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317f1c0a8a
Crossing 2GB boundaries with indirect calls and jumps can use more branch prediction resources on Intel Golden Cove CPU (see the "Misprediction for Branches >2GB" section in Intel 64 and IA-32 Architectures Optimization Reference Manual.) There is visible performance improvement on workloads with many PLT calls when executable and shared libraries are mmapped below 2GB. Add the Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable or denywrite pages in shared libraries with MAP_32BIT first. NB: 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 the tunable, glibc.cpu.prefer_map_32bit_exec, or the environment variable, LD_PREFER_MAP_32BIT_EXEC. This works only between shared libraries or between shared libraries and executables with addresses below 2GB. PIEs are usually loaded at a random address above 4GB by the kernel.
36 lines
1.2 KiB
Modula-2
36 lines
1.2 KiB
Modula-2
/* Bits in the PREFERRED_FEATURE_INDEX_1 bitfield of <cpu-features.h>.
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Copyright (C) 2020-2023 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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BIT (Fast_Rep_String)
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BIT (Fast_Copy_Backward)
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BIT (Slow_BSF)
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BIT (Fast_Unaligned_Load)
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BIT (Prefer_PMINUB_for_stringop)
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BIT (Fast_Unaligned_Copy)
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BIT (I586)
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BIT (I686)
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BIT (Slow_SSE4_2)
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BIT (AVX_Fast_Unaligned_Load)
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BIT (Prefer_MAP_32BIT_EXEC)
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BIT (Prefer_No_VZEROUPPER)
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BIT (Prefer_ERMS)
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BIT (Prefer_No_AVX512)
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BIT (MathVec_Prefer_No_AVX512)
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BIT (Prefer_FSRM)
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BIT (Avoid_Short_Distance_REP_MOVSB)
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