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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// This test verifies that fork(2) in a signal handler will correctly
// restore floating point state after the signal handler returns in both
// the child and parent.
#include <sys/time.h>
#include "gtest/gtest.h"
#include "test/util/logging.h"
#include "test/util/test_util.h"
#include "test/util/thread_util.h"
namespace gvisor {
namespace testing {
namespace {
#define GET_XMM(__var, __xmm) \
asm volatile("movq %%" #__xmm ", %0" : "=r"(__var))
#define SET_XMM(__var, __xmm) asm volatile("movq %0, %%" #__xmm : : "r"(__var))
int parent, child;
void sigusr1(int s, siginfo_t* siginfo, void* _uc) {
// Fork and clobber %xmm0. The fpstate should be restored by sigreturn(2)
// in both parent and child.
child = fork();
TEST_CHECK_MSG(child >= 0, "fork failed");
uint64_t val = SIGUSR1;
SET_XMM(val, xmm0);
}
TEST(FPSigTest, Fork) {
parent = getpid();
pid_t parent_tid = gettid();
struct sigaction sa = {};
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = sigusr1;
ASSERT_THAT(sigaction(SIGUSR1, &sa, nullptr), SyscallSucceeds());
// The amd64 ABI specifies that the XMM register set is caller-saved. This
// implies that if there is any function call between SET_XMM and GET_XMM the
// compiler might save/restore xmm0 implicitly. This defeats the entire
// purpose of the test which is to verify that fpstate is restored by
// sigreturn(2).
//
// This is the reason why 'tgkill(getpid(), gettid(), SIGUSR1)' is implemented
// in inline assembly below.
//
// If the OS is broken and registers are clobbered by the child, using tgkill
// to signal the current thread increases the likelihood that this thread will
// be the one clobbered.
uint64_t expected = 0xdeadbeeffacefeed;
SET_XMM(expected, xmm0);
asm volatile(
"movl %[killnr], %%eax;"
"movl %[parent], %%edi;"
"movl %[tid], %%esi;"
"movl %[sig], %%edx;"
"syscall;"
:
: [ killnr ] "i"(__NR_tgkill), [ parent ] "rm"(parent),
[ tid ] "rm"(parent_tid), [ sig ] "i"(SIGUSR1)
: "rax", "rdi", "rsi", "rdx",
// Clobbered by syscall.
"rcx", "r11");
uint64_t got;
GET_XMM(got, xmm0);
if (getpid() == parent) { // Parent.
int status;
ASSERT_THAT(waitpid(child, &status, 0), SyscallSucceedsWithValue(child));
EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
}
// TEST_CHECK_MSG since this may run in the child.
TEST_CHECK_MSG(expected == got, "Bad xmm0 value");
if (getpid() != parent) { // Child.
_exit(0);
}
}
} // namespace
} // namespace testing
} // namespace gvisor
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