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new abc5595a fix: preserve XMM6-XMM15 in x86_64 bthread context switch
(#3495)
abc5595a is described below
commit abc5595a8abf482c48aaa867a31505d547a73665
Author: Chuang Zhang <[email protected]>
AuthorDate: Fri Sep 18 17:33:32 2026 +0800
fix: preserve XMM6-XMM15 in x86_64 bthread context switch (#3495)
* Fix clang (#28)
Co-authored-by: LinQuickDev <[email protected]>
* fix: preserve SSE state in x86_64 bthread context switch (#31)
---------
Co-authored-by: LinQuickDev <[email protected]>
Co-authored-by: Spicy-cream <[email protected]>
---
src/bthread/context.cpp | 42 ++++++++++----
src/bthread/task_tracer.cpp | 23 +++++++-
test/bthread_context_unittest.cpp | 112 ++++++++++++++++++++++++++++++++++++++
3 files changed, 163 insertions(+), 14 deletions(-)
diff --git a/src/bthread/context.cpp b/src/bthread/context.cpp
index 7f913adf..467445c9 100644
--- a/src/bthread/context.cpp
+++ b/src/bthread/context.cpp
@@ -347,20 +347,40 @@ __asm (
" pushq %r14 \n"
" pushq %r13 \n"
" pushq %r12 \n"
-" leaq -0x8(%rsp), %rsp\n"
+" leaq -0xa8(%rsp), %rsp\n"
+" movups %xmm6, 0x00(%rsp)\n"
+" movups %xmm7, 0x10(%rsp)\n"
+" movups %xmm8, 0x20(%rsp)\n"
+" movups %xmm9, 0x30(%rsp)\n"
+" movups %xmm10, 0x40(%rsp)\n"
+" movups %xmm11, 0x50(%rsp)\n"
+" movups %xmm12, 0x60(%rsp)\n"
+" movups %xmm13, 0x70(%rsp)\n"
+" movups %xmm14, 0x80(%rsp)\n"
+" movups %xmm15, 0x90(%rsp)\n"
" cmp $0, %rcx\n"
" je 1f\n"
-" stmxcsr (%rsp)\n"
-" fnstcw 0x4(%rsp)\n"
+" stmxcsr 0xa0(%rsp)\n"
+" fnstcw 0xa4(%rsp)\n"
"1:\n"
" movq %rsp, (%rdi)\n"
" movq %rsi, %rsp\n"
+" movups 0x00(%rsp), %xmm6\n"
+" movups 0x10(%rsp), %xmm7\n"
+" movups 0x20(%rsp), %xmm8\n"
+" movups 0x30(%rsp), %xmm9\n"
+" movups 0x40(%rsp), %xmm10\n"
+" movups 0x50(%rsp), %xmm11\n"
+" movups 0x60(%rsp), %xmm12\n"
+" movups 0x70(%rsp), %xmm13\n"
+" movups 0x80(%rsp), %xmm14\n"
+" movups 0x90(%rsp), %xmm15\n"
" cmp $0, %rcx\n"
" je 2f\n"
-" ldmxcsr (%rsp)\n"
-" fldcw 0x4(%rsp)\n"
+" ldmxcsr 0xa0(%rsp)\n"
+" fldcw 0xa4(%rsp)\n"
"2:\n"
-" leaq 0x8(%rsp), %rsp\n"
+" leaq 0xa8(%rsp), %rsp\n"
" popq %r12 \n"
" popq %r13 \n"
" popq %r14 \n"
@@ -387,12 +407,12 @@ __asm (
"bthread_make_fcontext:\n"
" movq %rdi, %rax\n"
" andq $-16, %rax\n"
-" leaq -0x48(%rax), %rax\n"
-" movq %rdx, 0x38(%rax)\n"
-" stmxcsr (%rax)\n"
-" fnstcw 0x4(%rax)\n"
+" leaq -0xe8(%rax), %rax\n"
+" movq %rdx, 0xd8(%rax)\n"
+" stmxcsr 0xa0(%rax)\n"
+" fnstcw 0xa4(%rax)\n"
" leaq finish(%rip), %rcx\n"
-" movq %rcx, 0x40(%rax)\n"
+" movq %rcx, 0xe0(%rax)\n"
" ret \n"
"finish:\n"
" xorq %rdi, %rdi\n"
diff --git a/src/bthread/task_tracer.cpp b/src/bthread/task_tracer.cpp
index 1cc5c05a..031ad793 100644
--- a/src/bthread/task_tracer.cpp
+++ b/src/bthread/task_tracer.cpp
@@ -35,6 +35,23 @@
namespace bthread {
+namespace {
+
+// These slots must match the Linux x86_64 frame built by
+// bthread_jump_fcontext in context.cpp. XMM6-XMM15 add 10 128-bit values,
+// or 20 uintptr_t slots, ahead of the previously saved registers.
+constexpr size_t kSavedXmmRegisterCount = 10;
+constexpr size_t kSavedXmmRegisterBytes = 16;
+constexpr size_t kSavedXmmRegisterSlots =
+ kSavedXmmRegisterCount * kSavedXmmRegisterBytes / sizeof(uintptr_t);
+constexpr size_t kRbpContextSlot = 6 + kSavedXmmRegisterSlots;
+constexpr size_t kRipContextSlot = 7 + kSavedXmmRegisterSlots;
+#if UNW_VERSION_MAJOR >= 1 && UNW_VERSION_MINOR >= 7
+constexpr size_t kRspContextSlot = 8 + kSavedXmmRegisterSlots;
+#endif
+
+} // namespace
+
DEFINE_uint32(signal_trace_timeout_ms, 50, "Timeout for signal trace in ms");
BUTIL_VALIDATE_GFLAG(signal_trace_timeout_ms,
butil::PositiveInteger<uint32_t>);
// Note that SIGURG handler may be registered by some library such as cgo
@@ -280,16 +297,16 @@ unw_cursor_t TaskTracer::MakeCursor(bthread_fcontext_t
fcontext) {
// Only need RBP, RIP, RSP on x86_64.
