On Wed, Jan 06, 2021 at 04:17:39PM -0800, Fangrui Song wrote: > This is similar to commit b21ebf2fb4cde1618915a97cc773e287ff49173e "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, but R_386_PLT32 is arguably preferable for -fno-pic code as well: > this can avoid a "canonical PLT entry" (st_shndx=0, st_value!=0) if the > symbol turns out to be defined externally. Latest Clang (since > 961f31d8ad14c66829991522d73e14b5a96ff6d4) can use R_386_PLT32 for > compiler produced symbols (if we drop -ffreestanding for CONFIG_X86_32, > library call optimization can produce newer declarations) and future GCC > may use R_386_PLT32 as well if the maintainers agree to adopt an option > like -fdirect-access-external-data to avoid "canonical PLT entry"/copy > relocations https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98112 > > Link: https://github.com/ClangBuiltLinux/linux/issues/1210 > Reported-by: Arnd Bergmann <a...@arndb.de> > Signed-off-by: Fangrui Song <mask...@google.com>
I agree with Nick's comments about the commit message. With those addressed: Reviewed-by: Nathan Chancellor <natechancel...@gmail.com> Tested-by: Nathan Chancellor <natechancel...@gmail.com> > --- > 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. > -- > 2.29.2.729.g45daf8777d-goog >
