logical step is to make a clean user interface for that class. To do
that, we first need to address the issue of class users writing and
reading the internal data of the class directly.
Fixing the case of writing is simple, it makes sense for an evaluator
instance to be per architecture basis. Currently, the best separation
seems to be per object file, so having that data (dwarf2_per_objfile)
as a constructor argument makes sense. It also makes sense to get the
address size from that object file, but unfortunately that interface
does not exist at the moment.
Luckily, address size information is already available to the users
through other means. As a result, the address size also needs to be a
class constructor argument, at least until a better interface for
acquiring that information from an object file is implemented.
The rest of the user written data comes down to a context of an
evaluated expression (compilation unit context, frame context and
passed in buffer context) and a source type information that a result
of evaluating expression is representing. So, it makes sense for all of
these to be arguments of an evaluation method.
To address the problem of reading the dwarf_expr_context class
internal data, we first need to understand why it is implemented that
way?
This is actualy a question of which existing class can be used to
represent both values and a location descriptions and why it is not
used currently?
The answer is in a struct value class/structure, but the problem is
that before the evaluators were merged, only one evaluator had an
infrastructure to resolve composite and implicit pointer location
descriptions.
After the merge, we are now able to use the struct value to represent
any result of the expression evaluation. It also makes sense to move
all infrastructure for those location descriptions to the expr.c file
considering that that is the only place using that infrastructure.
What we are left with in the end is a clean public interface of the
dwarf_expr_context class containing:
- constructor,
- destructor,
- push_address method and
- eval_exp method.
The idea with this particular patch is to move piece_closure structure
and the interface that handles it (lval_funcs) to expr.c file.
While implicit pointer location descriptions are still not useful in
the CFI context (of the AMD's DWARF standard extensions), the composite
location descriptions are certainly necessary to describe a results of
specific compiler optimizations.
Considering that a piece_closure structure is used to represent both,
there was no benefit in splitting them.
gdb/ChangeLog:
* dwarf2/expr.c (struct piece_closure): Add from loc.c.
(allocate_piece_closure): Add from loc.c.
(bits_to_bytes): Add from loc.c.
(rw_pieced_value): Add from loc.c.
(read_pieced_value): Add from loc.c.
(write_pieced_value): Add from loc.c.
(check_pieced_synthetic_pointer): Add from loc.c.
(indirect_pieced_value): Add from loc.c.
(coerce_pieced_ref): Add from loc.c.
(copy_pieced_value_closure): Add from loc.c.
(free_pieced_value_closure): Add from loc.c.
(sect_variable_value): Add from loc.c.
* dwarf2/loc.c (sect_variable_value): Move to expr.c.
(struct piece_closure): Move to expr.c.
(allocate_piece_closure): Move to expr.c.
(bits_to_bytes): Move to expr.c.
(rw_pieced_value): Move to expr.c.
(read_pieced_value): Move to expr.c.
(write_pieced_value): Move to expr.c.
(check_pieced_synthetic_pointer): Move to expr.c.
(indirect_pieced_value): Move to expr.c.
(coerce_pieced_ref): Move to expr.c.
(copy_pieced_value_closure): Move to expr.c.
(free_pieced_value_closure): Move to expr.c.
The evaluate_for_locexpr_baton is the last derived class from the
dwarf_expr_context class. It's purpose is to support the passed in
buffer functionality.
Although, it is not really necessary to merge this class with it's
base class, doing that simplifies new expression evaluator design.
Considering that this functionality is going around the DWARF standard,
it is also reasonable to expect that with a new evaluator design and
extending the push object address functionality to accept any location
description, there will be no need to support passed in buffers.
Alternatively, it would also makes sense to abstract the interaction
between the evaluator and a given resource in the near future. The
passed in buffer would then be a specialization of that abstraction.
gdb/ChangeLog:
* dwarf2/expr.c (dwarf_expr_context::read_mem): Merge with
evaluate_for_locexpr_baton implementation.
* dwarf2/loc.c (class evaluate_for_locexpr_baton): Remove
class.
(evaluate_for_locexpr_baton::read_mem): Move to
dwarf_expr_context.
