go: runtime: mysterious bit set of a high order bit causes segfaults and bounds check failures

#!watchflakes
post <- goarch == "ppc64" && ((log ~ `SIGSEGV` && log ~ `0x0x8000`) || (log ~ `runtime error: index out of range`))

New segfault found in the gopls tests.

2023-11-20 18:35 linux-ppc64-sid-buildlet tools@8966034e go@ddb38c3f x/tools/gopls/internal/regtest/marker (log)

SIGSEGV: segmentation violation
PC=0x28e6c m=9 sigcode=3 addr=0x800000000b53940

goroutine 0 gp=0xc00070fa00 m=9 mp=0xc000744008 [idle]:
runtime.(*mspan).typePointersOfUnchecked(0xc00b8b0000?, 0xc00b959d70?)
	/workdir/go/src/runtime/mbitmap_allocheaders.go:202 +0x4c fp=0xc000fade38 sp=0xc000faddf8 pc=0x28e6c
runtime.scanobject(0xc00b8b0000, 0xc00004fc48)
	/workdir/go/src/runtime/mgcmark.go:1446 +0xcc fp=0xc000faded0 sp=0xc000fade38 pc=0x360fc
runtime.gcDrainN(0xc00004fc48, 0x10000)
	/workdir/go/src/runtime/mgcmark.go:1331 +0x1f0 fp=0xc000fadf10 sp=0xc000faded0 pc=0x35e30
...
r18  0xc00004ea08	r19  0xc000050a30
r20  0xa8	r21  0xc000744008
r22  0xc000faa3a0	r23  0xc000fadeb8
r24  0x5a	r25  0xf0
r26  0xc0129eaa1b	r27  0xc0129eaa17
r28  0x0	r29  0xc000050a28
r30  0xc00070fa00	r31  0x360fc
pc   0x28e6c	ctr  0x7fff9bdf04d0
link 0x360fc	xer  0x20000000
ccr  0x44428084	trap 0x380

— watchflakes

_Originally posted by @gopherbot in https://github.com/golang/go/issues/63736#issuecomment-1819714566_

About this issue

Original URL
State: closed
Created 7 months ago
Comments: 20 (19 by maintainers)

Most upvoted comments

That is easy, fortunately. All 5 instances are running on a resource restricted container within the same VM.

pmur on Nov 30, 2023

If this is a generic ppc64 bug, I’d expect to see sporadic failures on the openbsd and aix builders. Both compile GOPPC64=power8 (but run on P9).

pmur on Nov 30, 2023

You are definitely not incorrect.

randall77 on Nov 30, 2023

I’d err on the side of bogus. I think mapped memory usually falls below 0x8000000000000000 on PPC64 in most cases. ppc64/linux doesn’t support PIC, so all static data/text should occupy fairly low addresses starting at 0x10000.

pmur on Nov 20, 2023