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Handle copy relocations

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In ELF, if a data symbol is defined in a shared library and used by
the main program, it will be subject to a "copy relocation".  In this
scenario, the main program has a copy of the symbol in question, and a
relocation that tells ld.so to copy the data from the shared library.
Then the symbol in the main program is used to satisfy all references.

This patch changes gdb to handle this scenario.  Data symbols coming
from ELF shared libraries get a special flag that indicates that the
symbol's address may be subject to copy relocation.

I looked briefly into handling copy relocations by looking at the
actual relocations in the main program, but this seemed difficult to
do with BFD.

Note that no caching is done here.  Perhaps this could be changed if
need be; I wanted to avoid possible problems with either objfile
lifetimes and changes, or conflicts with the long-term (vapor-ware)
objfile splitting project.

gdb/ChangeLog
2019-10-02  Tom Tromey  <tromey@adacore.com>

	* symmisc.c (dump_msymbols): Don't use MSYMBOL_VALUE_ADDRESS.
	* ada-lang.c (lesseq_defined_than): Handle
	LOC_STATIC.
	* dwarf2read.c (dwarf2_per_objfile): Add can_copy
	parameter.
	(dwarf2_has_info): Likewise.
	(new_symbol): Set maybe_copied on symbol when
	appropriate.
	* dwarf2read.h (dwarf2_per_objfile): Add can_copy
	parameter.
	<can_copy>: New member.
	* elfread.c (record_minimal_symbol): Set maybe_copied
	on symbol when appropriate.
	(elf_symfile_read): Update call to dwarf2_has_info.
	* minsyms.c (lookup_minimal_symbol_linkage): New
	function.
	* minsyms.h (lookup_minimal_symbol_linkage): Declare.
	* symtab.c (get_symbol_address, get_msymbol_address):
	New functions.
	* symtab.h (get_symbol_address, get_msymbol_address):
	Declare.
	(SYMBOL_VALUE_ADDRESS, MSYMBOL_VALUE_ADDRESS): Handle
	maybe_copied.
	(struct symbol, struct minimal_symbol) <maybe_copied>:
	New member.
This commit is contained in:
Tom Tromey 2019-06-25 12:50:45 -06:00
parent 1dd5885077
commit 4b610737f0
11 changed files with 208 additions and 32 deletions
Download patch file Download diff file Expand all files Collapse all files

42
gdb/symtab.h
View file

@ -454,6 +454,14 @@ extern const char *symbol_get_demangled_name
extern CORE_ADDR symbol_overlayed_address (CORE_ADDR, struct obj_section *);
/* Return the address of SYM. The MAYBE_COPIED flag must be set on
SYM. If SYM appears in the main program's minimal symbols, then
that minsym's address is returned; otherwise, SYM's address is
returned. This should generally only be used via the
SYMBOL_VALUE_ADDRESS macro. */
extern CORE_ADDR get_symbol_address (const struct symbol *sym);
/* Note that all the following SYMBOL_* macros are used with the
SYMBOL argument being either a partial symbol or
a full symbol. Both types have a ginfo field. In particular
@ -463,7 +471,9 @@ extern CORE_ADDR symbol_overlayed_address (CORE_ADDR, struct obj_section *);
field only, instead of the SYMBOL parameter. */
#define SYMBOL_VALUE(symbol) (symbol)->ginfo.value.ivalue
#define SYMBOL_VALUE_ADDRESS(symbol) ((symbol)->ginfo.value.address + 0)
#define SYMBOL_VALUE_ADDRESS(symbol) \
(((symbol)->maybe_copied) ? get_symbol_address (symbol) \
: ((symbol)->ginfo.value.address))
#define SET_SYMBOL_VALUE_ADDRESS(symbol, new_value) \
((symbol)->ginfo.value.address = (new_value))
#define SYMBOL_VALUE_BYTES(symbol) (symbol)->ginfo.value.bytes
@ -671,6 +681,14 @@ struct minimal_symbol : public general_symbol_info
the object file format may not carry that piece of information. */
unsigned int has_size : 1;
/* For data symbols only, if this is set, then the symbol might be
subject to copy relocation. In this case, a minimal symbol
matching the symbol's linkage name is first looked for in the
main objfile. If found, then that address is used; otherwise the
address in this symbol is used. */
unsigned maybe_copied : 1;
/* Minimal symbols with the same hash key are kept on a linked
list. This is the link. */
@ -690,6 +708,15 @@ struct minimal_symbol : public general_symbol_info
bool text_p () const;
};
/* Return the address of MINSYM, which comes from OBJF. The
MAYBE_COPIED flag must be set on MINSYM. If MINSYM appears in the
main program's minimal symbols, then that minsym's address is
returned; otherwise, MINSYM's address is returned. This should
generally only be used via the MSYMBOL_VALUE_ADDRESS macro. */
extern CORE_ADDR get_msymbol_address (struct objfile *objf,
const struct minimal_symbol *minsym);
#define MSYMBOL_TARGET_FLAG_1(msymbol) (msymbol)->target_flag_1
#define MSYMBOL_TARGET_FLAG_2(msymbol) (msymbol)->target_flag_2
#define MSYMBOL_SIZE(msymbol) ((msymbol)->size + 0)
@ -708,8 +735,9 @@ struct minimal_symbol : public general_symbol_info
/* The relocated address of the minimal symbol, using the section
offsets from OBJFILE. */
#define MSYMBOL_VALUE_ADDRESS(objfile, symbol) \
((symbol)->value.address \
+ ANOFFSET ((objfile)->section_offsets, ((symbol)->section)))
(((symbol)->maybe_copied) ? get_msymbol_address (objfile, symbol) \
: ((symbol)->value.address \
+ ANOFFSET ((objfile)->section_offsets, ((symbol)->section))))
/* For a bound minsym, we can easily compute the address directly. */
#define BMSYMBOL_VALUE_ADDRESS(symbol) \
MSYMBOL_VALUE_ADDRESS ((symbol).objfile, (symbol).minsym)
@ -1112,6 +1140,14 @@ struct symbol
/* Whether this is an inlined function (class LOC_BLOCK only). */
unsigned is_inlined : 1;
/* For LOC_STATIC only, if this is set, then the symbol might be
subject to copy relocation. In this case, a minimal symbol
matching the symbol's linkage name is first looked for in the
main objfile. If found, then that address is used; otherwise the
address in this symbol is used. */
unsigned maybe_copied : 1;
/* The concrete type of this symbol. */
ENUM_BITFIELD (symbol_subclass_kind) subclass : 2;