249757bae2
Using ifuncs allows the linker to select faster versions of libc functions
like strcmp, making linking faster.
The linker continues to first initialize TLS, then call the ifunc
resolvers. There are small amounts of code in Bionic that need to avoid
calling functions selected using ifuncs (generally string.h APIs). I've
tried to compile those pieces with -ffreestanding. Maybe it's unnecessary,
but maybe it could help avoid compiler-inserted memset calls, and maybe
it will be useful later on.
The ifuncs are called in a special early pass using special
__rel[a]_iplt_start / __rel[a]_iplt_end symbols. The linker will encounter
the ifuncs again as R_*_IRELATIVE dynamic relocations, so they're skipped
on the second pass.
Break linker_main.cpp into its own liblinker_main library so it can be
compiled with -ffreestanding.
On walleye, this change fixes a recent 2.3% linker64 start-up time
regression (156.6ms -> 160.2ms), but it also helps the 32-bit time by
about 1.9% on the same benchmark. I'm measuring the run-time using a
synthetic benchmark based on loading libandroid_servers.so.
Test: bionic unit tests, manual benchmarking
Bug: none
Merged-In: Ieb9446c2df13a66fc0d377596756becad0af6995
Change-Id: Ieb9446c2df13a66fc0d377596756becad0af6995
(cherry picked from commit 772bcbb0c2)
64 lines
2.6 KiB
C++
64 lines
2.6 KiB
C++
/*
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* Copyright (C) 2019 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "private/bionic_call_ifunc_resolver.h"
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#include <sys/auxv.h>
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#include <sys/ifunc.h>
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#include "private/bionic_auxv.h"
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// This code is called in the linker before it has been relocated, so minimize calls into other
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// parts of Bionic. In particular, we won't ever have two ifunc resolvers called concurrently, so
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// initializing the ifunc resolver argument doesn't need to be thread-safe.
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ElfW(Addr) __bionic_call_ifunc_resolver(ElfW(Addr) resolver_addr) {
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#if defined(__aarch64__)
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typedef ElfW(Addr) (*ifunc_resolver_t)(uint64_t, __ifunc_arg_t*);
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static __ifunc_arg_t arg;
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static bool initialized = false;
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if (!initialized) {
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initialized = true;
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arg._size = sizeof(__ifunc_arg_t);
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arg._hwcap = getauxval(AT_HWCAP);
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arg._hwcap2 = getauxval(AT_HWCAP2);
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}
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return reinterpret_cast<ifunc_resolver_t>(resolver_addr)(arg._hwcap | _IFUNC_ARG_HWCAP, &arg);
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#elif defined(__arm__)
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typedef ElfW(Addr) (*ifunc_resolver_t)(unsigned long);
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static unsigned long hwcap;
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static bool initialized = false;
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if (!initialized) {
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initialized = true;
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hwcap = getauxval(AT_HWCAP);
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}
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return reinterpret_cast<ifunc_resolver_t>(resolver_addr)(hwcap);
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#else
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typedef ElfW(Addr) (*ifunc_resolver_t)(void);
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return reinterpret_cast<ifunc_resolver_t>(resolver_addr)();
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#endif
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}
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