[XRay] Fix XRay PPC return value bug.

[timshen]

Summary

This bug is caused by the incorrect handling of return-value registers.

According to OpenPOWER 64-Bit ELF V2 ABI 2.2.5, up to 2 general-purpose
registers are going to be used for return values, and up to 8 floating
point registers or vector registers are going to be used for return
values.

[dberris]

LGTM

compiler-rt/lib/xray/xray_trampoline_powerpc64_asm.S

# floating point, and vector parameters, so that we only spill those live ones.
   addi 1, 1, 408
   ld 0, 16(1)
   blr
 
   .globl  __xray_FunctionExit
   .p2align  4
 __xray_FunctionExit:
   std 0, 16(1)
-  ld 0, -8(1) # FuncId
-  stdu 1, -72(1)
-# Spill r3, f1, and vsr34, the return value registers.
+  stdu 1, -256(1)
+# Spill r3-r4, f1-f8, and vsr34-vsr41, which are return registers.
+# If this appears to be slow, the caller needs to pass in number of generic,
+# floating point, and vector parameters, so that we only spill those live ones.
   std 3, 32(1)
-  mr 3, 0
-  addi 4, 1, 40
-  stxsdx 1, 0, 4
+  ld 3, 248(1) # FuncId
+  std 4, 40(1)
   addi 4, 1, 48
+  stxsdx 1, 0, 4
+  addi 4, 1, 56
+  stxsdx 2, 0, 4
+  addi 4, 1, 64
+  stxsdx 3, 0, 4
+  addi 4, 1, 72
+  stxsdx 4, 0, 4
+  addi 4, 1, 80
+  stxsdx 5, 0, 4
+  addi 4, 1, 88
+  stxsdx 6, 0, 4
+  addi 4, 1, 96
+  stxsdx 7, 0, 4
+  addi 4, 1, 104
+  stxsdx 8, 0, 4
+  addi 4, 1, 112
   stxvd2x 34, 0, 4
+  addi 4, 1, 128
+  stxvd2x 35, 0, 4
+  addi 4, 1, 144
+  stxvd2x 36, 0, 4
+  addi 4, 1, 160
+  stxvd2x 37, 0, 4
+  addi 4, 1, 176
+  stxvd2x 38, 0, 4
+  addi 4, 1, 192
+  stxvd2x 39, 0, 4
+  addi 4, 1, 208
+  stxvd2x 40, 0, 4
+  addi 4, 1, 224
+  stxvd2x 41, 0, 4
+  std 2, 240(1)
   mflr 0
-  std 0, 64(1)
+  std 0, 248(1)
+
   li 4, 1
   bl _ZN6__xray23CallXRayPatchedFunctionEi13XRayEntryType
   nop
-  ld 0, 64(1)
-  mtlr 0
-  ld 3, 32(1)
-  addi 4, 1, 40
-  lxsdx 1, 0, 4
+
   addi 4, 1, 48
+  lxsdx 1, 0, 4
+  addi 4, 1, 56
+  lxsdx 2, 0, 4
+  addi 4, 1, 64
+  lxsdx 3, 0, 4
+  addi 4, 1, 72
+  lxsdx 4, 0, 4
+  addi 4, 1, 80
+  lxsdx 5, 0, 4
+  addi 4, 1, 88
+  lxsdx 6, 0, 4
+  addi 4, 1, 96
+  lxsdx 7, 0, 4
+  addi 4, 1, 104
+  lxsdx 8, 0, 4
+  addi 4, 1, 112
   lxvd2x 34, 0, 4
-  addi 1, 1, 72
+  addi 4, 1, 128
+  lxvd2x 35, 0, 4
+  addi 4, 1, 144
+  lxvd2x 36, 0, 4
+  addi 4, 1, 160
+  lxvd2x 37, 0, 4
+  addi 4, 1, 176
+  lxvd2x 38, 0, 4
+  addi 4, 1, 192
+  lxvd2x 39, 0, 4
+  addi 4, 1, 208
+  lxvd2x 40, 0, 4
+  addi 4, 1, 224
+  lxvd2x 41, 0, 4
+  ld 0, 248(1)
+  mtlr 0
+  ld 2, 240(1)
+  ld 3, 32(1)
+  ld 4, 40(1)
+
+  addi 1, 1, 256
   ld 0, 16(1)
   blr

compiler-rt/test/xray/TestCases/Linux/coverage-sample.cc

 // Check that we can patch and unpatch specific function ids.
 //
 // RUN: %clangxx_xray -std=c++11 %s -o %t
 // RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false" %run %t | FileCheck %s
-// FIXME: When run this test case causes a segementation fault on powerpc64le.
-// Remove the xfail when the problem is fixed.
-// XFAIL: powerpc64le
 
 #include "xray/xray_interface.h"
 
 #include <set>
 #include <cstdio>
 
 std::set<int32_t> function_ids;