(dwarf2_locexpr_baton_eval): Instantiate dwarf_expr_context
instead of evaluate_for_locexpr_baton class.
There are no virtual methods that require different specialization in
dwarf_expr_context class. This means that derived classes
dwarf_expr_executor and dwarf_evaluate_loc_desc are not needed any
more.
As a result of this, the evaluate_for_locexpr_baton class base class
is now the dwarf_expr_context class.
There might be a need for a better class hierarchy when we know more
about the direction of the future DWARF versions and gdb extensions,
but that is out of the scope of this patch series.
gdb/ChangeLog:
* dwarf2/frame.c (class dwarf_expr_executor): Remove class.
(execute_stack_op): Instantiate dwarf_expr_context instead of
dwarf_evaluate_loc_desc class.
* dwarf2/loc.c (class dwarf_evaluate_loc_desc): Remove class.
(dwarf2_evaluate_loc_desc_full): Instantiate dwarf_expr_context
instead of dwarf_evaluate_loc_desc class.
(struct evaluate_for_locexpr_baton): Derive from
dwarf_expr_context.
Following the idea of merging the evaluators, the
push_dwarf_reg_entry_value method can be moved from
dwarf_expr_executor and dwarf_evaluate_loc_desc classes
to their base class dwarf_expr_context.
gdb/ChangeLog:
* dwarf2/expr.c
(dwarf_expr_context::push_dwarf_reg_entry_value): Move from
dwarf_evaluate_loc_desc.
* dwarf2/frame.c
(dwarf_expr_executor::push_dwarf_reg_entry_value): Remove
method.
* dwarf2/loc.c (dwarf_expr_reg_to_entry_parameter): Expose
function.
(dwarf_evaluate_loc_desc::push_dwarf_reg_entry_value): Move to
dwarf_expr_context.
* dwarf2/loc.h (dwarf_expr_reg_to_entry_parameter): Expose
function.
Following the idea of merging the evaluators, the read_mem method can
be moved from dwarf_expr_executor and dwarf_evaluate_loc_desc classes
to their base class dwarf_expr_context.
gdb/ChangeLog:
* dwarf2/expr.c (dwarf_expr_context::read_mem): Move from
dwarf_evaluate_loc_desc.
* dwarf2/frame.c (dwarf_expr_executor::read_mem): Remove
method.
* dwarf2/loc.c (dwarf_evaluate_loc_desc::read_mem): Move to
dwarf_expr_context.
Following the idea of merging the evaluators, the get_object_address
and can be moved from dwarf_expr_executor and dwarf_evaluate_loc_desc
classes to their base class dwarf_expr_context.
gdb/ChangeLog:
* dwarf2/expr.c (dwarf_expr_context::get_object_address): Move
from dwarf_evaluate_loc_desc.
(class dwarf_expr_context): Add object address member to
dwarf_expr_context.
* dwarf2/expr.h (dwarf_expr_context::get_frame_pc): Remove
method.
* dwarf2/frame.c (dwarf_expr_executor::get_object_address):
Remove method.
* dwarf2/loc.c (dwarf_evaluate_loc_desc::get_object_address):
move to dwarf_expr_context.
(class dwarf_evaluate_loc_desc): Move object address member to
dwarf_expr_context.
Following the idea of merging the evaluators, the dwarf_call and
get_frame_pc method can be moved from dwarf_expr_executor and
dwarf_evaluate_loc_desc classes to their base class dwarf_expr_context.
Once this is done, the get_frame_pc can be replace with lambda
function.
gdb/ChangeLog:
* dwarf2/expr.c (dwarf_expr_context::dwarf_call): Move from
dwarf_evaluate_loc_desc.
(dwarf_expr_context::get_frame_pc): Replace with lambda.
* dwarf2/expr.h (dwarf_expr_context::get_frame_pc): Remove
method.
* dwarf2/frame.c (dwarf_expr_executor::dwarf_call): Remove
method.
(dwarf_expr_executor::get_frame_pc): Remove method.
* dwarf2/loc.c (dwarf_evaluate_loc_desc::get_frame_pc): Remove
method.
