commit b9eb92ab05204df772eb4929eccd018637c9f3e9 Author: H.J. Lu Date: Wed Oct 21 14:44:23 2015 -0700 Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT According to Silvermont software optimization guide, for 64-bit applications, branch prediction performance can be negatively impacted when the target of a branch is more than 4GB away from the branch. Add the Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB, not lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available for address space layout randomization (ASLR), which is always disabled for SUID programs and can only be enabled by setting environment variable, LD_PREFER_MAP_32BIT_EXEC. On Fedora 23, this patch speeds up GCC 5 testsuite by 3% on Silvermont. [BZ #19367] * sysdeps/unix/sysv/linux/wordsize-64/mmap.c: New file. * sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h: Likewise. * sysdeps/unix/sysv/linux/x86_64/64/mmap.c: Likewise. * sysdeps/x86/cpu-features.h (bit_Prefer_MAP_32BIT_EXEC): New. (index_Prefer_MAP_32BIT_EXEC): Likewise. Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/wordsize-64/mmap.c =================================================================== --- /dev/null +++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/wordsize-64/mmap.c @@ -0,0 +1,40 @@ +/* Linux mmap system call. 64-bit version. + Copyright (C) 2015 Free Software Foundation, Inc. + + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include +#include +#include + +/* An architecture may override this. */ +#ifndef MMAP_PREPARE +# define MMAP_PREPARE(addr, len, prot, flags, fd, offset) +#endif + +__ptr_t +__mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset) +{ + MMAP_PREPARE (addr, len, prot, flags, fd, offset); + return (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot, flags, + fd, offset); +} + +weak_alias (__mmap, mmap) +weak_alias (__mmap, mmap64) +weak_alias (__mmap, __mmap64) Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h =================================================================== --- /dev/null +++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h @@ -0,0 +1,44 @@ +/* Optional code to distinguish library flavours. x86-64 version. + Copyright (C) 2015 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#ifndef _DL_LIBRECON_H + +#include + +/* Recognizing extra environment variables. For 64-bit applications, + branch prediction performance may be negatively impacted when the + target of a branch is more than 4GB away from the branch. Add the + Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable + pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB, + not lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available + for address space layout randomization (ASLR). Prefer_MAP_32BIT_EXEC + is always disabled for SUID programs and can be enabled by setting + environment variable, LD_PREFER_MAP_32BIT_EXEC. */ +#define EXTRA_LD_ENVVARS \ + case 21: \ + if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \ + GLRO(dl_x86_cpu_features).feature[index_Prefer_MAP_32BIT_EXEC] \ + = bit_Prefer_MAP_32BIT_EXEC; \ + break; + +/* Extra unsecure variables. The names are all stuffed in a single + string which means they have to be terminated with a '\0' explicitly. */ +#define EXTRA_UNSECURE_ENVVARS \ + "LD_PREFER_MAP_32BIT_EXEC\0" + +#endif /* dl-librecon.h */ Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/mmap.c =================================================================== --- /dev/null +++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/mmap.c @@ -0,0 +1,37 @@ +/* Linux mmap system call. x86-64 version. + Copyright (C) 2015 Free Software Foundation, Inc. + + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include + +/* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages + with MAP_32BIT first. */ +#define MMAP_PREPARE(addr, len, prot, flags, fd, offset) \ + if ((addr) == NULL \ + && ((prot) & PROT_EXEC) != 0 \ + && HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC)) \ + { \ + __ptr_t ret = (__ptr_t) INLINE_SYSCALL (mmap, 6, (addr), (len), \ + (prot), \ + (flags) | MAP_32BIT, \ + (fd), (offset)); \ + if (ret != MAP_FAILED) \ + return ret; \ + } + +#include Index: glibc-2.17-c758a686/sysdeps/x86/cpu-features.h =================================================================== --- glibc-2.17-c758a686.orig/sysdeps/x86/cpu-features.h +++ glibc-2.17-c758a686/sysdeps/x86/cpu-features.h @@ -32,6 +32,7 @@ #define bit_AVX_Fast_Unaligned_Load (1 << 11) #define bit_AVX512F_Usable (1 << 12) #define bit_AVX512DQ_Usable (1 << 13) +#define bit_Prefer_MAP_32BIT_EXEC (1 << 16) /* CPUID Feature flags. */ @@ -91,6 +92,7 @@ # define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1*FEATURE_SIZE # define index_AVX512F_Usable FEATURE_INDEX_1*FEATURE_SIZE # define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE +# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1*FEATURE_SIZE # if defined (_LIBC) && !IS_IN (nonlib) # ifdef __x86_64__ @@ -267,6 +269,7 @@ extern const struct cpu_features *__get_ # define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1 # define index_AVX512F_Usable FEATURE_INDEX_1 # define index_AVX512DQ_Usable FEATURE_INDEX_1 +# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1 #endif /* !__ASSEMBLER__ */