| Message ID | 1496347928-19432-5-git-send-email-siddhesh@sourceware.org |
|---|---|
| State | New |
| Headers | show |
On 01/06/2017 17:12, Siddhesh Poyarekar wrote: > Now that LD_HWCAP_MASK (or glibc.tune.hwcap_mask) is read early enough > to influence cpu feature check in aarch64, use it to influence > multiarch selection. Setting LD_HWCAP_MASK such that it clears > HWCAP_CPUID will now disable multiarch for the binary. > > HWCAP_CPUID is also now set in HWCAP_IMPORTANT so that it is set by > default. With this patch, this feature is only usable with > dyanmically linked binaries because LD_HWCAP_MASK is not read for > static binaries. A future patch fixes that. > > * sysdeps/unix/sysv/linux/aarch64/cpu-features.c > (init_cpu_features): Use glibc.tune.hwcap_mask. > * sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h: New file. LGTM.
On 01/06/17 21:12, Siddhesh Poyarekar wrote: > Now that LD_HWCAP_MASK (or glibc.tune.hwcap_mask) is read early enough > to influence cpu feature check in aarch64, use it to influence > multiarch selection. Setting LD_HWCAP_MASK such that it clears > HWCAP_CPUID will now disable multiarch for the binary. > > HWCAP_CPUID is also now set in HWCAP_IMPORTANT so that it is set by > default. With this patch, this feature is only usable with > dyanmically linked binaries because LD_HWCAP_MASK is not read for > static binaries. A future patch fixes that. > > * sysdeps/unix/sysv/linux/aarch64/cpu-features.c > (init_cpu_features): Use glibc.tune.hwcap_mask. > * sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h: New file. > --- > sysdeps/unix/sysv/linux/aarch64/cpu-features.c | 10 +++--- > sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h | 44 ++++++++++++++++++++++++++ > 2 files changed, 50 insertions(+), 4 deletions(-) > create mode 100644 sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h > OK if the new HWCAP_IMPORTANT does not cause additional open/stat/.. syscalls (please verify that the lib search path is not increased by running something like strace -E LD_PRELOAD=foobar.so /bin/true and counting the failed syscalls) (if the search path is increased then i'd like to know what is the purpose of that feature)
On Wednesday 07 June 2017 08:30 PM, Szabolcs Nagy wrote: > OK if the new HWCAP_IMPORTANT does not cause > additional open/stat/.. syscalls (please verify > that the lib search path is not increased by > running something like > strace -E LD_PRELOAD=foobar.so /bin/true > and counting the failed syscalls) > > (if the search path is increased then i'd like > to know what is the purpose of that feature) I thought I already explained it in a previous email - this adds an additional search path for the dynamic linker to look for libraries that may be optimized for that specific hwcap bit. A straightforward way to disable this is to set LD_HWCAP_MASK to 0x0 to clear hwcap bits. On server systems where this would be used, this would have been done by ldconfig and hence the lookup will not involve a full search every time, just for situations where the library is not mapped into ld.so.cache. Siddhesh
diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c index 7025062..ef6eecd 100644 --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c @@ -18,18 +18,20 @@ #include <cpu-features.h> #include <sys/auxv.h> +#include <elf/dl-hwcaps.h> static inline void init_cpu_features (struct cpu_features *cpu_features) { - if (GLRO(dl_hwcap) & HWCAP_CPUID) + uint64_t hwcap_mask = GET_HWCAP_MASK(); + uint64_t hwcap = GLRO (dl_hwcap) & hwcap_mask; + + if (hwcap & HWCAP_CPUID) { register uint64_t id = 0; asm volatile ("mrs %0, midr_el1" : "=r"(id)); cpu_features->midr_el1 = id; } else - { - cpu_features->midr_el1 = 0; - } + cpu_features->midr_el1 = 0; } diff --git a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h new file mode 100644 index 0000000..7a60d72 --- /dev/null +++ b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h @@ -0,0 +1,44 @@ +/* Processor capability information handling macros - aarch64 version. + Copyright (C) 2017 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 + <http://www.gnu.org/licenses/>. */ + +#ifndef _DL_PROCINFO_H +#define _DL_PROCINFO_H 1 + +#include <sys/auxv.h> + +/* We cannot provide a general printing function. */ +#define _dl_procinfo(type, word) -1 + +/* There are no hardware capabilities defined. */ +#define _dl_hwcap_string(idx) "" + +/* HWCAP_CPUID should be available by default to influence IFUNC as well as + library search. */ +#define HWCAP_IMPORTANT HWCAP_CPUID + +/* There're no platforms to filter out. */ +#define _DL_HWCAP_PLATFORM 0 + +/* We don't have any hardware capabilities. */ +#define _DL_HWCAP_COUNT 0 + +#define _dl_string_hwcap(str) (-1) + +#define _dl_string_platform(str) (-1) + +#endif /* dl-procinfo.h */