Messages in this thread Patch in this message | | | From | Sami Tolvanen <> | Date | Tue, 6 Sep 2022 17:47:23 -0700 | Subject | Re: [PATCH] objtool: Fix symbol creation |
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On Wed, May 18, 2022 at 3:10 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Wed, May 18, 2022 at 10:36:04AM -0700, Josh Poimboeuf wrote: > > On Wed, May 18, 2022 at 09:41:52AM +0200, Peter Zijlstra wrote: > > > +static int elf_update_symbol(struct elf *elf, struct section *symtab, > > > + struct section *symtab_shndx, struct symbol *sym) > > > { > > > - Elf_Data *data, *shndx_data = NULL; > > > - Elf32_Word first_non_local; > > > - struct symbol *sym; > > > - Elf_Scn *s; > > > - > > > - first_non_local = symtab->sh.sh_info; > > > - > > > - sym = find_symbol_by_index(elf, first_non_local); > > > - if (!sym) { > > > - WARN("no non-local symbols !?"); > > > - return first_non_local; > > > - } > > > + Elf_Data *symtab_data = NULL, *shndx_data = NULL; > > > + Elf64_Xword entsize = symtab->sh.sh_entsize; > > > + Elf32_Word shndx = sym->sec->idx; > > > > So if it's a global UNDEF symbol then I think 'sym->sec' can be NULL and > > this blows up? > > Oh indeed, sym->sec ? sym->sec->idx : SHN_UNDEF it is.
elf_update_symbol seems to be a bit broken even after this. I noticed it converts SHN_ABS symbols into SHN_UNDEF, which breaks some KCFI builds. In fact, the function drops all the special st_shndx values except SHN_XINDEX.
Specifically, read_symbols sets sym->sec to find_section_by_index(elf, 0) for all SHN_UNDEF and special st_shndx symbols, which means sym->sec is non-NULL and sym->sec->idx is always 0 (= SHN_UNDEF) for these symbols. As elf_update_symbol doesn't look at the actual st_shndx value, it ends up marking the symbols undefined.
This quick hack fixes the issue for me, but I'm not sure if it's the cleanest solution. Any thoughts?
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index c25e957c1e52..7e24b09b1163 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -619,6 +619,11 @@ static int elf_update_symbol(struct elf *elf, struct section *symtab, Elf64_Xword entsize = symtab->sh.sh_entsize; int max_idx, idx = sym->idx; Elf_Scn *s, *t = NULL; + bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE && + sym->sym.st_shndx != SHN_XINDEX; + + if (is_special_shndx) + shndx = sym->sym.st_shndx;
s = elf_getscn(elf->elf, symtab->idx); if (!s) { @@ -704,7 +709,7 @@ static int elf_update_symbol(struct elf *elf, struct section *symtab, }
/* setup extended section index magic and write the symbol */ - if (shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) { + if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) { sym->sym.st_shndx = shndx; if (!shndx_data) shndx = 0; Sami
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