(dwarf_evaluate_loc_desc::dwarf_call): Move to
dwarf_expr_context.
(per_cu_dwarf_call): Inline function.
This patch moves the compilation unit context information and support
from dwarf_expr_executor and dwarf_evaluate_loc_desc to
dwarf_expr_context evaluator. The idea is to report an error when a
given operation requires a compilation unit information to be resolved,
which is not available.
With this change, it also makes sense to always acquire ref_addr_size
information from the compilation unit context, considering that all
DWARF operations that refer to that information require a compilation
unit context to be present during their evaluation.
gdb/ChangeLog:
* dwarf2/expr.c (ensure_have_per_cu): New function.
(dwarf_expr_context::dwarf_expr_context): Add compilation unit
context information.
(dwarf_expr_context::get_base_type): Move from
dwarf_evaluate_loc_desc.
(dwarf_expr_context::get_addr_index): Remove method.
(dwarf_expr_context::dwarf_variable_value): Remove method.
(dwarf_expr_context::execute_stack_op): Call compilation unit
context info check. Inline get_addr_index and
dwarf_variable_value methods.
* dwarf2/expr.h (struct dwarf_expr_context): Add compilation
context info.
(dwarf_expr_context::get_addr_index): Remove method.
(dwarf_expr_context::dwarf_variable_value): Remove method.
(dwarf_expr_context::ref_addr_size): Remove member.
* dwarf2/frame.c (dwarf_expr_executor::get_addr_index): Remove
method.
(dwarf_expr_executor::dwarf_variable_value): Remove method.
* dwarf2/loc.c (sect_variable_value): Expose function.
(dwarf_evaluate_loc_desc::get_addr_index): Remove method.
(dwarf_evaluate_loc_desc::dwarf_variable_value): Remove method.
(class dwarf_evaluate_loc_desc): Move compilation unit context
information to dwarf_expr_context class.
* dwarf2/loc.h (sect_variable_value): Expose function.
Following the idea of merging the evaluators, the get_frame_cfa method
can be moved from dwarf_expr_executor and dwarf_evaluate_loc_desc
classes to their base class dwarf_expr_context. Once this is done,
it becomes apparent that the method is only called once and it can be
inlined.
It is also necessary to check if the frame context information was
provided before the DW_OP_call_frame_cfa operation is executed.
gdb/ChangeLog:
* dwarf2/expr.c (dwarf_expr_context::get_frame_cfa): Remove
method.
(dwarf_expr_context::execute_stack_op): Call frame context info
check for DW_OP_call_frame_cfa. Remove use of get_frame_cfa.
* dwarf2/expr.h (dwarf_expr_context::get_frame_cfa): Remove
method.
* dwarf2/frame.c (dwarf_expr_context::get_frame_cfa): Remove
method.
* dwarf2/loc.c (dwarf_expr_context::get_frame_cfa): Remove
method.
Following 15 patches in this patch series is cleaning up the design of
the DWARF expression evaluator (dwarf_expr_context) to make future
extensions of that evaluator easier and cleaner to implement.
There are three subclasses of the dwarf_expr_context class
(dwarf_expr_executor, dwarf_evaluate_loc_desc and
evaluate_for_locexpr_baton). Here is a short description of each class:
- dwarf_expr_executor is evaluating a DWARF expression in a context
of a Call Frame Information. The overridden methods of this subclass
report an error if a specific DWARF operation, represented by that
method, is not allowed in a CFI context. The source code of this
subclass lacks the support for composite as well as implicit pointer
location description.
- dwarf_evaluate_loc_desc can evaluate any expression with no
restrictions. All of the methods that this subclass overrides are
actually doing what they are intended to do. This subclass contains
a full support for all location description types.
- evaluate_for_locexpr_baton subclass is a specialization of the
dwarf_evaluate_loc_desc subclass and it's function is to add
support for passed in buffers. This seems to be a way to go around
the fact that DWARF standard lacks a bit offset support for memory
location descriptions as well as using any location description for
the push object address functionality.
It all comes down to this question: what is a function of a DWARF
expression evaluator?
Is it to evaluate the expression in a given context or to check the
correctness of that expression in that context?
