[compiler-rt] 9ee61cf - [XRay][x86_64] Fix CFI directives in assembly trampolines
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Wed Mar 3 10:01:33 PST 2021
Author: Elia Geretto
Date: 2021-03-03T10:01:28-08:00
New Revision: 9ee61cf3f67b9fdcee7c2dd650321264376bc0f2
URL: https://github.com/llvm/llvm-project/commit/9ee61cf3f67b9fdcee7c2dd650321264376bc0f2
DIFF: https://github.com/llvm/llvm-project/commit/9ee61cf3f67b9fdcee7c2dd650321264376bc0f2.diff
LOG: [XRay][x86_64] Fix CFI directives in assembly trampolines
This patch modifies the x86_64 XRay trampolines to fix the CFI information
generated by the assembler. One of the main issues in correcting the CFI
directives is the `ALIGNED_CALL_RAX` macro, which makes the CFA dependent on
the alignment of the stack. However, this macro is not really necessary because
some additional assumptions can be made on the alignment of the stack when the
trampolines are called. The code has been written as if the stack is guaranteed
to be 8-bytes aligned; however, it is instead guaranteed to be misaligned by 8
bytes with respect to a 16-bytes alignment. For this reason, always moving the
stack pointer by 8 bytes is sufficient to restore the appropriate alignment.
Trampolines that are called from within a function as a result of the builtins
`__xray_typedevent` and `__xray_customevent` are necessarely called with the
stack properly aligned so, in this case too, `ALIGNED_CALL_RAX` can be
eliminated.
Fixes: https://bugs.llvm.org/show_bug.cgi?id=49060
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D96785
Added:
Modified:
compiler-rt/lib/xray/xray_trampoline_x86_64.S
Removed:
################################################################################
diff --git a/compiler-rt/lib/xray/xray_trampoline_x86_64.S b/compiler-rt/lib/xray/xray_trampoline_x86_64.S
index 12c5a6ccd9a4..530d2ec8602b 100644
--- a/compiler-rt/lib/xray/xray_trampoline_x86_64.S
+++ b/compiler-rt/lib/xray/xray_trampoline_x86_64.S
@@ -15,12 +15,29 @@
#include "../builtins/assembly.h"
#include "../sanitizer_common/sanitizer_asm.h"
+// XRay trampolines which are not produced by intrinsics are not System V AMD64
+// ABI compliant because they are called with a stack that is always misaligned
+// by 8 bytes with respect to a 16 bytes alignment. This is because they are
+// called immediately after the call to, or immediately before returning from,
+// the function being instrumented. This saves space in the patch point, but
+// misaligns the stack by 8 bytes.
+
+.macro ALIGN_STACK_16B
+ subq $8, %rsp
+ CFI_ADJUST_CFA_OFFSET(8)
+.endm
+.macro RESTORE_STACK_ALIGNMENT
+ addq $8, %rsp
+ CFI_ADJUST_CFA_OFFSET(-8)
+.endm
+// This macro should keep the stack aligned to 16 bytes.
.macro SAVE_REGISTERS
pushfq
+ CFI_ADJUST_CFA_OFFSET(8)
subq $240, %rsp
- CFI_DEF_CFA_OFFSET(248)
+ CFI_ADJUST_CFA_OFFSET(240)
movq %rbp, 232(%rsp)
movupd %xmm0, 216(%rsp)
movupd %xmm1, 200(%rsp)
@@ -45,6 +62,7 @@
movq %r15, 0(%rsp)
.endm
+// This macro should keep the stack aligned to 16 bytes.
.macro RESTORE_REGISTERS
movq 232(%rsp), %rbp
movupd 216(%rsp), %xmm0
@@ -69,22 +87,9 @@
movq 8(%rsp), %r14
movq 0(%rsp), %r15
addq $240, %rsp
+ CFI_ADJUST_CFA_OFFSET(-240)
popfq
- CFI_DEF_CFA_OFFSET(8)
-.endm
-
-.macro ALIGNED_CALL_RAX
- // Call the logging handler, after aligning the stack to a 16-byte boundary.
- // The approach we're taking here uses additional stack space to stash the
- // stack pointer twice before aligning the pointer to 16-bytes. If the stack
- // was 8-byte aligned, it will become 16-byte aligned -- when restoring the
- // pointer, we can always look -8 bytes from the current position to get
- // either of the values we've stashed in the first place.
- pushq %rsp
- pushq (%rsp)
- andq $-0x10, %rsp
- callq *%rax
- movq 8(%rsp), %rsp
+ CFI_ADJUST_CFA_OFFSET(-8)
.endm
.text
@@ -104,6 +109,7 @@
# LLVM-MCA-BEGIN __xray_FunctionEntry
ASM_SYMBOL(__xray_FunctionEntry):
CFI_STARTPROC
+ ALIGN_STACK_16B
SAVE_REGISTERS
// This load has to be atomic, it's concurrent with __xray_patch().
@@ -115,10 +121,11 @@ ASM_SYMBOL(__xray_FunctionEntry):
// The patched function prologue puts its xray_instr_map index into %r10d.
movl %r10d, %edi
xor %esi,%esi
- ALIGNED_CALL_RAX
+ callq *%rax
.Ltmp0:
RESTORE_REGISTERS
+ RESTORE_STACK_ALIGNMENT
retq
# LLVM-MCA-END
ASM_SIZE(__xray_FunctionEntry)
@@ -133,11 +140,13 @@ ASM_SYMBOL(__xray_FunctionEntry):
# LLVM-MCA-BEGIN __xray_FunctionExit
ASM_SYMBOL(__xray_FunctionExit):
CFI_STARTPROC
+ ALIGN_STACK_16B
+
// Save the important registers first. Since we're assuming that this
// function is only jumped into, we only preserve the registers for
// returning.
- subq $56, %rsp
- CFI_DEF_CFA_OFFSET(64)
+ subq $64, %rsp
+ CFI_ADJUST_CFA_OFFSET(64)
movq %rbp, 48(%rsp)
movupd %xmm0, 32(%rsp)
movupd %xmm1, 16(%rsp)
@@ -149,7 +158,7 @@ ASM_SYMBOL(__xray_FunctionExit):
movl %r10d, %edi
movl $1, %esi
- ALIGNED_CALL_RAX
+ callq *%rax
.Ltmp2:
// Restore the important registers.
@@ -158,8 +167,10 @@ ASM_SYMBOL(__xray_FunctionExit):
movupd 16(%rsp), %xmm1
movq 8(%rsp), %rax
movq 0(%rsp), %rdx
- addq $56, %rsp
- CFI_DEF_CFA_OFFSET(8)
+ addq $64, %rsp
+ CFI_ADJUST_CFA_OFFSET(-64)
+
+ RESTORE_STACK_ALIGNMENT
retq
# LLVM-MCA-END
ASM_SIZE(__xray_FunctionExit)
@@ -174,6 +185,7 @@ ASM_SYMBOL(__xray_FunctionExit):
# LLVM-MCA-BEGIN __xray_FunctionTailExit
ASM_SYMBOL(__xray_FunctionTailExit):
CFI_STARTPROC
+ ALIGN_STACK_16B
SAVE_REGISTERS
movq ASM_SYMBOL(_ZN6__xray19XRayPatchedFunctionE)(%rip), %rax
@@ -182,11 +194,11 @@ ASM_SYMBOL(__xray_FunctionTailExit):
movl %r10d, %edi
movl $2, %esi
-
- ALIGNED_CALL_RAX
+ callq *%rax
.Ltmp4:
RESTORE_REGISTERS
+ RESTORE_STACK_ALIGNMENT
retq
# LLVM-MCA-END
ASM_SIZE(__xray_FunctionTailExit)
@@ -201,6 +213,7 @@ ASM_SYMBOL(__xray_FunctionTailExit):
# LLVM-MCA-BEGIN __xray_ArgLoggerEntry
ASM_SYMBOL(__xray_ArgLoggerEntry):
CFI_STARTPROC
+ ALIGN_STACK_16B
SAVE_REGISTERS
// Again, these function pointer loads must be atomic; MOV is fine.
@@ -223,10 +236,12 @@ ASM_SYMBOL(__xray_ArgLoggerEntry):
// 32-bit function ID becomes the first
movl %r10d, %edi
- ALIGNED_CALL_RAX
+
+ callq *%rax
.Larg1entryFail:
RESTORE_REGISTERS
+ RESTORE_STACK_ALIGNMENT
retq
# LLVM-MCA-END
ASM_SIZE(__xray_ArgLoggerEntry)
@@ -249,7 +264,7 @@ ASM_SYMBOL(__xray_CustomEvent):
testq %rax,%rax
je .LcustomEventCleanup
- ALIGNED_CALL_RAX
+ callq *%rax
.LcustomEventCleanup:
RESTORE_REGISTERS
@@ -275,7 +290,7 @@ ASM_SYMBOL(__xray_TypedEvent):
testq %rax,%rax
je .LtypedEventCleanup
- ALIGNED_CALL_RAX
+ callq *%rax
.LtypedEventCleanup:
RESTORE_REGISTERS
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