Messages in this thread Patch in this message | | | Date | Wed, 16 Jun 2021 17:01:10 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3] recordmcount: Correct st_shndx handling |
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On Wed, Jun 16, 2021 at 12:23:13AM +0800, Mark-PK Tsai wrote: > From: Peter Zijlstra <peterz@infradead.org> > > One should only use st_shndx when >SHN_UNDEF and <SHN_LORESERVE. When > SHN_XINDEX, then use .symtab_shndx. Otherwise use 0. > > This handles the case: st_shndx >= SHN_LORESERVE && st_shndx != SHN_XINDEX. > > Reported-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Tested-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com> > [handle endianness of sym->st_shndx] > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com> > --- > scripts/recordmcount.h | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h > index f9b19524da11..ef9c3425f86b 100644 > --- a/scripts/recordmcount.h > +++ b/scripts/recordmcount.h > @@ -194,13 +194,18 @@ static unsigned int get_symindex(Elf_Sym const *sym, Elf32_Word const *symtab, > unsigned long offset; > int index; > > + if (w2(sym->st_shndx) > SHN_UNDEF && > + w2(sym->st_shndx) < SHN_LORESERVE) > return w2(sym->st_shndx); > > + if (w2(sym->st_shndx) == SHN_XINDEX) { > + offset = (unsigned long)sym - (unsigned long)symtab; > + index = offset / sizeof(*sym); > > + return w(symtab_shndx[index]); > + } > + > + return 0; > }
Thanks. However that leads to atrocious codegen because w2 is an indirect function, something like the below seems much better.
1d00: 41 0f b7 7f 0e movzwl 0xe(%r15),%edi 1d05: c0 eb 04 shr $0x4,%bl 1d08: ff 15 7a 54 00 00 callq *0x547a(%rip) # 7188 <w2> 1d0e: 85 c0 test %eax,%eax 1d10: 74 16 je 1d28 <main+0xba8> 1d12: 41 0f b7 7f 0e movzwl 0xe(%r15),%edi 1d17: ff 15 6b 54 00 00 callq *0x546b(%rip) # 7188 <w2> 1d1d: 3d ff fe 00 00 cmp $0xfeff,%eax 1d22: 0f 86 00 03 00 00 jbe 2028 <main+0xea8> 1d28: 41 0f b7 7f 0e movzwl 0xe(%r15),%edi 1d2d: ff 15 55 54 00 00 callq *0x5455(%rip) # 7188 <w2>
vs
1d0c: 41 0f b7 7f 0e movzwl 0xe(%r15),%edi 1d11: ff 15 71 54 00 00 callq *0x5471(%rip) # 7188 <w2>
--- diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h index f9b19524da11..b3e9d0563c03 100644 --- a/scripts/recordmcount.h +++ b/scripts/recordmcount.h @@ -192,15 +192,23 @@ static unsigned int get_symindex(Elf_Sym const *sym, Elf32_Word const *symtab, Elf32_Word const *symtab_shndx) { unsigned long offset; + unsigned short shndx; int index; - if (sym->st_shndx != SHN_XINDEX) - return w2(sym->st_shndx); + shndx = w2(sym->st_shndx); - offset = (unsigned long)sym - (unsigned long)symtab; - index = offset / sizeof(*sym); + if (shndx > SHN_UNDEF && + shndx < SHN_LORESERVE) + return shndx; - return w(symtab_shndx[index]); + if (shndx == SHN_XINDEX) { + offset = (unsigned long)sym - (unsigned long)symtab; + index = offset / sizeof(*sym); + + return w(symtab_shndx[index]); + } + + return 0; } static unsigned int get_shnum(Elf_Ehdr const *ehdr, Elf_Shdr const *shdr0)
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