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runtime: unexpected return pc for runtime.sigtramp on darwin/arm64 builder #29305

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eliasnaur opened this issue Dec 17, 2018 · 1 comment

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@eliasnaur
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commented Dec 17, 2018

From https://build.golang.org/log/93c24b649dcf7c5e192159c4ab4288094a7a0582:

...
##### GOMAXPROCS=2 runtime -cpu=1,2,4 -quick
lldb: running program
fatal error: unexpected signal during runtime execution
panic during panic
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x10067f0a4]

goroutine 0 [idle]:
runtime.throw(0x10090755a, 0x2a)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/runtime/panic.go:608 +0x4c fp=0x130011d10 sp=0x130011ce0 pc=0x10067ed64
runtime.sigpanic()
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/runtime/signal_unix.go:374 +0x43c fp=0x130011d40 sp=0x130011d10 pc=0x100693194
runtime.gcWriteBarrier(0x0, 0x100691eb4, 0x0, 0x130000000, 0x0, 0x100692b44, 0x3, 0x0, 0x0, 0x0, ...)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/runtime/asm_arm64.s:1165 +0x14 fp=0x130011e40 sp=0x130011d50 pc=0x1006ac9dc
runtime.startpanic_m(0x3)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/runtime/panic.go:747 +0x11c fp=0x130011e70 sp=0x130011e40 pc=0x10067f0a4
runtime.sighandler(0x100000003, 0x16f7aeac0, 0x16f7aeb28, 0x100b4e8a0)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/runtime/signal_sighandler.go:100 +0x510 fp=0x130011f20 sp=0x130011e70 pc=0x1006922c8
runtime.sigtrampgo(0x3, 0x16f7aeac0, 0x16f7aeb28)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/runtime/signal_unix.go:351 +0x1bc fp=0x130011fd0 sp=0x130011f20 pc=0x100692b44
runtime: unexpected return pc for runtime.sigtramp called from 0x0
stack: frame={sp:0x130011fd0, fp:0x130012060} stack=[0x130002000,0x130012000)
0000000130011ed0:  0000000000000000  0000000130000000 
0000000130011ee0:  0000000000000000  000000010088adc0 
0000000130011ef0:  000000010090c620  000000010088adc0 
0000000130011f00:  000000010090c620  000000016f7aeac0 
0000000130011f10:  000000016f7aeb28  0000000000000000 
0000000130011f20:  00000001006ad0dc <runtime.sigtramp+164>  0000000100000003 
0000000130011f30:  000000016f7aeac0  000000016f7aeb28 
0000000130011f40:  0000000100b4e8a0  0000000000000000 
0000000130011f50:  0000000000000000  0000000000000000 
0000000130011f60:  0000000000000000  0000000000000000 
0000000130011f70:  0000000000000000  0000000000000000 
0000000130011f80:  0000000100b4e8a0  0000000000000000 
0000000130011f90:  0000000000000000  0000000000000000 
0000000130011fa0:  0000000000000000  0000000000000000 
0000000130011fb0:  0000000000000000  0000000000000000 
0000000130011fc0:  0000000000000000  0000000000000000 
0000000130011fd0: <0000000000000000  0000000000000003 
0000000130011fe0:  000000016f7aeac0  000000016f7aeb28 
0000000130011ff0:  000000016f7aea10  0000000000000000 
runtime.sigtramp(0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/private/var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/go/src/runtime/sys_darwin_arm64.s:206 +0xa4 fp=0x130012060 sp=0x130011fd0 pc=0x1006ad0dc
...

I failed to find an open issue for the crash.

@ianlancetaylor

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commented Dec 17, 2018

I would guess that the "unexpected return PC" is because the traceback code is getting confused by the switch to the gsignal stack in runtime.sigtramp in runtime/sys_darwin_arm64.s.

But there is a deeper problem which is that we should not have called gcWriteBarrier, which is what led to the traceback crash. The signal handler code should have a valid G and M, but it need not have a valid P. The call to gcWriteBarrier is only OK if there is a valid P. Since sighandler calls startpanic_m, startpanic_m can't have any write barriers. But it does.

So this is an actual occurrence of #26575, which I think I previously deduced just by reading the code. Closing this issue as a dup.

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