A customer reported a failure to unwind in a certain core dump. A
lengthy investigation showed that the problem came from the
interaction between the tailcall and inline frame sniffers.
Normally, the regular DWARF unwinder may discover a chain of tail
calls ending in the current frame. In this case, it sets a member on
the dwarf2_frame_cache object, so that a subsequent call into the
tailcall sniffer will create the tailcall frames.
However, in this scenario, what happened is that the DWARF unwinder
did find tailcall frames -- but then the PC of the first such frame
was recognized and claimed by the inline frame sniffer.
This then caused unwinding to go astray further up the stack.
This patch fixes the problem by arranging for the tailcall sniffer to
be called before the inline sniffer. This way, if a DWARF frame has
tailcall information, the tailcalls will always be processed first.
This is safe to do, because the tailcall sniffer can only claim a
frame if the previous frame did in fact find this information. (So,
for example, if no DWARF frame is ever found, then this sniffer will
never trigger.)
This patch also partially reverts:
commit 1ec56e88aa
Author: Pedro Alves <palves@redhat.com>
Date: Fri Nov 22 13:17:46 2013 +0000
Eliminate dwarf2_frame_cache recursion, don't unwind from the dwarf2 sniffer (move dwarf2_tailcall_sniffer_first elsewhere).
That patch moved the call to dwarf2_tailcall_sniffer_first out of
dwarf2_frame_cache, and into dwarf2_frame_prev_register. However, in
this situation, this is too late -- by the time
dwarf2_frame_prev_register is called, the frame in question is already
recognized by the inline frame sniffer.
Rather than fully revert that patch, though, this just arranges to
call dwarf2_tailcall_sniffer_first from dwarf2_frame_cache -- which is
called shortly after the DWARF frame sniffer succeeds, via
compute_frame_id.
I don't know how to write a test case for this.
gdb/ChangeLog
2020-03-03 Tom Tromey <tromey@adacore.com>
* dwarf2/frame.c (struct dwarf2_frame_cache)
<checked_tailcall_bottom, entry_cfa_sp_offset,
entry_cfa_sp_offset_p>: Remove members.
(dwarf2_frame_cache): Call dwarf2_tailcall_sniffer_first.
(dwarf2_frame_prev_register): Don't call
dwarf2_tailcall_sniffer_first.
(dwarf2_append_unwinders): Don't append tailcall unwinder.
* frame-unwind.c (add_unwinder): New fuction.
(frame_unwind_init): Use it. Add tailcall unwinder.
Now that comp_unit and the remaining frame data are all independent of
the objfile, it can all be stored on the BFD and shared across
inferiors.
As with other code doing this same thing, care must be taken to not
share the data when the objfile requires relocations. So, two keys
are used: one for the BFD and one for the objfile, and
gdb_bfd_requires_relocations is used to differentiate between the two
cases.
gdb/ChangeLog
2020-02-12 Tom Tromey <tom@tromey.com>
* dwarf2/frame.c (dwarf2_frame_bfd_data): New global.
(dwarf2_frame_objfile_data): Add comment.
(find_comp_unit, set_comp_unit): New functions.
(dwarf2_frame_find_fde): Use find_comp_unit.
(dwarf2_build_frame_info): Use set_comp_unit.
This removes the objfile backlink from comp_unit. The only remaining
uses involved fetching the text offset from the objfile. However,
this is already conveniently computed at all the sites that call
execute_cfa_program, and so it can simply be passed in.
gdb/ChangeLog
2020-02-12 Tom Tromey <tom@tromey.com>
* dwarf2/frame.c (struct comp_unit) <objfile>: Remove.
(comp_unit): Don't initialize objfile.
(execute_cfa_program): Add text_offset parameter.
(execute_cfa_program_test, dwarf2_fetch_cfa_info)
(dwarf2_frame_cache): Update.
(dwarf2_build_frame_info): Don't set "objfile" member.
The DWARF frame comp_unit object still has a backlink to the objfile.
In order to be truly objfile-independent, this must be removed.
This patch removes one such use, by passing the gdbarch to
decode_frame_entry directly.
gdb/ChangeLog
2020-02-12 Tom Tromey <tom@tromey.com>
* dwarf2/frame.c (decode_frame_entry_1): Add gdbarch parameter.
(decode_frame_entry): Likewise.
(dwarf2_build_frame_info): Update.
This adds an auto_obstack to the DWARF frame comp_unit object, and
then changes the remaining code here to use the comp_unit obstack
rather than the objfile obstack.
At this point, all the storage for frame data is self-contained --
that is, it is independent of the objfile.
gdb/ChangeLog
2020-02-12 Tom Tromey <tom@tromey.com>
* dwarf2/frame.c (struct comp_unit) <obstack>: New member.
(decode_frame_entry_1): Use the comp_unit obstack.
This changes the DWARF frame code to store the comp_unit on the
objfile, rather than storing the FDE table. It also changes the
comp_unit to be heap-allocated using "new".
This change makes it simpler for a later patch to add a field to the
comp_unit, and to have deallaction work properly. This in turn is
important for making the frame data be independent of the objfile.
gdb/ChangeLog
2020-02-12 Tom Tromey <tom@tromey.com>
* dwarf2/frame.c (struct comp_unit): Add initializers and
constructor.
(dwarf2_frame_objfile_data): Store a comp_unit.
(dwarf2_frame_find_fde): Update.
(dwarf2_build_frame_info): Use "new".
This removes struct dwarf2_fde_table, replacing it with a typedef of
std::vector. This simplifies the code somewhat.
gdb/ChangeLog
2020-02-12 Tom Tromey <tom@tromey.com>
* dwarf2/frame.c (struct dwarf2_fde_table): Remove.
(dwarf2_fde_table): Typedef for std::vector.
(dwarf2_frame_objfile_data): Remove the deleter. Now static.
(dwarf2_frame_find_fde, add_fde, decode_frame_entry_1)
(decode_frame_entry): Update.
(dwarf2_build_frame_info): Use "new".
There are two implementations of read_initial_length in gdb. This
merges them and moves the resulting function to leb.c.
2020-02-08 Tom Tromey <tom@tromey.com>
* dwarf2/read.c (read_initial_length): Move to leb.c.
* dwarf2/leb.h (read_initial_length): Declare.
* dwarf2/leb.c (read_initial_length): Move from read.c. Add
handle_nonstd parameter.
* dwarf2/frame.c (read_initial_length): Remove.
(decode_frame_entry_1): Update.
Change-Id: I34d37bad0f8a584bfa781432cba25e05e1bd5750
