From ea723210a76778c7e86b8df21cb284fc2665ee4f Mon Sep 17 00:00:00 2001 From: mancha Date: Wed, 22 Oct 2014 Subject: Fix unsafe compiler optimization GCC 4.8 enables -ftree-loop-distribute-patterns at -O3 by default and this optimization may transform loops into memset/memmove calls. Without proper handling this may generate unexpected PLT calls on GLIBC. This patch fixes by creating memset/memmove aliases to internal GLIBC __GI_memset/__GI_memmove symbols. This fix for use on glibc 2.17 is based on the following upstream commits: https://sourceware.org/git/?p=glibc.git;h=6a97b62a5b4f https://sourceware.org/git/?p=glibc.git;h=4959e284ca9c --- sysdeps/generic/symbol-hacks.h | 7 ++++++- sysdeps/wordsize-32/symbol-hacks.h | 2 ++ sysdeps/x86_64/x32/symbol-hacks.h | 2 +- 3 files changed, 9 insertions(+), 2 deletions(-) --- a/sysdeps/generic/symbol-hacks.h +++ b/sysdeps/generic/symbol-hacks.h @@ -1 +1,6 @@ -/* Fortunately nothing to do. */ +/* Some compiler optimizations may transform loops into memset/memmove + calls and without proper declaration it may generate PLT calls. */ +#if !defined __ASSEMBLER__ && !defined NOT_IN_libc && defined SHARED +asm ("memmove = __GI_memmove"); +asm ("memset = __GI_memset"); +#endif --- a/sysdeps/wordsize-32/symbol-hacks.h +++ b/sysdeps/wordsize-32/symbol-hacks.h @@ -16,6 +16,8 @@ License along with the GNU C Library; if not, see . */ +#include_next "symbol-hacks.h" + /* A very dirty trick: gcc emits references to __divdi3, __udivdi3, __moddi3, and __umoddi3. These functions are exported and therefore we get PLTs. Unnecessarily so. Changing gcc is a big --- a/sysdeps/x86_64/x32/symbol-hacks.h +++ b/sysdeps/x86_64/x32/symbol-hacks.h @@ -1 +1 @@ -/* Fortunately nothing to do. */ +#include