[PATCH 0/1] MR3117: loader: Set the visibility of symbols in preloader to "hidden". (#55095)
Today, the preloader is linked with -fPIE in spite of the fact that the preloader is a non-PIE statically linked binary. This is due to a limitation in tools/makedep that makes it difficult to specify CFLAGS for each individual object file's recipe. This can seemingly cause problems with some GOTPCREL(X) relocations inside the preloader. Since preloader does not link to the system library directly, there is no need for Global Offset Tables (GOT). However, a few extern (non-static) function symbols are declared, the use of which makes GCC emit instructions that references those symbols by indirection through GOT. The linker then tries to optimize such instructions to eliminate GOT references, which can fail due to various reasons. This stands in contradiction with Jinoh Kang's suggestion (in bug 55050) that "-fPIE is harmless even when applied to an object linked into non-PIE executables." The claim is theoretically true since position-independent code can in principle be relocated to any address (fixed or dynamic); however, it fails due to some peculiar practical issues, which is arguably a limitation in the linker's implementation (since it can be worked around --no-relax without issues). Fix this by eliminating GOT usage by setting the default visibility of non-static declarations to "hidden". Assuming GCC's medium code model (-mcmodel=medium; default code model for x86_64), this suppresses any unnecessary PLT or GOT relocations for defined symbols, and provides opportunity for GCC to optimize the code better. Fixes: 78ed343842dcd8ffb95c416420953e121959d40d Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=55095 cc/ @epo -- https://gitlab.winehq.org/wine/wine/-/merge_requests/3117
From: Jinoh Kang <jinoh.kang.kr(a)gmail.com> Today, the preloader is linked with -fPIE in spite of the fact that the preloader is a non-PIE statically linked binary. This is due to a limitation in tools/makedep that makes it difficult to specify CFLAGS for each individual object file's recipe. This can seemingly cause problems with some GOTPCREL(X) relocations inside the preloader. Since preloader does not link to the system library directly, there is no need for Global Offset Tables (GOT). However, a few extern (non-static) function symbols are declared, the use of which makes GCC emit instructions that references those symbols by indirection through GOT. The linker then tries to optimize such instructions to eliminate GOT references, which can fail due to various reasons. This stands in contradiction with Jinoh Kang's suggestion (in bug 55050) that "-fPIE is harmless even when applied to an object linked into non-PIE executables." The claim is theoretically true since position-independent code can in principle be relocated to any address (fixed or dynamic); however, it fails due to some peculiar practical issues, which is arguably a limitation in the linker's implementation (since it can be worked around --no-relax without issues). Fix this by eliminating GOT usage by setting the default visibility of non-static declarations to "hidden". Assuming GCC's medium code model (-mcmodel=medium; default code model for x86_64), this suppresses any unnecessary PLT or GOT relocations for defined symbols, and provides opportunity for GCC to optimize the code better. Fixes: 78ed343842dcd8ffb95c416420953e121959d40d Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=55095 --- loader/preloader.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/loader/preloader.c b/loader/preloader.c index 4045db64822..635e85ee7cb 100644 --- a/loader/preloader.c +++ b/loader/preloader.c @@ -89,6 +89,8 @@ #include "wine/asm.h" #include "main.h" +#pragma GCC visibility push(hidden) + /* ELF definitions */ #define ELF_PREFERRED_ADDRESS(loader, maplength, mapstartpref) (mapstartpref) #define ELF_FIXED_ADDRESS(loader, mapstart) ((void) 0) @@ -1497,4 +1499,6 @@ void* wld_start( void **stack ) return (void *)ld_so_map.l_entry; } +#pragma GCC visibility pop + #endif /* __linux__ */ -- GitLab https://gitlab.winehq.org/wine/wine/-/merge_requests/3117
v1 -> v2: Fix commit message typos -- https://gitlab.winehq.org/wine/wine/-/merge_requests/3117#note_36276
participants (2)
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Jinoh Kang -
Jinoh Kang (＠iamahuman)