[xray] Preserve x8 in trampoline on AArch64

ianlevesque · ianlevesque · commit 4b9bef7e6cae · 2020-04-27T14:57:26.000-04:00
Summary: Fixes an ABI violation in the trampoline code for AArch64 that causes the indirect result register to get overwritten if the XRay handler function is complex enough to use it. Reviewers: MaskRay, dberris, johnislarry Subscribers: kristof.beyls, danielkiss, #sanitizers Tags: #sanitizers Differential Revision: https://reviews.llvm.org/D78596
diff --git a/compiler-rt/lib/xray/xray_trampoline_AArch64.S b/compiler-rt/lib/xray/xray_trampoline_AArch64.S
@@ -27,6 +27,10 @@ __xray_FunctionEntry:
     STP Q2, Q3, [SP, #-32]!
     STP Q4, Q5, [SP, #-32]!
     STP Q6, Q7, [SP, #-32]!
+    /* X8 is the indirect result register and needs to be preserved for the body
+     of the function to use */
+    STP X8, X0, [SP, #-16]!
+
     /* Load the page address of _ZN6__xray19XRayPatchedFunctionE into X1 */
     ADRP X1, _ZN6__xray19XRayPatchedFunctionE
     /* Load the handler function pointer into X2 */
@@ -41,6 +45,7 @@ __xray_FunctionEntry:
     BLR X2
 FunctionEntry_restore:
     /* Pop the saved registers */
+    LDP X8, X0, [SP], #16
     LDP Q6, Q7, [SP], #32
     LDP Q4, Q5, [SP], #32
     LDP Q2, Q3, [SP], #32
@@ -71,7 +76,14 @@ __xray_FunctionExit:
     STP X3, X4, [SP, #-16]!
     STP X5, X6, [SP, #-16]!
     STP X7, X30, [SP, #-16]!
-    STR Q0, [SP, #-16]!
+    STP Q0, Q1, [SP, #-32]!
+    STP Q2, Q3, [SP, #-32]!
+    STP Q4, Q5, [SP, #-32]!
+    STP Q6, Q7, [SP, #-32]!
+    /* X8 is the indirect result register and needs to be preserved for the body
+     of the function to use */
+    STP X8, X0, [SP, #-16]!
+
     /* Load the page address of _ZN6__xray19XRayPatchedFunctionE into X1 */
     ADRP X1, _ZN6__xray19XRayPatchedFunctionE
     /* Load the handler function pointer into X2 */
@@ -85,7 +97,11 @@ __xray_FunctionExit:
     /* Call the handler with 2 parameters in W0 and X1 */
     BLR X2
 FunctionExit_restore:
-    LDR Q0, [SP], #16
+    LDP X8, X0, [SP], #16
+    LDP Q6, Q7, [SP], #32
+    LDP Q4, Q5, [SP], #32
+    LDP Q2, Q3, [SP], #32
+    LDP Q0, Q1, [SP], #32
     LDP X7, X30, [SP], #16
     LDP X5, X6, [SP], #16
     LDP X3, X4, [SP], #16
