runtime: AIX build broken with SIGSEGV

[ayappanec]

Go version

go version devel go1.24-a2a4f00783

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='ppc64'
GOBIN=''
GOCACHE='/home/buildusr/.cache/go-build'
GOENV='/home/buildusr/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='ppc64'
GOHOSTOS='aix'
GOINSECURE=''
GOMODCACHE='/home/buildusr/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='aix'
GOPATH='/home/buildusr/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/freeware/lib/golang'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/freeware/lib/golang/pkg/tool/aix_ppc64'
GOVCS=''
GOVERSION='go1.22.6'
GCCGO='gccgo'
GOPPC64='power8'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -maix64 -pthread -mcmodel=large -fmessage-length=0 -ffile-prefix-map=/tmp/go-build4155363056=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Trigger go build using make.bash

What did you see happen?

Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
# runtime
SIGSEGV: segmentation violation
PC=0x100075e74 m=8 sigcode=50 addr=0x20113f960

goroutine 0 gp=0xa00010000003500 m=8 mp=0xa00010000580008 [idle]:
runtime.getGCMaskOnDemand(0x100a0e960)
	runtime/type.go:108 +0x24 fp=0x110cd6570 sp=0x110cd6510 pc=0x100075e74
runtime.getGCMask(...)
	runtime/type.go:86
runtime.(*mspan).typePointersOfUnchecked(0xa00010000382cc0?, 0xa00010000382cc0?)
	runtime/mbitmap.go:200 +0x94 fp=0x110cd65b0 sp=0x110cd6570 pc=0x100012f84
runtime.scanobject(0xa00010000180000, 0xa0001000004c150)
	runtime/mgcmark.go:1426 +0x24c fp=0x110cd6648 sp=0x110cd65b0 pc=0x10002263c
runtime.gcDrain(0xa0001000004c150, 0x7)
	runtime/mgcmark.go:1228 +0x294 fp=0x110cd66c0 sp=0x110cd6648 pc=0x100021d24
runtime.gcDrainMarkWorkerIdle(...)
	runtime/mgcmark.go:1100
runtime.gcBgMarkWorker.func2()
	runtime/mgc.go:1519 +0x74 fp=0x110cd6720 sp=0x110cd66c0 pc=0x10001d614
runtime.systemstack(0x0)
	runtime/asm_ppc64x.s:256 +0x68 fp=0x110cd6740 sp=0x110cd6720 pc=0x100083038

goroutine 203 gp=0xa00010000923880 m=8 mp=0xa00010000580008 [GC worker (active)]:
runtime.systemstack_switch()
	runtime/asm_ppc64x.s:213 +0x10 fp=0xa000100005e3ee0 sp=0xa000100005e3ec0 pc=0x100082fb0
runtime.gcBgMarkWorker(0xa00010002c68380)
	runtime/mgc.go:1483 +0x270 fp=0xa000100005e3f98 sp=0xa000100005e3ee0 pc=0x10001d2f0
runtime.gcBgMarkStartWorkers.gowrap1()
	runtime/mgc.go:1339 +0x4c fp=0xa000100005e3fc0 sp=0xa000100005e3f98 pc=0x10001d06c
runtime.goexit({})
	runtime/asm_ppc64x.s:1022 +0x4 fp=0xa000100005e3fc0 sp=0xa000100005e3fc0 pc=0x100085a14
created by runtime.gcBgMarkStartWorkers in goroutine 1
	runtime/mgc.go:1339 +0x198

https://build.golang.org/log/3ddc19274de093367f9925b03a9135a64c5412e3

What did you expect to see?

The build break started after this change --> https://go-review.googlesource.com/c/go/+/616255

[gabyhelp]

Related Issues

• go1.22.8 runtime error: SIGSEGV: segmentation violation #70194 (closed)
• runtime: spurious SIGSEGV in systemstack() #68632
• runtime: SIGSEGV: segmentation violation #69247 (closed)
• cmd/dist: SIGSEGV during bootstrap on aix-ppc64 #58857 (closed)
• cmd/go: get in docker buildx gets SIGSEGV error #40969 (closed)
• x/sys/unix: mkerrors.sh broken on AIX #69365 (closed)
• runtime/traceback: segmentation violation failures from unwinding crash #64030
• SIGSEGV: segmentation violation code=0x1 - help #49992 (closed)
• cmd/compile/internal/ssa: SIGSEGV building 1.16 toolchain2 on openbsd/mips64 #44332 (closed)
• runtime: getArgInfo nil dereference #17471 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[ayappanec]

@randall77

[dmitshur]

CC @golang/aix.

