e949195f64
In order for an ifunc resolver to detect the presence of certain CPU features, access to getauxval(AT_HWCAP) or getauxval(AT_HWCAP2) may be required. In order for getauxval() to work, it needs to access the pointer to the auxiliary vector stored by the linker in the libc shared globals data structure. Accessing the shared globals requires libc to call the __libc_shared_globals() function exported by the linker. However, in order to call this function, libc must be fully relocated, which is not guaranteed to be the case at the point when ifunc resolvers are called. glibc solves this problem by passing the values of getauxval(AT_HWCAP) (and getauxval(AT_HWCAP2) on aarch64) as arguments to the ifunc resolver. Since this seems to be not only the most straightforward way to solve the problem but also improves our compatibility with glibc, we adopt their calling convention. This change is ABI compatible with old resolvers because the arguments are passed in registers, so the old resolvers will simply ignore the new arguments. Bug: 135772972 Change-Id: Ie65bd6e7067f0c878df3d348c815fda61dc12de2
86 lines
1.8 KiB
C++
86 lines
1.8 KiB
C++
/*
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* Copyright (C) 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <gtest/gtest.h>
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#include <sys/auxv.h>
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#if defined(__BIONIC__)
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#include <sys/ifunc.h>
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#endif
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typedef int (*fn_ptr_t)();
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int ret42() {
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return 42;
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}
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extern "C" fn_ptr_t resolver() {
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return ret42;
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}
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int ifunc() __attribute__((ifunc("resolver")));
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TEST(ifunc, function) {
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ASSERT_EQ(42, ifunc());
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}
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#if defined(__BIONIC__)
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#if defined(__aarch64__)
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static uint64_t g_hwcap;
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static __ifunc_arg_t g_arg;
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extern "C" fn_ptr_t hwcap_resolver(uint64_t hwcap, __ifunc_arg_t* arg) {
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g_hwcap = hwcap;
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g_arg = *arg;
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return ret42;
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}
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#elif defined(__arm__)
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static unsigned long g_hwcap;
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extern "C" fn_ptr_t hwcap_resolver(unsigned long hwcap) {
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g_hwcap = hwcap;
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return ret42;
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}
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#else
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extern "C" fn_ptr_t hwcap_resolver() {
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return ret42;
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}
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#endif
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int hwcap() __attribute__((ifunc("hwcap_resolver")));
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TEST(ifunc, hwcap) {
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ASSERT_EQ(42, hwcap());
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#if defined(__aarch64__)
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EXPECT_EQ(getauxval(AT_HWCAP) | _IFUNC_ARG_HWCAP, g_hwcap);
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EXPECT_EQ(sizeof(__ifunc_arg_t), g_arg._size);
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EXPECT_EQ(getauxval(AT_HWCAP), g_arg._hwcap);
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EXPECT_EQ(getauxval(AT_HWCAP2), g_arg._hwcap2);
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#elif defined(__arm__)
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EXPECT_EQ(getauxval(AT_HWCAP), g_hwcap);
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#endif
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}
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#endif // defined(__BIONIC__)
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