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, 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.
clang-12 -fno-pic (since
https://github.com/llvm/llvm-project/commit/961f31d8ad14c66829991522d73e14b5a96ff6d4)
can emit 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 -fno-pic may emit R_386_PLT32 as well
if an option like -fno-direct-access-external-data is adopted to avoid
canonical PLT entry/copy relocations.
Link: https://github.com/ClangBuiltLinux/linux/issues/1210
Link:
https://github.com/llvm/llvm-project/commit/961f31d8ad14c66829991522d73e14b5a96ff6d4
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98112
Reported-by: Arnd Bergmann <[email protected]>
Signed-off-by: Fangrui Song <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
---
Change in v2:
* Improve commit message
---
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