[randall77]

It is failing when trying to do an atomic operation. The address looks strange, probably it isn't mapped.
I suspect what is happening is that aix/ppc64 doesn't do relocations from the rodata section to the data section correctly. (I think I remember something like that from long ago in my brain, not sure.)

If an aix and/or ppc64 person can confirm, I can think about how we might fix it. It may be tricky.

@golang/ppc64

[randall77]

My memory is of #58857

[randall77]

We might need to move all the types from SRODATA to SNOPTRDATA on aix.

[jkrishmys]

Hi @randall77, let me have a look and confirm. Thanks

[jkrishmys]

Hello @randall77, Here, during gc marking, r6 register holds 0x20114ac60, which is the faulting address. r3 and r7 both pointing to 0x100a0eb60
`# runtime [cmd/compile]
SIGSEGV: segmentation violation
PC=0x100075cf4 m=19 sigcode=50 addr=0x20114ac60.

goroutine 481 gp=0xa000100046c76c0 m=nil [GC worker (idle)]:
runtime.gopark(0x110166ee0?, 0x1?, 0x0?, 0x0?, 0xfffffffffffdfd2?)
/home/jkrishna/golang/golangdevel/goroot/src/runtime/proc.go:435 +0x144 fp=0xa000100046c8ee0 sp=0xa000100046c8eb0 pc=0x10007e054
runtime.gcBgMarkWorker(0xa00010003596620)
/home/jkrishna/golang/golangdevel/goroot/src/runtime/mgc.go:1423 +0x11c fp=0xa000100046c8f98 sp=0xa000100046c8ee0 pc=0x10001d11c
runtime.gcBgMarkStartWorkers.gowrap1()
/home/jkrishna/golang/golangdevel/goroot/src/runtime/mgc.go:1339 +0x4c fp=0xa000100046c8fc0 sp=0xa000100046c8f98 pc=0x10001cfec
runtime.goexit({})
/home/jkrishna/golang/golangdevel/goroot/src/runtime/asm_ppc64x.s:1022 +0x4 fp=0xa000100046c8fc0 sp=0xa000100046c8fc0 pc=0x100085874
created by runtime.gcBgMarkStartWorkers in goroutine 1
/home/jkrishna/golang/golangdevel/goroot/src/runtime/mgc.go:1339 +0x198

r0 0x0 r1 0x11151b510
r2 0x1100f8810 r3 0x100a0eb60
r4 0xa00010000300000 r5 0x10
r6 0x20114ac60 r7 0x100a0eb60
r8 0x1ea000 r9 0xa00010000300000
r10 0xa000100046d6818 r11 0x1101295e0
r12 0x100 r13 0x111523800
r14 0x1 r15 0x110129728
r16 0x6 r17 0xb9
r18 0xa0001000004cf08 r19 0xa0001000004e1a8
r20 0x20 r21 0x16
r22 0x11141be30 r23 0x11151b630
r24 0x0 r25 0x79afde02
r26 0xffffffffdca2bd19 r27 0xfffffffffa3cee9e
r28 0xfffffffffea0920e r29 0xa0001000004e198
r30 0xa000100006ae540 r31 0x100012f04
pc 0x100075cf4 ctr 0x9000000005e2700
link 0x100012f04 xer 0x20000000
ccr 0x42448228 trap 0x0
go tool dist: FAILED: /home/jkrishna/golang/golangdevel/goroot/pkg/tool/aix_ppc64/go_bootstrap install -a cmd/asm cmd/cgo cmd/compile cmd/link cmd/preprofile: exit status 1
` as in the previous issue #58857, there may be AIX relocation issue of rodata.

[randall77]

I poked at this and didn't make much progress. Without ssh access to a builder I can't really tell what is going on, or what fix might be productive. An AIX person needs to take the lead on this one.

Possible ideas:

1. Hack compiler to put types in the data section. I'm not sure this will work, as other things in rodata point to types (like itabs), so it's just pushing the problem elsewhere. But maybe we could find all the cases where this happens, or ...
2. Just get rid of rodata on aix, and just put everything that would have been in rodata into data (noptrdata?) instead.
3. Fix the aix loader so it handles rodata->data relocations correctly.

[jkrishmys]

Hello @randall77, thanks for the lead. We will work on it.

[jkrishmys]

I am playing with second idea of getting rid of rodata on AIX, and I am relatively new to golang linking. In symtab.go, I played with changing where the garbage collection symbols are collected, from rodata to noptr and data. Getting phase errors. Have changed the rodata sections to noptr in data.go file.
runtime.gcbss: phase error: addr=0x20085a35e but val=0x200859ea0 sym=runtime.gcbss type=SDATA sect=.data sect.addr=0x200859ea0 prev=runtime.gcdata