runtime: use BX instead of R15 in race detector

If the race detector were runnable in dynamic linking mode,
then R15 would get clobbered. I don't think it is, so maybe
not a problem, but can't hurt to clean it up.

It also lets CL 283474 pass cleanly when checking the whole stdlib
(together with CL 288452).

Change-Id: I5a5021ecc7e7b8bed1cd3a7067c39b24c09e0783
Reviewed-on: https://go-review.googlesource.com/c/go/+/289270
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/runtime/race_amd64.s b/src/runtime/race_amd64.s
index c3b7bbfbfe2e8084780fa123c1b326252705a362..e10c21c7f363641b2daf79b356134c377b8f805d 100644 (file)
--- a/src/runtime/race_amd64.s
+++ b/src/runtime/race_amd64.s
@@ -184,7 +184,7 @@ TEXT        runtime·racefuncenter(SB), NOSPLIT, $0-8
 // Common code for racefuncenter/racefuncenterfp
 // R11 = caller's return address
 TEXT   racefuncenter<>(SB), NOSPLIT, $0-0
-       MOVQ    DX, R15         // save function entry context (for closures)
+       MOVQ    DX, BX          // save function entry context (for closures)
 #ifndef GOEXPERIMENT_REGABI
        get_tls(R12)
        MOVQ    g(R12), R14
@@ -193,9 +193,9 @@ TEXT        racefuncenter<>(SB), NOSPLIT, $0-0
        MOVQ    R11, RARG1
        // void __tsan_func_enter(ThreadState *thr, void *pc);
        MOVQ    $__tsan_func_enter(SB), AX
-       // racecall<> preserves R15
+       // racecall<> preserves BX
        CALL    racecall<>(SB)
-       MOVQ    R15, DX // restore function entry context
+       MOVQ    BX, DX  // restore function entry context
        RET
 
 // func runtime·racefuncexit()
@@ -376,7 +376,7 @@ racecallatomic_ignore:
        // Addr is outside the good range.
        // Call __tsan_go_ignore_sync_begin to ignore synchronization during the atomic op.
        // An attempt to synchronize on the address would cause crash.
-       MOVQ    AX, R15 // remember the original function
+       MOVQ    AX, BX  // remember the original function
        MOVQ    $__tsan_go_ignore_sync_begin(SB), AX
 #ifndef GOEXPERIMENT_REGABI
        get_tls(R12)
@@ -384,7 +384,7 @@ racecallatomic_ignore:
 #endif
        MOVQ    g_racectx(R14), RARG0   // goroutine context
        CALL    racecall<>(SB)
-       MOVQ    R15, AX // restore the original function
+       MOVQ    BX, AX  // restore the original function
        // Call the atomic function.
        MOVQ    g_racectx(R14), RARG0   // goroutine context
        MOVQ    8(SP), RARG1    // caller pc