runtime: allow cgo callbacks on non-Go threads
Fixes #4435.
R=golang-dev, iant, alex.brainman, minux.ma, dvyukov
CC=golang-dev
https://golang.org/cl/7304104
diff --git a/src/pkg/runtime/asm_386.s b/src/pkg/runtime/asm_386.s
index 901d9f3..f09ddd0 100644
--- a/src/pkg/runtime/asm_386.s
+++ b/src/pkg/runtime/asm_386.s
@@ -476,21 +476,33 @@
// cgocallback(void (*fn)(void*), void *frame, uintptr framesize)
// See cgocall.c for more details.
TEXT runtime·cgocallback(SB),7,$12
- MOVL fn+0(FP), AX
- MOVL frame+4(FP), BX
- MOVL framesize+8(FP), DX
-
- // Save current m->g0->sched.sp on stack and then set it to SP.
+ // If m is nil, Go did not create the current thread.
+ // Call needm to obtain one for temporary use.
+ // In this case, we're running on the thread stack, so there's
+ // lots of space, but the linker doesn't know. Hide the call from
+ // the linker analysis by using an indirect call through AX.
+ get_tls(CX)
+#ifdef GOOS_windows
+ CMPL CX, $0
+ JNE 3(PC)
+ PUSHL $0
+ JMP needm
+#endif
+ MOVL m(CX), BP
+ PUSHL BP
+ CMPL BP, $0
+ JNE havem
+needm:
+ MOVL $runtime·needm(SB), AX
+ CALL AX
get_tls(CX)
MOVL m(CX), BP
- // If m is nil, it is almost certainly because we have been called
- // on a thread that Go did not create. We're going to crash as
- // soon as we try to use m; instead, try to print a nice error and exit.
- CMPL BP, $0
- JNE 2(PC)
- CALL runtime·badcallback(SB)
-
+havem:
+ // Now there's a valid m, and we're running on its m->g0.
+ // Save current m->g0->sched.sp on stack and then set it to SP.
+ // Save current sp in m->g0->sched.sp in preparation for
+ // switch back to m->curg stack.
MOVL m_g0(BP), SI
PUSHL (g_sched+gobuf_sp)(SI)
MOVL SP, (g_sched+gobuf_sp)(SI)
@@ -509,6 +521,10 @@
// a frame size of 12, the same amount that we use below),
// so that the traceback will seamlessly trace back into
// the earlier calls.
+ MOVL fn+0(FP), AX
+ MOVL frame+4(FP), BX
+ MOVL framesize+8(FP), DX
+
MOVL m_curg(BP), SI
MOVL SI, g(CX)
MOVL (g_sched+gobuf_sp)(SI), DI // prepare stack as DI
@@ -546,10 +562,38 @@
MOVL SI, g(CX)
MOVL (g_sched+gobuf_sp)(SI), SP
POPL (g_sched+gobuf_sp)(SI)
+
+ // If the m on entry was nil, we called needm above to borrow an m
+ // for the duration of the call. Since the call is over, return it with dropm.
+ POPL BP
+ CMPL BP, $0
+ JNE 3(PC)
+ MOVL $runtime·dropm(SB), AX
+ CALL AX
// Done!
RET
+// void setmg(M*, G*); set m and g. for use by needm.
+TEXT runtime·setmg(SB), 7, $0
+#ifdef GOOS_windows
+ MOVL mm+0(FP), AX
+ CMPL AX, $0
+ JNE settls
+ MOVL $0, 0x14(FS)
+ RET
+settls:
+ LEAL m_tls(AX), AX
+ MOVL AX, 0x14(FS)
+#endif
+ MOVL mm+0(FP), AX
+ get_tls(CX)
+ MOVL mm+0(FP), AX
+ MOVL AX, m(CX)
+ MOVL gg+4(FP), BX
+ MOVL BX, g(CX)
+ RET
+
// check that SP is in range [g->stackbase, g->stackguard)
TEXT runtime·stackcheck(SB), 7, $0
get_tls(CX)
