diff options
| author | Fangrui Song <[email protected]> | 2021-01-27 12:56:00 -0800 |
|---|---|---|
| committer | Borislav Petkov <[email protected]> | 2021-01-28 12:24:06 +0100 |
| commit | bb73d07148c405c293e576b40af37737faf23a6a (patch) | |
| tree | bf2b8f89ae32db67fd741e426937870e822030ee /net/unix/unix_bpf.c | |
| parent | ac5d08870d0b94cbfa8103c9e294de2b96f249bc (diff) | |
x86/build: Treat R_386_PLT32 relocation as R_386_PC32
This is similar to commit
b21ebf2fb4cd ("x86: Treat R_X86_64_PLT32 as R_X86_64_PC32")
but for i386. As far as the kernel is concerned, R_386_PLT32 can be
treated the same as R_386_PC32.
R_386_PLT32/R_X86_64_PLT32 are PC-relative relocation types which
can only be used by branches. If the referenced symbol is defined
externally, a PLT will be used.
R_386_PC32/R_X86_64_PC32 are PC-relative relocation types which can be
used by address taking operations and branches. If the referenced symbol
is defined externally, a copy relocation/canonical PLT entry will be
created in the executable.
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.
This avoids canonical PLT entries (st_shndx=0, st_value!=0).
On i386, there are 2 types of PLTs, PIC and non-PIC. Currently,
the GCC/GNU as convention is to use R_386_PC32 for non-PIC PLT and
R_386_PLT32 for PIC PLT. Copy relocations/canonical PLT entries
are possible ABI issues but GCC/GNU as will likely keep the status
quo because (1) the ABI is legacy (2) the change will drop a GNU
ld diagnostic for non-default visibility ifunc in shared objects.
clang-12 -fno-pic (since [1]) can emit R_386_PLT32 for compiler
generated function declarations, because preventing canonical PLT
entries is weighed over the rare ifunc diagnostic.
Further info for the more interested:
https://github.com/ClangBuiltLinux/linux/issues/1210
https://sourceware.org/bugzilla/show_bug.cgi?id=27169
https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6 [1]
[ bp: Massage commit message. ]
Reported-by: Arnd Bergmann <[email protected]>
Signed-off-by: Fangrui Song <[email protected]>
Signed-off-by: Borislav Petkov <[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]>
Tested-by: Sedat Dilek <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Diffstat (limited to 'net/unix/unix_bpf.c')
0 files changed, 0 insertions, 0 deletions