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commitbb73d07148upstream. This is similar to commitb21ebf2fb4("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=27169a084c0388e[1] [ bp: Massage commit message. ] Reported-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Fangrui Song <maskray@google.com> Signed-off-by: Borislav Petkov <bp@suse.de> 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> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Link: https://lkml.kernel.org/r/20210127205600.1227437-1-maskray@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.