runtime: arm softfloat segfaults after rev ceb13960d05

[davecheney]

What steps will reproduce the problem?

CL 75320043 causes nilptr2.go to segfault on arm5.

What is the expected output? What do you see instead?

# ../test
# go run run.go -- nilptr2.go
incorrect output
SIGSEGV: segmentation violation
PC=0x2df10

goroutine 16 [running]:
stepflt(0x11444, 0xb6ed8edc)
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/src/pkg/runtime/softfloat_arm.c:569 +0x1bb8 fp=0xb6ed8ec0
runtime._sfloat2(0x11444, 0x0, 0xb6ed8100, 0xb6ed8f28, 0x10224000, ...)
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/src/pkg/runtime/softfloat_arm.c:610 +0x18 fp=0xb6ed8ed4
_sfloat()
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/src/pkg/runtime/vlop_arm.s:78 +0x34 fp=0xb6ed8f18
main.func·019()
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/test/nilptr2.go:64 +0x2c fp=0xb6ed8f24
main.func·054()
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/test/nilptr2.go:19 +0xa4 fp=0xb6ed8f40
main.main()
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/test/nilptr2.go:20 +0x118 fp=0xb6ed8f90
runtime.main()
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/src/pkg/runtime/proc.c:243 +0xf8 fp=0xb6ed8fc4
runtime.goexit()
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/src/pkg/runtime/proc.c:1446 fp=0xb6ed8fc4
created by _rt0_go
    /export/builder/workspace/linux-arm-arm5-ceb13960d05b/go/src/pkg/runtime/asm_arm.s:72 +0xb0

Please use labels and text to provide additional information.

http://build.golang.org/log/0a6c5a851f055c6f971b365ab3438d44ad3fef3e

[dvyukov]

Comment 1:

This a latent bug in arm softfloat. It panics with runtime locks held.
The test is very lucky that it was succeeding at all. It will break badly in any real
program.
The easiest fix is to detect signal in softfloat code and undo the lock (m->locks--)
before panicing.

[rsc]

Comment 2:

Owner changed to @rsc.

Status changed to Started.

[rsc]

Comment 3:

This issue was closed by revision b2cbf49.

Status changed to Fixed.