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create-diff-object: strip unused CSWTCH symbols

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Fixes: #532
This commit is contained in:
Josh Poimboeuf 2015-10-28 18:44:38 -05:00
parent 98f892b273
commit fd0c1bbe9c
1 changed files with 37 additions and 0 deletions
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37
kpatch-build/create-diff-object.c
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@ -513,6 +513,41 @@ struct kpatch_elf *kpatch_elf_open(const char *name)
return kelf;
}
static void kpatch_strip_unused_switch_syms(struct kpatch_elf *kelf)
{
struct symbol *sym, *safe;
char *sec_suffix;
/*
* CSWTCH is a read-only static local array used by gcc for some switch
* statements. If two functions use the same CSWTCH data, there can be
* two separate symbols (CSWTCH.x and CSWTCH.y) referring to the same
* bundled .rodata.CSWTCH.x section. Having two mangled symbols
* associated with the same bundled section, when only one of them
* matches the name of the bundled section, creates a lot of confusion
* in the correlation logic. Eliminate that confusion by getting rid
* of the symbol which has a different number suffix than the bundled
* section.
*
* Due to the behavior of -fdata-sections, there shouldn't be any
* references to the symbol. Instead, all references are to its
* bundled section. So removing it should be safe.
*/
list_for_each_entry_safe(sym, safe, &kelf->symbols, list) {
if (sym->type != STT_OBJECT || sym->bind != STB_LOCAL ||
strncmp(sym->name, "CSWTCH.", 7))
continue;
sec_suffix = strstr(sym->sec->name, "CSWTCH.");
if (!sec_suffix)
ERROR("unexpected section name %s for CSWTCH symbol %s",
sym->sec->name, sym->name);
if (strcmp(sym->name, sec_suffix))
list_del(&sym->list);
}
}
/*
* This function detects whether the given symbol is a "special" static local
* variable (for lack of a better term).
@ -2967,6 +3002,8 @@ int main(int argc, char *argv[])
kpatch_check_program_headers(kelf_base->elf);
kpatch_check_program_headers(kelf_patched->elf);
kpatch_strip_unused_switch_syms(kelf_base);
kpatch_strip_unused_switch_syms(kelf_patched);
kpatch_mark_grouped_sections(kelf_patched);
kpatch_replace_sections_syms(kelf_base);
kpatch_replace_sections_syms(kelf_patched);