I am tring to write something like following in runtime package:
/usr/local/go/src/runtime/write_err_ios.go
```
// +build ios
// +build arm arm64
package runtime
import "unsafe"
var (
gWriteBuf [1024]byte
gWritePos int
)
//go:nosplit
func asmAslLogWrap(b unsafe.Pointer)
func writeErr(b []byte) {
// Write to stderr for command-line programs.
write(2, unsafe.Pointer(&b[0]), int32(len(b)))
for _, v := range b {
if v == 0 {
v = '0'
}
gWriteBuf[gWritePos] = v
gWritePos++
if v == '\n' || gWritePos == len(gWriteBuf)-1 {
gWriteBuf[gWritePos] = 0
asmAslLogWrap(unsafe.Pointer( &gWriteBuf[0] ))
gWritePos = 0
}
}
}
//go:cgo_import_static asl_log_wrap
```
/usr/local/go/src/runtime/write_err_ios_arm64.s
```
// +build ios,arm64
#include "funcdata.h"
#include "textflag.h"
TEXT runtime·asmAslLogWrap(SB),NOSPLIT,$0
MOVD b+0(FP), R0
B asl_log_wrap(SB)
```
```
// +build ios
package cgo
/*
#include <asl.h>
#include <stdlib.h>
void asl_log_wrap(const char *str) {
asl_log(NULL, NULL, ASL_LEVEL_NOTICE, "%s", str);
}
*/
import "C"
```
I can not write cgo in runtime package, The compiler failed with import
cycle.
I can not write cgo in runtime/cgo package and register a function pointer
in runtime package. It failed with a lot of runtime error "fatat error" msg
when painc was called.I think something enter a loop in systemstack() stuff.
Then I tried to write asm to call the c function directly,then I got :
```
runtime: unexpected return pc for runtime.notetsleepg called from
0xffffffffffffffff
fatal error: unknown caller pc
runtime stack:
runtime.throw(0x100d40317, 0x11)
/usr/local/go/src/runtime/panic.go:566 +0x80
runtime.gentraceback(0x1005a0704, 0x139523ef0, 0x0, 0x13957c9c0, 0x0, 0x0,
0x7fffffff, 0x16e84adb0, 0x0, 0x0, ...)
/usr/local/go/src/runtime/traceback.go:317 +0x147c
runtime.scanstack(0x13957c9c0, 0x13951b228)
/usr/local/go/src/runtime/mgcmark.go:783 +0x3c4
runtime.scang(0x13957c9c0, 0x13951b228)
/usr/local/go/src/runtime/proc.go:828 +0xd0
runtime.markroot.func1()
/usr/local/go/src/runtime/mgcmark.go:242 +0xc0
runtime.systemstack(0x13951b500)
/usr/local/go/src/runtime/asm_arm64.s:237 +0x90
runtime.mstart()
/usr/local/go/src/runtime/proc.go:1079
goroutine 26 [running]:
runtime.systemstack_switch()
/usr/local/go/src/runtime/asm_arm64.s:186 +0x8 fp=0x139525660 sp=0x139525650
runtime.markroot(0x13951b228, 0x10000000b)
/usr/local/go/src/runtime/mgcmark.go:247 +0x440 fp=0x1395256f0
sp=0x139525660
runtime.gcDrain(0x13951b228, 0x5)
/usr/local/go/src/runtime/mgcmark.go:969 +0x304 fp=0x139525740
sp=0x1395256f0
runtime.gcBgMarkWorker(0x13951a000)
/usr/local/go/src/runtime/mgc.go:1460 +0x624 fp=0x1395257b0 sp=0x139525740
runtime.goexit()
/usr/local/go/src/runtime/asm_arm64.s:983 +0x4 fp=0x1395257b0 sp=0x1395257b0
created by runtime.gcBgMarkStartWorkers
/usr/local/go/src/runtime/mgc.go:1349 +0x88
```
It looks like writeErr can be called successful a lot of times,but it will
crash when golang is doing some gc stuff.
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