Re: libgo patch committed: Update to 1.7rc3

[Uros Bizjak <ubizjak at gmail dot com>]

On Thu, Aug 4, 2016 at 12:53 AM, Ian Lance Taylor <iant@golang.org> wrote:
> On Thu, Jul 28, 2016 at 4:24 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
>>
>> A new testsuite failure is introduced:
>>
>> FAIL: text/template
>>
>> on both, x86_64-linux-gnu and alpha-linux-gnu.
>>
>> The testcase corrupts stack with a too deep recursion.
>>
>> There is a part in libgo/go/text/template/exec.go that should handle
>> this situaiton:
>>
>> // maxExecDepth specifies the maximum stack depth of templates within
>> // templates. This limit is only practically reached by accidentally
>> // recursive template invocations. This limit allows us to return
>> // an error instead of triggering a stack overflow.
>> const maxExecDepth = 100000
>>
>> but the limit is either set too high, or the error handling code is
>> inefficient on both, split-stack (x86_64) and non-split-stack (alpha)
>> targets. Lowering this value to 10000 "fixes" the testcase on both
>> targets.
>
> I can not recreate this problem on x86 or x86_64.
>
> Does this patch work around the problem on Alpha?

Yes, the patch "fixes" the problem on alpha, but I still see the
failure on x86_64, even with the unlimited stack.

This is on Fedora 24, x86_64:

$ gmake -j 12 text/template/check
/home/uros/gcc-svn/trunk/libgo/testsuite/gotest: line 622:  4556
Segmentation fault      (core dumped) ./a.out -test.short
-test.timeout=${timeout}s "$@"
FAIL: text/template
Makefile:6285: recipe for target 'text/template/check' failed
gmake: *** [text/template/check] Error 1
$ ulimit -s
unlimited

Running the test under gdb:

(gdb) r
Starting program:
/ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x2aaaae93c700 (LWP 31972)]
[New Thread 0x2aaaaf740700 (LWP 31973)]
[New Thread 0x2aaaaf941700 (LWP 31974)]

Thread 1 "a.out" received signal SIGSEGV, Segmentation fault.
__generic_morestack (pframe_size=0x2aaaaff04170,
old_stack=0x2aaaaff04190, param_size=0) at
/home/uros/gcc-svn/trunk/libgcc/generic-morestack.c:573
573       current->old_stack = old_stack;
(gdb) c
Continuing.

Thread 1 "a.out" received signal SIGSEGV, Segmentation fault.
__generic_morestack (pframe_size=0x2aaaaff03aa0,
old_stack=0x2aaaaff03ac0, param_size=0) at
/home/uros/gcc-svn/trunk/libgcc/generic-morestack.c:573
573       current->old_stack = old_stack;
(gdb) c
Continuing.
[Thread 0x2aaaaf941700 (LWP 31974) exited]
[Thread 0x2aaaaf740700 (LWP 31973) exited]
[Thread 0x2aaaae93c700 (LWP 31972) exited]

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
(gdb)


Manually running the testcase:

[uros@localhost test]$ LD_LIBRARY_PATH=../../.libs ./a.out
fatal error: unexpected signal during runtime execution
[signal 0xb code=0x1 addr=0x47]

runtime stack:
runtime_dopanic
        /home/uros/gcc-svn/trunk/libgo/runtime/panic.c:135
runtime_throw
        /home/uros/gcc-svn/trunk/libgo/runtime/panic.c:193
sig_panic_leadin
        /home/uros/gcc-svn/trunk/libgo/runtime/go-signal.c:249
sig_panic_info_handler
        /home/uros/gcc-svn/trunk/libgo/runtime/go-signal.c:283

        :0
scanblock
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:1005
gc
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:2271
mgc
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:2215
runtime_mstart
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:1076

goroutine 392 [garbage collection]:
runtime_mcall
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:295
runtime_gc
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:2191
runtime_mallocgc
        /home/uros/gcc-svn/trunk/libgo/runtime/malloc.goc:259
text_template.walkTemplate.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:382
text_template.walk.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:239
text_template.walk.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:234
text_template.walkTemplate.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:383
text_template.walk.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:239
text_template.walk.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:234
text_template.walkTemplate.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:383
text_template.walk.pN19_text_template.state

[...]

        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:239
text_template.walk.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:234
text_template.walkTemplate.pN19_text_template.state
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/exec.go:383
created by testing.Run.pN9_testing.T
        /home/uros/gcc-svn/trunk/libgo/go/testing/testing.go:645

goroutine 16 [chan receive]:
runtime_mcall
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:295
chanrecv
        /home/uros/gcc-svn/trunk/libgo/runtime/chan.goc:269
testing.Run.pN9_testing.T
        /home/uros/gcc-svn/trunk/libgo/go/testing/testing.go:646
testing.$nested9
        /home/uros/gcc-svn/trunk/libgo/go/testing/testing.go:792
testing.tRunner
        /home/uros/gcc-svn/trunk/libgo/go/testing/testing.go:609
testing.RunTests
        /home/uros/gcc-svn/trunk/libgo/go/testing/testing.go:790
testing.Run.pN9_testing.M
        /home/uros/gcc-svn/trunk/libgo/go/testing/testing.go:742
main.main
        /ssd/uros/gcc-build/x86_64-pc-linux-gnu/libgo/gotest26048/test/_testmain.go:64
runtime_main
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:626
created by main
        /home/uros/gcc-svn/trunk/libgo/runtime/go-main.c:54

goroutine 17 [syscall]:
        goroutine in C code; stack unavailable
created by runtime_main
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:598

goroutine 18 [finalizer wait]:
runtime_mcall
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:295
runfinq
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:2512
kickoff
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:235
created by runtime_createfing
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:2577

goroutine 20 [runnable]:
runtime_mcall
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:295
bgsweep
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:1833
kickoff
        /home/uros/gcc-svn/trunk/libgo/runtime/proc.c:235
created by mgc
        /home/uros/gcc-svn/trunk/libgo/runtime/mgc0.c:2215

BTW: I can see this failure on other targets, too, e.g. powerpc64le
[1] and aarch64 [2].

[1] https://gcc.gnu.org/ml/gcc-testresults/2016-08/msg00321.html
[2] https://gcc.gnu.org/ml/gcc-testresults/2016-08/msg00318.html

Uros.