Messages in this thread | | | From | Fāng-ruì Sòng <> | Date | Fri, 22 Jan 2021 00:49:43 -0800 | Subject | Re: [PATCH v3] x86: Treat R_386_PLT32 as R_386_PC32 |
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On Thu, Jan 14, 2021 at 2:48 PM Fangrui Song <maskray@google.com> wrote: > > This is similar to commit b21ebf2fb4cd ("x86: Treat R_X86_64_PLT32 as > R_X86_64_PC32"), but for i386. As far as Linux kernel is concerned, > R_386_PLT32 can be treated the same as R_386_PC32. > > R_386_PC32/R_X86_64_PC32 are PC-relative relocation types with the > requirement that the symbol address is significant. > R_386_PLT32/R_X86_64_PLT32 are PC-relative relocation types without the > address significance requirement. > > On x86-64, there is no PIC vs non-PIC PLT distinction and an > R_X86_64_PLT32 relocation is produced for both `call/jmp foo` and > `call/jmp foo@PLT` with newer (2018) GNU as/LLVM integrated assembler. > > On i386, there are 2 types of PLTs, PIC and non-PIC. Currently the > convention is to use R_386_PC32 for non-PIC PLT and R_386_PLT32 for PIC > PLT. > > clang-12 -fno-pic (since > https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6) > can emit R_386_PLT32 for compiler generated function declarations as > well to avoid a canonical PLT entry (st_shndx=0, st_value!=0) if the > symbol turns out to be defined externally. GCC/GNU as will likely keep > using R_386_PC32 because (1) the ABI is legacy (2) the change will drop > a GNU ld non-default visibility ifunc for shared objects. > https://sourceware.org/bugzilla/show_bug.cgi?id=27169 > > Link: https://github.com/ClangBuiltLinux/linux/issues/1210 > Reported-by: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Fangrui Song <maskray@google.com> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> > Tested-by: Nick Desaulniers <ndesaulniers@google.com> > Tested-by: Nathan Chancellor <natechancellor@gmail.com> > > --- > Change in v2: > * Improve commit message > --- > Change in v3: > * Change the GCC link to the more relevant GNU as link. > * Fix the relevant llvm-project commit id. > --- > arch/x86/kernel/module.c | 1 + > arch/x86/tools/relocs.c | 2 ++ > 2 files changed, 3 insertions(+) > > diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c > index 34b153cbd4ac..5e9a34b5bd74 100644 > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -114,6 +114,7 @@ int apply_relocate(Elf32_Shdr *sechdrs, > *location += sym->st_value; > break; > case R_386_PC32: > + case R_386_PLT32: > /* Add the value, subtract its position */ > *location += sym->st_value - (uint32_t)location; > break; > diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c > index ce7188cbdae5..717e48ca28b6 100644 > --- a/arch/x86/tools/relocs.c > +++ b/arch/x86/tools/relocs.c > @@ -867,6 +867,7 @@ static int do_reloc32(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, > case R_386_PC32: > case R_386_PC16: > case R_386_PC8: > + case R_386_PLT32: > /* > * NONE can be ignored and PC relative relocations don't > * need to be adjusted. > @@ -910,6 +911,7 @@ static int do_reloc_real(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, > case R_386_PC32: > case R_386_PC16: > case R_386_PC8: > + case R_386_PLT32: > /* > * NONE can be ignored and PC relative relocations don't > * need to be adjusted. > -- > 2.30.0.296.g2bfb1c46d8-goog >
Ping:)
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