Searched hist:"4 adb2368" (Results 1 – 3 of 3) sorted by relevance
/openbmc/linux/tools/objtool/include/objtool/ |
H A D | elf.h | 4adb2368 Tue Mar 08 09:30:46 CST 2022 Peter Zijlstra <peterz@infradead.org> 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
|
/openbmc/linux/tools/objtool/ |
H A D | elf.c | 4adb2368 Tue Mar 08 09:30:46 CST 2022 Peter Zijlstra <peterz@infradead.org> 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
|
H A D | check.c | 4adb2368 Tue Mar 08 09:30:46 CST 2022 Peter Zijlstra <peterz@infradead.org> 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
|