runtime: corruption in tests on freebsd-arm

[mknyszek]

#!watchflakes
default <- (`runtime.throw\(` || `^\s*fatal error:`) && builder == "freebsd-arm-paulzhol"

Broken out from #55167.

2023-06-07 02:51 freebsd-arm-paulzhol go@ea51e92c (log)

unexpected fault address 0x4d6149
fatal error: fault
[signal SIGBUS: bus error code=0x3 addr=0x4d6149 pc=0x1609c0]

goroutine 4945 [running]:
panic during panic
SIGBUS: bus error
PC=0x7cbd8 m=9 sigcode=3

/tmp/workdir-host-freebsd-arm-paulzhol/go/src/make.bash: line 226:  1079 Bus error               ./cmd/dist/dist bootstrap -a $vflag $GO_DISTFLAGS "$@"

[mknyszek]

CC @paulzhol

[paulzhol]

There was another one just now: https://build.golang.org/log/e2875c5b5673190c815f5401e660ca58ad44552c

Building packages and commands for freebsd/arm.
unexpected fault address 0x4d616f
fatal error: fault
[signal SIGBUS: bus error code=0x3 addr=0x4d616f pc=0x1613bc]

goroutine 4912 [running]:
panic during panic
SIGBUS: bus error
PC=0x7cffc m=8 sigcode=3

/tmp/workdir-host-freebsd-arm-paulzhol/go/src/make.bash: line 226:  1071 Bus error               ./cmd/dist/dist bootstrap -a $vflag $GO_DISTFLAGS "$@"

[paulzhol]

both addr=0x4d6149 and addr=0x4d616f are not aligned on a 4-byte boundary like one would expect on armv7.

[mknyszek]

Is it possible the compiler is emitting an unaligned load and other OSes for the architecture are masking it? Seems like we might need to reproduce this in gdb to get anything useful out of it.