runtime: some cgo tests are failing on freebsd/arm64

[dmgk]

There still seem to be some issues with cgo, see https://golang.org/cl/199919:

--- FAIL: TestSigStackSwapping (12.99s)
    crash_test.go:95: testprogcgo SigStack exit status: signal: segmentation fault (core dumped)
    crash_cgo_test.go:480: expected "OK\n" got 
--- FAIL: TestCgoNumGoroutine (12.93s)
    crash_test.go:95: testprogcgo NumGoroutine exit status: signal: segmentation fault (core dumped)
    crash_cgo_test.go:411: expected "OK\n" got 
--- FAIL: TestEnsureDropM (21.49s)
    crash_test.go:95: testprogcgo EnsureDropM exit status: signal: segmentation fault (core dumped)
    crash_cgo_test.go:174: expected "OK\n", got 
--- FAIL: TestCgoExternalThreadSignal (26.27s)
    crash_cgo_test.go:129: exit status: signal: segmentation fault (core dumped)
--- FAIL: TestCgoExternalThreadPanic (11.53s)
    crash_test.go:95: testprogcgo CgoExternalThreadPanic exit status: signal: segmentation fault (core dumped)
    crash_cgo_test.go:82: want failure containing "panic: BOOM". output:
        
--- FAIL: TestCgoExternalThreadSIGPROF (26.92s)
    crash_cgo_test.go:106: exit status: signal: segmentation fault (core dumped)
--- FAIL: TestCgoCallbackGC (12.73s)
    crash_test.go:95: testprogcgo CgoCallbackGC exit status: signal: segmentation fault (core dumped)
    crash_cgo_test.go:70: expected "OK\n", but got:
FAIL
FAIL	runtime	101.212s
FAIL

Not sure whether these are the same as the cgo issues @dmgk and @MikaelUrankar saw. Or maybe these are some changes I forgot to pick up during rebase of https://golang.org/cl/198544.

Originally posted by @tklauser in #24715 (comment)

[gopherbot]

Change https://golang.org/cl/203519 mentions this issue: cmd/link: switch to ld.bfd on freebsd/arm64

[dmgk]

This appears to be is an issue with LLD 8.0.1 (FreeBSD 366581-1200008) on FreeBSD aarch64.

Stacktrace from failing NumGoroutine test in src/runtime/testdata/testprogcgo:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000000000033ded8 in runtime.adjustSignalStack (sig=<optimized out>, mp=0x0, gsigStack=0xffffbf7f98c8, ~r3=<optimized out>)
    at /home/builder/goroot/src/runtime/signal_unix.go:374
374             if sp >= mp.gsignal.stack.lo && sp < mp.gsignal.stack.hi {
[Current thread is 1 (LWP 101003)]
Breakpoint 1 at 0x3568fc: file /home/builder/goroot/src/runtime/tls_arm64.s, line 13.
Breakpoint 2 at 0x3558d8: file /home/builder/goroot/src/runtime/asm_arm64.s, line 995.
Loading Go Runtime support.
(gdb) bt
#0  0x000000000033ded8 in runtime.adjustSignalStack (sig=<optimized out>, mp=0x0, gsigStack=0xffffbf7f98c8, ~r3=<optimized out>)
    at /home/builder/goroot/src/runtime/signal_unix.go:374
#1  0x000000000033ddf0 in runtime.sigtrampgo (sig=11, info=0xffffbf7f99e0, ctx=0xffffbf7f9a30)
    at /home/builder/goroot/src/runtime/signal_unix.go:347
#2  0x0000000000356650 in runtime.sigtramp () at /home/builder/goroot/src/runtime/sys_freebsd_arm64.s:323
#3  <signal handler called>
#4  runtime.cgocallback_gofunc () at /home/builder/goroot/src/runtime/asm_arm64.s:1039
#5  0x00000000003558b0 in runtime.cgocallback () at /home/builder/goroot/src/runtime/asm_arm64.s:983
#6  0x00000000003ae538 in _cgoexp_690828bc0c24_CallbackNumGoroutine (a=0xffffbf7f9f87, n=0, ctxt=0) at _cgo_gotypes.go:432
#7  0x0000000000397adc in crosscall2 () at /home/builder/goroot/src/runtime/cgo/asm_arm64.s:47
#8  0x0000000000000000 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

I (sort of) narrowed the issue down to https://github.com/golang/go/blob/master/src/runtime/tls_arm64.s#L11 - when linked with ld.lld, g gets loaded with a wrong value.

/cc @MikaelUrankar @tklauser

[gopherbot]

Change https://golang.org/cl/199919 mentions this issue: cmd/nm, runtime/cgo: add cgo support for freebsd/arm64

[tklauser]

Seems to be fixed by https://golang.org/cl/203519