// The base pointer (RBP).
- if (unw_set_reg(&cursor, UNW_X86_64_RBP, regs[6]) != 0) {
+ if (unw_set_reg(&cursor, UNW_X86_64_RBP, regs[kRbpContextSlot]) != 0) {
LOG(ERROR) << "Fail to set RBP";
}
// The instruction pointer (RIP).
- if (unw_set_reg(&cursor, UNW_REG_IP, regs[7]) != 0) {
+ if (unw_set_reg(&cursor, UNW_REG_IP, regs[kRipContextSlot]) != 0) {
LOG(ERROR) << "Fail to set RIP";
}
#if UNW_VERSION_MAJOR >= 1 && UNW_VERSION_MINOR >= 7
// The stack pointer (RSP).
- if (unw_set_reg(&cursor, UNW_REG_SP, regs[8]) != 0) {
+ if (unw_set_reg(&cursor, UNW_REG_SP, regs[kRspContextSlot]) != 0) {
LOG(ERROR) << "Fail to set RSP";
}
#endif
diff --git a/test/bthread_context_unittest.cpp
b/test/bthread_context_unittest.cpp
new file mode 100644
index 00000000..ff4a2f69
--- /dev/null
+++ b/test/bthread_context_unittest.cpp
@@ -0,0 +1,112 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you 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.
+
+#include <gtest/gtest.h>
+
+#include <cstdint>
+#include <cstdlib>
+#include <cstring>
+
+#include "bthread/context.h"
+
+#if defined(BTHREAD_CONTEXT_PLATFORM_linux_x86_64)
+
+namespace {
+
+constexpr size_t kStackSize = 8192;
+constexpr size_t kXmmRegisterCount = 10;
+
+struct XmmState {
+ uint8_t registers[kXmmRegisterCount][16];
+};
+
+bthread_fcontext_t g_main_context;
+bthread_fcontext_t g_test_context;
+XmmState g_clobber_state;
+
+extern "C" intptr_t jump_with_xmm_state(
+ bthread_fcontext_t* old_context, bthread_fcontext_t new_context,
+ intptr_t value, const XmmState* input, XmmState* output);
+
+// Keep the register setup, context switch, and register capture in one
+// assembly function so the compiler cannot use an XMM register between them.
+__asm__(
+".text\n"
+".p2align 4,,15\n"
+".type jump_with_xmm_state,@function\n"
+"jump_with_xmm_state:\n"
+" movups 0x00(%rcx), %xmm6\n"
+" movups 0x10(%rcx), %xmm7\n"
+" movups 0x20(%rcx), %xmm8\n"
+" movups 0x30(%rcx), %xmm9\n"
+" movups 0x40(%rcx), %xmm10\n"
+" movups 0x50(%rcx), %xmm11\n"
+" movups 0x60(%rcx), %xmm12\n"
+" movups 0x70(%rcx), %xmm13\n"
+" movups 0x80(%rcx), %xmm14\n"
+" movups 0x90(%rcx), %xmm15\n"
+" pushq %r8\n"
+" xorl %ecx, %ecx\n"
+" call bthread_jump_fcontext\n"
+" popq %r8\n"
+" movups %xmm6, 0x00(%r8)\n"
+" movups %xmm7, 0x10(%r8)\n"
+" movups %xmm8, 0x20(%r8)\n"
+" movups %xmm9, 0x30(%r8)\n"
+" movups %xmm10, 0x40(%r8)\n"
+" movups %xmm11, 0x50(%r8)\n"
+" movups %xmm12, 0x60(%r8)\n"
+" movups %xmm13, 0x70(%r8)\n"
+" movups %xmm14, 0x80(%r8)\n"
+" movups %xmm15, 0x90(%r8)\n"
+" ret\n"
+".size jump_with_xmm_state,.-jump_with_xmm_state\n");
+
+void overwrite_xmm_and_return(intptr_t) {
+ XmmState ignored = {};
+ jump_with_xmm_state(&g_test_context, g_main_context, 0,
+ &g_clobber_state, &ignored);
+}
+
+TEST(BthreadContextTest, preserves_xmm6_through_xmm15) {
+ XmmState expected;
+ XmmState actual = {};
+ for (size_t reg = 0; reg < kXmmRegisterCount; ++reg) {
+ for (size_t byte = 0; byte < 16; ++byte) {
+ expected.registers[reg][byte] =
+ static_cast<uint8_t>(reg * 16 + byte);
+ g_clobber_state.registers[reg][byte] =
+ static_cast<uint8_t>(0xff - reg * 16 - byte);
+ }
+ }
+
+ void* stack = std::malloc(kStackSize);
+ ASSERT_NE(nullptr, stack);
+ g_main_context = nullptr;
+ g_test_context = bthread_make_fcontext(
+ static_cast<char*>(stack) + kStackSize, kStackSize,
+ overwrite_xmm_and_return);
+
+ jump_with_xmm_state(&g_main_context, g_test_context, 0, &expected,
&actual);
+
+ EXPECT_EQ(0, std::memcmp(&expected, &actual, sizeof(expected)));
+ std::free(stack);
+}
+
+} // namespace
+
+#endif // BTHREAD_CONTEXT_PLATFORM_linux_x86_64
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