Currently, the only reason why there is a dwarf_expr_executor subclass
is to report an invalid DWARF expression in a context of a CFI, but is
that what the evaluator is supposed to do considering that the evaluator
is not tied to a given DWARF version?
There are more and more vendor and GNU extensions that are not part of
the DWARF standard, so is it that impossible to expect that some of the
extensions could actually lift the previously imposed restrictions of
the CFI context? Not to mention that every new DWARF version is lifting
some restrictions anyway.
The thing that makes more sense for an evaluator to do, is to take the
context of an evaluation and checks the requirements of every operation
evaluated against that context. With this approach, the evaluator would
report an error only if parts of the context, necessary for the
evaluation, are missing.
If this approach is taken, then the unification of the
dwarf_evaluate_loc_desc, dwarf_expr_executor and dwarf_expr_context
is the next logical step. This makes a design of the DWARF expression
evaluator cleaner and allows more flexibility when supporting future
vendor and GNU extensions.
Additional benefit here is that now all evaluators have access to all
location description types, which means that a vendor extended CFI
rules could support composite location description as well. This also
means that a new evaluator interface can be changed to return a single
struct value (that describes the result of the evaluation) instead of
a caller poking around the dwarf_expr_context internal data for answers
(like it is done currently).
This patch starts the merging process by moving the frame context
information and support from dwarf_expr_executor and
dwarf_evaluate_loc_desc to dwarf_expr_context evaluator. The idea
is to report an error when a given operation requires a frame
information to be resolved, if that information is not present.
gdb/ChangeLog:
* dwarf2/expr.c (ensure_have_frame): New function.
(read_addr_from_reg): Add from frame.c.
(dwarf_expr_context::dwarf_expr_context): Add frame info to
dwarf_expr_context.
(dwarf_expr_context::read_addr_from_reg): Remove.
(dwarf_expr_context::get_reg_value): Move from
dwarf_evaluate_loc_desc.
(dwarf_expr_context::get_frame_base): Move from
dwarf_evaluate_loc_desc.
(dwarf_expr_context::execute_stack_op): Call frame context info
check. Remove use of read_addr_from_reg method.
* dwarf2/expr.h (struct dwarf_expr_context): Add frame info
member, read_addr_from_reg, get_reg_value and get_frame_base
declaration.
(read_addr_from_reg): Move to expr.c.
* dwarf2/frame.c (read_addr_from_reg): Move to
dwarf_expr_context.
(dwarf_expr_executor::read_addr_from_reg): Remove.
(dwarf_expr_executor::get_frame_base): Remove.
(dwarf_expr_executor::get_reg_value): Remove.
(execute_stack_op): Use read_addr_from_reg function instead of
read_addr_from_reg method.
* dwarf2/loc.c (dwarf_evaluate_loc_desc::get_frame_base): Move
to dwarf_expr_context.
(dwarf_evaluate_loc_desc::get_reg_value): Move to
dwarf_expr_context.
(dwarf_evaluate_loc_desc::read_addr_from_reg): Remove.
(dwarf2_locexpr_baton_eval):Use read_addr_from_reg function
instead of read_addr_from_reg method.
This patch addresses a design problem with the symbol_needs_eval_context
class. It exposes the problem by introducing two new testsuite test
cases.
To explain the issue, I first need to explain the dwarf_expr_context
class that the symbol_needs_eval_context class derives from.
The intention behind the dwarf_expr_context class is to commonize the
DWARF expression evaluation mechanism for different evaluation
contexts. Currently in gdb, the evaluation context can contain some or
all of the following information: architecture, object file, frame and
compilation unit.
Depending on the information needed to evaluate a given expression,
there are currently three distinct DWARF expression evaluators:
- Frame: designed to evaluate an expression in the context of a call
frame information (dwarf_expr_executor class). This evaluator doesn't
need a compilation unit information.
- Location description: designed to evaluate an expression in the
context of a source level information (dwarf_evaluate_loc_desc
class). This evaluator expects all information needed for the
evaluation of the given expression to be present.
- Symbol needs: designed to answer a question about the parts of the
context information required to evaluate a DWARF expression behind a
given symbol (symbol_needs_eval_context class). This evaluator
doesn't need a frame information.
The functional difference between the symbol needs evaluator and the
others is that this evaluator is not meant to interact with the actual
target. Instead, it is supposed to check which parts of the context
information are needed for the given DWARF expression to be evaluated by
the location description evaluator.
The idea is to take advantage of the existing dwarf_expr_context
evaluation mechanism and to fake all required interactions with the
actual target, by returning back dummy values. The evaluation result is
returned as one of three possible values, based on operations found in a
given expression:
- SYMBOL_NEEDS_NONE,
- SYMBOL_NEEDS_REGISTERS and
- SYMBOL_NEEDS_FRAME.
The problem here is that faking results of target interactions can yield
an incorrect evaluation result.
For example, if we have a conditional DWARF expression, where the
condition depends on a value read from an actual target, and the true
branch of the condition requires a frame information to be evaluated,
while the false branch doesn't, fake target reads could conclude that a
frame information is not needed, where in fact it is. This wrong
information would then cause the expression to be actually evaluated (by
the location description evaluator) with a missing frame information.
This would then crash the debugger.
The gdb.dwarf2/symbol_needs_eval_fail.exp test introduces this
scenario, with the following DWARF expression:
DW_OP_addr $some_variable
DW_OP_deref
# conditional jump to DW_OP_bregx
DW_OP_bra 4
DW_OP_lit0
# jump to DW_OP_stack_value
DW_OP_skip 3
DW_OP_bregx $dwarf_regnum 0
DW_OP_stack_value
This expression describes a case where some variable dictates the
location of another variable. Depending on a value of some_variable, the
variable whose location is described by this expression is either read
from a register or it is defined as a constant value 0. In both cases,
the value will be returned as an implicit location description on the
DWARF stack.
Currently, when the symbol needs evaluator fakes a memory read from the
address behind the some_variable variable, the constant value 0 is used
as the value of the variable A, and the check returns the
SYMBOL_NEEDS_NONE result.
This is clearly a wrong result and it causes the debugger to crash.
The scenario might sound strange to some people, but it comes from a
SIMD/SIMT architecture where $some_variable is an execution mask. In
any case, it is a valid DWARF expression, and GDB shouldn't crash while
evaluating it. Also, a similar example could be made based on a
condition of the frame base value, where if that value is concluded to
be 0, the variable location could be defaulted to a TLS based memory
address.
The gdb.dwarf2/symbol_needs_eval_timeout.exp test introduces a second
scenario. This scenario is a bit more abstract due to the DWARF
assembler lacking the CFI support, but it exposes a different
manifestation of the same problem. Like in the previous scenario, the
DWARF expression used in the test is valid:
DW_OP_lit1
DW_OP_addr $some_variable
DW_OP_deref
# jump to DW_OP_fbreg
DW_OP_skip 4
DW_OP_drop
DW_OP_fbreg 0
DW_OP_dup
DW_OP_lit0
DW_OP_eq
# conditional jump to DW_OP_drop
DW_OP_bra -9
DW_OP_stack_value
Similarly to the previous scenario, the location of a variable A is an
implicit location description with a constant value that depends on a
value held by a global variable. The difference from the previous case
is that DWARF expression contains a loop instead of just one branch. The
end condition of that loop depends on the expectation that a frame base
value is never zero. Currently, the act of faking the target reads will
cause the symbol needs evaluator to get stuck in an infinite loop.
Somebody could argue that we could change the fake reads to return
something else, but that would only hide the real problem.
The general impression seems to be that the desired design is to have
one class that deals with parsing of the DWARF expression, while there
are virtual methods that deal with specifics of some operations.
Using an evaluator mechanism here doesn't seem to be correct, because
the act of evaluation relies on accessing the data from the actual
target with the possibility of skipping the evaluation of some parts of
the expression.
