Comment 1:

Labels changed: added priority-later, removed priority-triage.

Status changed to Accepted.

Comment 2:

It's not a panic. If it's in non-Go code, it's a SIGSEGV.
There's very little we can do safely in this context.

Status changed to Unfortunate.

Comment 3:

From the description it looks like it talks about *Go* code in a callback on external
thread.

Comment 4:

right. it's about panic in Go callback functions, the following is a simpler reproducer:
// callback.go
package main
// void runThread(void);
import "C"
//export Callback
func Callback() {
    panic("callback panic")
}
func main() {
    C.runThread()
    select {}
}
// callback.c
#include <pthread.h>
#include "_cgo_export.h"
void *thread_main(void *unused) {
    Callback();
}
void runThread() {
    pthread_t p;
    pthread_create(&p, NULL, thread_main, NULL);
    pthread_join(p, 0);
}
Output:
$ ./test-panic 
SIGSEGV: segmentation violation
PC=0x1be6d

Comment 5:

Status changed to Accepted.

Comment 6:

g% ./callback
SIGSEGV: segmentation violation
PC=0x401c2dd
runtime.lessstack()
    /Users/rsc/g/go/src/pkg/runtime/asm_amd64.s:289 +0x1d
goroutine 3 [running]:
reflect.call(0x4059438, 0x421ef68)
    /Users/rsc/g/go/src/pkg/runtime/asm_amd64.s:235 fp=0x421ee58
runtime.panic(0x4021dc0, 0xc21000a010)
    /Users/rsc/g/go/src/pkg/runtime/panic.c:234 +0x51 fp=0x421ee98
main.Callback()
    /tmp/callback/x.go:9 +0x55 fp=0x421eec8
----- stack segment boundary -----
runtime.panic(0x4021dc0, 0xc21000a010)
    /Users/rsc/g/go/src/pkg/runtime/panic.c:247 +0x106 fp=0x421ee98
main.Callback()
    /tmp/callback/x.go:9 +0x55 fp=0x421eec8
----- stack segment boundary -----
runtime.cgocallbackg1()
    /Users/rsc/g/go/src/pkg/runtime/cgocall.c:311 +0xbf fp=0x421ef80
runtime.cgocallbackg()
    /Users/rsc/g/go/src/pkg/runtime/cgocall.c:281 +0x84 fp=0x421ef90
runtime.cgocallback_gofunc(0x0, 0x0, 0x0)
    /Users/rsc/g/go/src/pkg/runtime/asm_amd64.s:620 +0x67 fp=0x421efa0
runtime.goexit()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:1332 fp=0x421efa8
goroutine 1 [syscall]:
main._Cfunc_runThread(0x4010ed3)
    _/tmp/callback/_obj/_cgo_defun.c:43 +0x31
main.main()
    /tmp/callback/x.go:11 +0x1a
goroutine 4 [syscall]:
runtime.goexit()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:1332
rax     0xc2100016c0
rbx     0xc210012800
rcx     0x0
rdx     0x4059438
rdi     0xb0103e00
rsi     0xc210012840
rbp     0xc2100016c0
rsp     0x0
r8      0x421e000
r9      0x0
r10     0x21ec3fd6
r11     0x66a2222a
r12     0x2f83c0f0befae
r13     0x2fa72c37b97f0
r14     0x1315b87c3ec35a00
r15     0x4000f20
rip     0x401c2dd
rflags  0x10216
cs      0x2b
fs      0x0
gs      0x0
g%

Status changed to Fixed.