[XRay][x86_64] Define a tail exit trampoline.

Summary:
We define a new trampoline that's a hybrid between the exit and entry
trampolines with the following properties:

- Saves all of the callee-saved registers according to the x86_64
  calling conventions.
- Indicate to the log handler function being called that this is a
  function exit event.

This fixes a bug that is a result of not saving enough of the register
states, and that the log handler is clobbering registers that would be
used by the function being tail-exited into manifesting as runtime
errors.

Reviewers: rSerge, echristo, majnemer

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D26020

llvm-svn: 285787

1 files changed, 1 insertions, 0 deletions

diff --git a/compiler-rt/lib/xray/xray_interface_internal.h b/compiler-rt/lib/xray/xray_interface_internal.h
index 24a5acc97a5..c4f72433d17 100644
--- a/compiler-rt/lib/xray/xray_interface_internal.h
+++ b/compiler-rt/lib/xray/xray_interface_internal.h
@@ -61,6 +61,7 @@ extern "C" {
 // basis. See xray_trampoline_*.S files for implementations.
 extern void __xray_FunctionEntry();
 extern void __xray_FunctionExit();
+extern void __xray_FunctionTailExit();
 }
 
 #endif