To better explain the proposed solution for the issue, I first need to
explain a couple more details behind the current design:
There are multiple places in gdb that handle DWARF expression parsing
for different purposes. Some are in charge of converting the expression
to some other internal representation (decode_location_expression,
disassemble_dwarf_expression and dwarf2_compile_expr_to_ax), some are
analysing the expression for specific information
(compute_stack_depth_worker) and some are in charge of evaluating the
expression in a given context (dwarf_expr_context::execute_stack_op
and decode_locdesc).
The problem is that all those functions have a similar (large) switch
statement that handles each DWARF expression operation. The result of
this is a code duplication and harder maintenance.
As a step into the right direction to solve this problem (at least for
the purpose of a DWARF expression evaluation) the expression parsing was
commonized inside of an evaluator base class (dwarf_expr_context). This
makes sense for all derived classes, except for the symbol needs
evaluator (symbol_needs_eval_context) class.
As described previously the problem with this evaluator is that if the
evaluator is not allowed to access the actual target, it is not really
evaluating.
Instead, the desired function of a symbol needs evaluator seems to fall
more into expression analysis category. This means that a more natural
fit for this evaluator is to be a symbol needs analysis, similar to the
existing compute_stack_depth_worker analysis.
Another problem is that using a heavyweight mechanism of an evaluator
to do an expression analysis seems to be an unneeded overhead. It also
requires a more complicated design of the parent class to support fake
target reads.
The reality is that the whole symbol_needs_eval_context class can be
replaced with a lightweight recursive analysis function, that will give
more correct result without compromising the design of the
dwarf_expr_context class. The analysis treats the expression byte
stream as a DWARF operation graph, where each graph node can be
visited only once and each operation can decide if the frame context
is needed for their evaluation.
The downside of this approach is adding of one more similar switch
statement, but at least this way the new symbol needs analysis will be
a lightweight mechnism and it will provide a correct result for any
given DWARF expression.
A more desired long term design would be to have one class that deals
with parsing of the DWARF expression, while there would be a virtual
methods that deal with specifics of some DWARF operations. Then that
class would be used as a base for all DWARF expression parsing mentioned
at the beginning.
This however, requires a far bigger changes that are out of the scope
of this patch series.
The new analysis requires the DWARF location description for the
argc argument of the main function to change in the assembly file
gdb.python/amd64-py-framefilter-invalidarg.S. Originally, expression
ended with a 0 value byte, which was never reached by the symbol needs
evaluator, because it was detecting a stack underflow when evaluating
the operation before. The new approach does not simulate a DWARF
stack anymore, so the 0 value byte needs to be removed because it
makes the DWARF expression invalid.
gdb/ChangeLog:
* dwarf2/loc.c (class symbol_needs_eval_context): Remove.
(dwarf2_get_symbol_read_needs): New function.
(dwarf2_loc_desc_get_symbol_read_needs): Remove.
(locexpr_get_symbol_read_needs): Use
dwarf2_get_symbol_read_needs.
gdb/testsuite/ChangeLog:
* gdb.python/amd64-py-framefilter-invalidarg.S : Update argc
DWARF location expression.
* lib/dwarf.exp (_location): Handle DW_OP_fbreg.
* gdb.dwarf2/symbol_needs_eval.c: New file.
* gdb.dwarf2/symbol_needs_eval_fail.exp: New file.
* gdb.dwarf2/symbol_needs_eval_timeout.exp: New file.
Without that it is impossible to debug on riscv64.
gdb/
PR symtab/27999
* dwarf2/loc.c (decode_debug_loclists_addresses): Support
DW_LLE_start_end.
gdb/testsuite/
PR symtab/27999
* lib/dwarf.exp (start_end): New proc inside loclists.
* gdb.dwarf2/loclists-start-end.exp: New file.
* gdb.dwarf2/loclists-start-end.c: New file.
With -fgnat-encodings=minimal, an internal version (these patches will
be upstreamed in the near future) of the Ada compiler can emit DWARF
for an array where the bound comes from a variable, like:
<1><12a7>: Abbrev Number: 7 (DW_TAG_array_type)
<12a8> DW_AT_name : (indirect string, offset: 0x1ae9): pck__my_array
[...]
