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| author | Peter Zijlstra <peterz@infradead.org> | 2022-03-08 16:30:46 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-03-15 10:32:43 +0100 |
| commit | 4adb23686795e9c88e3217b5d7b4524c0da9d04f (patch) | |
| tree | 3e82aa694a452dd067389d5f551d996cef0715b6 /tools/objtool/include | |
| parent | 53f7109ef957315ab53205ba3a3f4f48874c0428 (diff) | |
| download | linux-4adb23686795e9c88e3217b5d7b4524c0da9d04f.tar.bz2 | |
objtool: Ignore extra-symbol code
There's a fun implementation detail on linking STB_WEAK symbols. When
the linker combines two translation units, where one contains a weak
function and the other an override for it. It simply strips the
STB_WEAK symbol from the symbol table, but doesn't actually remove the
code.
The result is that when objtool is ran in a whole-archive kind of way,
it will encounter *heaps* of unused (and unreferenced) code. All
rudiments of weak functions.
Additionally, when a weak implementation is split into a .cold
subfunction that .cold symbol is left in place, even though completely
unused.
Teach objtool to ignore such rudiments by searching for symbol holes;
that is, code ranges that fall outside the given symbol bounds.
Specifically, ignore a sequence of unreachable instruction iff they
occupy a single hole, additionally ignore any .cold subfunctions
referenced.
Both ld.bfd and ld.lld behave like this. LTO builds otoh can (and do)
properly DCE weak functions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.232019347@infradead.org
Diffstat (limited to 'tools/objtool/include')
| -rw-r--r-- | tools/objtool/include/objtool/elf.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index d22336781401..22ba7e2b816e 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -152,6 +152,7 @@ struct symbol *find_func_by_offset(struct section *sec, unsigned long offset); struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset); struct symbol *find_symbol_by_name(const struct elf *elf, const char *name); struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset); +int find_symbol_hole_containing(const struct section *sec, unsigned long offset); struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset); struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec, unsigned long offset, unsigned int len); |