1 files changed, 134 insertions, 0 deletions
diff --git a/test/syscalls/linux/fpsig_nested.cc b/test/syscalls/linux/fpsig_nested.cc
new file mode 100644
index 000000000..2fa40b42d
--- /dev/null
+++ b/test/syscalls/linux/fpsig_nested.cc
@@ -0,0 +1,134 @@
+// Copyright 2018 Google LLC
+//
+// 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 program verifies that application floating point state is restored
+// correctly after a signal handler returns. It also verifies that this works
+// with nested signals.
+#include <sys/time.h>
+
+#include "gtest/gtest.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 pid;
+int tid;
+
+volatile uint64_t entryxmm[2] = {~0UL, ~0UL};
+volatile uint64_t exitxmm[2];
+
+void sigusr2(int s, siginfo_t* siginfo, void* _uc) {
+  uint64_t val = SIGUSR2;
+
+  // Record the value of %xmm0 on entry and then clobber it.
+  GET_XMM(entryxmm[1], xmm0);
+  SET_XMM(val, xmm0);
+  GET_XMM(exitxmm[1], xmm0);
+}
+
+void sigusr1(int s, siginfo_t* siginfo, void* _uc) {
+  uint64_t val = SIGUSR1;
+
+  // Record the value of %xmm0 on entry and then clobber it.
+  GET_XMM(entryxmm[0], xmm0);
+  SET_XMM(val, xmm0);
+
+  // Send a SIGUSR2 to ourself. The signal mask is configured such that
+  // the SIGUSR2 handler will run before this handler returns.
+  asm volatile(
+      "movl %[killnr], %%eax;"
+      "movl %[pid], %%edi;"
+      "movl %[tid], %%esi;"
+      "movl %[sig], %%edx;"
+      "syscall;"
+      :
+      : [killnr] "i"(__NR_tgkill), [pid] "rm"(pid), [tid] "rm"(tid),
+        [sig] "i"(SIGUSR2)
+      : "rax", "rdi", "rsi", "rdx",
+        // Clobbered by syscall.
+        "rcx", "r11");
+
+  // Record value of %xmm0 again to verify that the nested signal handler
+  // does not clobber it.
+  GET_XMM(exitxmm[0], xmm0);
+}
+
+TEST(FPSigTest, NestedSignals) {
+  pid = getpid();
+  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());
+
+  sa.sa_sigaction = sigusr2;
+  ASSERT_THAT(sigaction(SIGUSR2, &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 signal, using tgkill
+  // to signal the current thread ensures that this is the clobbered thread.
+
+  uint64_t expected = 0xdeadbeeffacefeed;
+  SET_XMM(expected, xmm0);
+
+  asm volatile(
+      "movl %[killnr], %%eax;"
+      "movl %[pid], %%edi;"
+      "movl %[tid], %%esi;"
+      "movl %[sig], %%edx;"
+      "syscall;"
+      :
+      : [killnr] "i"(__NR_tgkill), [pid] "rm"(pid), [tid] "rm"(tid),
+        [sig] "i"(SIGUSR1)
+      : "rax", "rdi", "rsi", "rdx",
+        // Clobbered by syscall.
+        "rcx", "r11");
+
+  uint64_t got;
+  GET_XMM(got, xmm0);
+
+  //
+  // The checks below verifies the following:
+  // - signal handlers must called with a clean fpu state.
+  // - sigreturn(2) must restore fpstate of the interrupted context.
+  //
+  EXPECT_EQ(expected, got);
+  EXPECT_EQ(entryxmm[0], 0);
+  EXPECT_EQ(entryxmm[1], 0);
+  EXPECT_EQ(exitxmm[0], SIGUSR1);
+  EXPECT_EQ(exitxmm[1], SIGUSR2);
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor