[XRay][compiler-rt] Stash flags as well in x86_64 trampoline

Summary:
This change saves and restores the full flags register in x86_64 mode.
This makes running instrumented signal handlers safer, and avoids flags
set during the execution of the event handlers from polluting the
instrumented call's flags state.

Reviewers: kpw, eizan, jfb

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D51277

llvm-svn: 340812

diff --git a/compiler-rt/lib/xray/xray_trampoline_x86_64.S b/compiler-rt/lib/xray/xray_trampoline_x86_64.S
index 99ad396..9dffae0 100644 (file)
--- a/compiler-rt/lib/xray/xray_trampoline_x86_64.S
+++ b/compiler-rt/lib/xray/xray_trampoline_x86_64.S
@@ -19,6 +19,7 @@
 
 
 .macro SAVE_REGISTERS
+       pushfq
        subq $240, %rsp
        CFI_DEF_CFA_OFFSET(248)
        movq %rbp, 232(%rsp)
@@ -69,6 +70,7 @@
        movq  8(%rsp), %r14
        movq  0(%rsp), %r15
        addq    $240, %rsp
+       popfq
        CFI_DEF_CFA_OFFSET(8)
 .endm