runtime: pass to signal handler value of g at time of signal
The existing code assumed that signals only arrived
while executing on the goroutine stack (g == m->curg),
not while executing on the scheduler stack (g == m->g0).
Most of the signal handling trampolines correctly saved
and restored g already, but the sighandler C code did not
have access to it.
Some rewriting of assembly to make the various
implementations as similar as possible.
Will need to change Windows too but I don't
understand how sigtramp gets called there.
R=r
CC=golang-dev
https://golang.org/cl/4203042
diff --git a/src/pkg/runtime/linux/arm/sys.s b/src/pkg/runtime/linux/arm/sys.s
index b25cf81..6c222fc 100644
--- a/src/pkg/runtime/linux/arm/sys.s
+++ b/src/pkg/runtime/linux/arm/sys.s
@@ -197,11 +197,24 @@
RET
TEXT runtime·sigtramp(SB),7,$24
+ // save g
+ MOVW g, R3
+ MOVW g, 20(R13)
+
+ // g = m->gsignal
MOVW m_gsignal(m), g
+
+ // copy arguments for call to sighandler
MOVW R0, 4(R13)
MOVW R1, 8(R13)
MOVW R2, 12(R13)
+ MOVW R3, 16(R13)
+
BL runtime·sighandler(SB)
+
+ // restore g
+ MOVW 20(R13), g
+
RET
TEXT runtime·rt_sigaction(SB),7,$0