<2><12b4>: Abbrev Number: 8 (DW_TAG_subrange_type)
<12b5> DW_AT_type : <0x1294>
<12b9> DW_AT_upper_bound : <0x1277>
With the upper bound DIE being:
<1><1277>: Abbrev Number: 2 (DW_TAG_variable)
<1278> DW_AT_name : (indirect string, offset: 0x1a4d): pck__my_length___U
<127c> DW_AT_type : <0x128f>
<1280> DW_AT_external : 1
<1280> DW_AT_artificial : 1
<1280> DW_AT_declaration : 1
Note that the variable is just a declaration -- in this situation, the
variable comes from another compilation unit, and must be found when
trying to compute the array bound.
This patch adds a new PROP_VARIABLE_NAME kind, to enable this search.
This same scenario can occur with DW_OP_GNU_variable_value, so this
patch adds support for that as well.
gdb/ChangeLog
2021-06-04 Tom Tromey <tromey@adacore.com>
* dwarf2/read.h (dwarf2_fetch_die_type_sect_off): Add 'var_name'
parameter.
* dwarf2/loc.c (dwarf2_evaluate_property) <case
PROP_VARIABLE_NAME>: New case.
(compute_var_value): New function.
(sect_variable_value): Use compute_var_value.
* dwarf2/read.c (attr_to_dynamic_prop): Handle DW_TAG_variable.
(var_decl_name): New function.
(dwarf2_fetch_die_type_sect_off): Add 'var_name' parameter.
* gdbtypes.h (enum dynamic_prop_kind) <PROP_VARIABLE_NAME>: New
constant.
(union dynamic_prop_data) <variable_name>: New member.
(struct dynamic_prop) <variable_name, set_variable_name>: New
methods.
gdb/testsuite/ChangeLog
2021-06-04 Tom Tromey <tromey@adacore.com>
* gdb.ada/array_of_symbolic_length.exp: New file.
* gdb.ada/array_of_symbolic_length/foo.adb: New file.
* gdb.ada/array_of_symbolic_length/gl.adb: New file.
* gdb.ada/array_of_symbolic_length/gl.ads: New file.
* gdb.ada/array_of_symbolic_length/pck.adb: New file.
* gdb.ada/array_of_symbolic_length/pck.ads: New file.
With GCC trunk, gdb.ada/access_to_packed_array.exp causes a GDB crash.
The problem is that ptype tries to resolve a dynamic type. However,
the inferior is not running, so there are no frames.
This patch updates dwarf2_evaluate_loc_desc::get_frame_base to handle
this situation.
gdb/ChangeLog
2021-05-17 Tom Tromey <tromey@adacore.com>
* dwarf2/loc.c (dwarf2_evaluate_loc_desc::get_frame_base): Throw
if frame is null.
This changes the GDB compile code to use std::vector<bool> when
computing which registers are used. This is a bit more idiomatic, but
the main benefit is that it also adds some checking when the libstd++
debug mode is enabled.
2021-01-23 Tom Tromey <tom@tromey.com>
* symtab.h (struct symbol_computed_ops) <generate_c_location>:
Change type of "registers_used".
* dwarf2/loc.h (dwarf2_compile_property_to_c): Update.
* dwarf2/loc.c (dwarf2_compile_property_to_c)
(locexpr_generate_c_location, loclist_generate_c_location): Change
type of "registers_used".
* compile/compile.h (compile_dwarf_expr_to_c)
(compile_dwarf_bounds_to_c): Update.
* compile/compile-loc2c.c (pushf_register_address)
(pushf_register, do_compile_dwarf_expr_to_c)
(compile_dwarf_expr_to_c, compile_dwarf_bounds_to_c): Change type
of "registers_used".
* compile/compile-c.h (generate_c_for_variable_locations):
Update.
* compile/compile-c-symbols.c (generate_vla_size)
(generate_c_for_for_one_variable): Change type of
"registers_used".
(generate_c_for_variable_locations): Return std::vector.
* compile/compile-c-support.c (generate_register_struct): Change
type of "registers_used".
(compute): Update.
This commits the result of running gdb/copyright.py as per our Start
of New Year procedure...
gdb/ChangeLog
Update copyright year range in copyright header of all GDB files.
