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2a969b53c0
The tunable parsing duplicates the tunable environment variable so it null-terminates each one since it simplifies the later parsing. It has the drawback of adding another point of failure (__minimal_malloc failing), and the memory copy requires tuning the compiler to avoid mem operations calls. The parsing now tracks the tunable start and its size. The dl-tunable-parse.h adds helper functions to help parsing, like a strcmp that also checks for size and an iterator for suboptions that are comma-separated (used on hwcap parsing by x86, powerpc, and s390x). Since the environment variable is allocated on the stack by the kernel, it is safe to keep the references to the suboptions for later parsing of string tunables (as done by set_hwcaps by multiple architectures). Checked on x86_64-linux-gnu, powerpc64le-linux-gnu, and aarch64-linux-gnu. Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
105 lines
3.7 KiB
C
105 lines
3.7 KiB
C
/* Initialize cpu feature data. PowerPC version.
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Copyright (C) 2017-2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <array_length.h>
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#include <stdint.h>
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#include <cpu-features.h>
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#include <elf/dl-tunables.h>
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#include <dl-tunables-parse.h>
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#include <unistd.h>
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#include <string.h>
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static void
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TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
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{
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/* The current IFUNC selection is always using the most recent
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features which are available via AT_HWCAP or AT_HWCAP2. But in
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some scenarios it is useful to adjust this selection.
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The environment variable:
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GLIBC_TUNABLES=glibc.cpu.hwcaps=-xxx,yyy,....
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Can be used to enable HWCAP/HWCAP2 feature yyy, disable HWCAP/HWCAP2
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feature xxx, where the feature name is case-sensitive and has to match
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the ones mentioned in the file{sysdeps/powerpc/dl-procinfo.c}. */
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/* Copy the features from dl_powerpc_cpu_features, which contains the
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features provided by AT_HWCAP and AT_HWCAP2. */
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struct cpu_features *cpu_features = &GLRO(dl_powerpc_cpu_features);
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unsigned long int tcbv_hwcap = cpu_features->hwcap;
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unsigned long int tcbv_hwcap2 = cpu_features->hwcap2;
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struct tunable_str_comma_state_t ts;
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tunable_str_comma_init (&ts, valp);
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struct tunable_str_comma_t t;
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while (tunable_str_comma_next (&ts, &t))
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{
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if (t.len == 0)
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continue;
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size_t offset = 0;
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for (int i = 0; i < array_length (hwcap_tunables); ++i)
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{
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const char *hwcap_name = hwcap_names + offset;
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size_t hwcap_name_len = strlen (hwcap_name);
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/* Check the tunable name on the supported list. */
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if (tunable_str_comma_strcmp (&t, hwcap_name, hwcap_name_len))
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{
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/* Update the hwcap and hwcap2 bits. */
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if (t.disable)
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{
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/* Id is 1 for hwcap2 tunable. */
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if (hwcap_tunables[i].id)
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cpu_features->hwcap2 &= ~(hwcap_tunables[i].mask);
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else
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cpu_features->hwcap &= ~(hwcap_tunables[i].mask);
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}
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else
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{
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/* Enable the features and also check that no unsupported
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features were enabled by user. */
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if (hwcap_tunables[i].id)
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cpu_features->hwcap2 |= (tcbv_hwcap2 & hwcap_tunables[i].mask);
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else
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cpu_features->hwcap |= (tcbv_hwcap & hwcap_tunables[i].mask);
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}
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break;
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}
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offset += hwcap_name_len + 1;
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}
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}
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}
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static inline void
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init_cpu_features (struct cpu_features *cpu_features, uint64_t hwcaps[])
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{
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/* Fill the cpu_features with the supported hwcaps
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which are set by __tcb_parse_hwcap_and_convert_at_platform. */
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cpu_features->hwcap = hwcaps[0];
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cpu_features->hwcap2 = hwcaps[1];
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/* Default is to use aligned memory access on optimized function unless
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tunables is enable, since for this case user can explicit disable
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unaligned optimizations. */
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int32_t cached_memfunc = TUNABLE_GET (glibc, cpu, cached_memopt, int32_t,
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NULL);
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cpu_features->use_cached_memopt = (cached_memfunc > 0);
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TUNABLE_GET (glibc, cpu, hwcaps, tunable_val_t *,
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TUNABLE_CALLBACK (set_hwcaps));
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}
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