On Tue, Jan 23, 2018 at 11:38 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
> On Tue, Jan 23, 2018 at 8:32 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
>> On Tue, Jan 23, 2018 at 5:49 AM, Ian Lance Taylor <i...@golang.org> wrote:
>>> On Sun, Jan 21, 2018 at 3:13 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
>>>>
>>>> The default "go build" compile options over-optimize the auxiliary
>>>> executable, built in TestCrashDumpsAllThreads testcase
>>>> (libgo/go/runtime/crash_unix_test.go). This over-optimization results
>>>> in removal of the trivial summing loop and in the inlining of the
>>>> main.loop function into main.$thunk0.
>>>>
>>>> The testcase expects backtrace that shows several instances of
>>>> main.loop in the backtrace dump. When main.loop gets inlined into
>>>> thunk, its name is not dumped anymore.
>>>>
>>>> The solution is to pass "-O0" to gccgo, which inhibits unwanted inlining.
>>>>
>>>> Patch was bootstrapped and regression tested on x86_64-linux-gnu and
>>>> alphev68-linux-gnu, where for the later target the patch fixed the
>>>> mentioned failure.
>>>
>>> That sounds like a bug somewhere. Even when one function gets inlined
>>> into another, its name should still be dumped. This is implemented by
>>> report_inlined_functions in libbacktrace/dwarf.c. While something
>>> like your patch may be needed, I'd like to more clearly understand why
>>> libbacktrace isn't working.
>>
>> If I manually compile the testcase from crash_unix_test.go wth gccgo
>> -O2 (the asm is attached), the main.loop function is not even present
>> in the dump.
>
> Digging deeper into the source, here is the problem:
[...]
> So, those $LBB labels are at the wrong place. During runtime, we get
> (oh, why can't we display PC in hex?!):
Following testcase:
--cut here--
package main
func loop(i int, c chan bool) {
close(c)
for {
for j := 0; j < 0x7fffffff; j++ {
}
}
}
--cut here--
can be compiled with a crosscompiler to alpha-linux-gnu:
~/gcc-build-alpha/gcc/go1 -O2 -fkeep-static-functions l.go
to generate assembly, where $LBB2 is placed after "lda" insn.
main.loop:
...
$L2:
lda $1,-1($1)
$LBB2:
$LM6:
bne $1,$L2
br $31,$L3
$LBE2:
...
and in ._final, we can see that (note 52) is in wrong place. It should
be placed in front of (insn 13).
(code_label 14 6 12 2 (nil) [1 uses])
(note 12 14 13 [bb 4] NOTE_INSN_BASIC_BLOCK)
(insn:TI 13 12 52 (set (reg:DI 1 $1 [orig:70 ivtmp_1 ] [70])
(plus:DI (reg:DI 1 $1 [orig:70 ivtmp_1 ] [70])
(const_int -1 [0xffffffffffffffff]))) 7 {*adddi_internal}
(nil))
(note 52 13 15 0x7f6b5f2791e0 NOTE_INSN_BLOCK_BEG)
(jump_insn:TI 15 52 45 (set (pc)
(if_then_else (ne (reg:DI 1 $1 [orig:70 ivtmp_1 ] [70])
(const_int 0 [0]))
(label_ref:DI 14)
(pc))) "l.go":6 169 {*bcc_normal}
(int_list:REG_BR_PROB 1062895956 (nil))
-> 14)
(note 45 15 46 [bb 5] NOTE_INSN_BASIC_BLOCK)
(jump_insn:TI 46 45 47 (set (pc)
(label_ref 16)) 200 {jump}
(nil)
-> 16)
(barrier 47 46 32)
(note 32 47 54 NOTE_INSN_DELETED)
(note 54 32 0 0x7f6b5f2791e0 NOTE_INSN_BLOCK_END)
I will open a PR:
Uros.
