[RFC] Introduce BreakAtCompileId

[Leslie Zhai]

在 2020年11月10日 12:45, Mikael Vidstedt 写道:
>
>> On Nov 9, 2020, at 5:31 PM, Leslie Zhai <zhaixiang at loongson.cn> wrote:
>>
>> Hi Mikael,
>>
>> Thanks for your teaching!
>>
>>
>> 在 2020年11月10日 06:24, Mikael Vidstedt 写道:
>>> Please take this to hotspot-dev-compiler if you want to continue the discussion.
>>>
>>>
>>> FWIW “continue” does take an argument, would that work for your use case?
>> Yes!  It should work for my use case.  It doesn't need to make the same wheel any more :)
>>
>>> (gdb) help continue
>>> Continue program being debugged, after signal or breakpoint.
>>> Usage: continue [N]
>>> If proceeding from breakpoint, a number N may be used as an argument,
>>> which means to set the ignore count of that breakpoint to N - 1 (so that
>>> the breakpoint won't break until the Nth time it is reached).
>> NullCheck  also generated signal SIGSEGV:
>>
>>
>>      064       LD    Rd, [Rt + #12 (8-bit)]  @ indOffset8    # compressed ptr @ loadN ! Field: java/lang/String.value
>>      068       decode_heap_oop   Rd, Rt  @ decodeHeapOop
>>      070       MOV    Rd, [Rt + #12 (8-bit)]  @ indOffset8 @ loadRange
>> =>074       NullCheck   Rd
>>
>>
>> It needs to press `c` when the base register is indeed NULL by comparing with other CPUs.  So continue N -1 might not precise.
> Indeed. You may or may not be interested in another gdb command: handle SIGSEGV nostop noprint

But some NullCheck should not be NULL.  So it couldn't echo `handle 
SIGSEGV nostop noprint` >> ~/.gdbinit

I fixed a NullCheck related bug for C2 compiler this morning :)

Cheers,
Leslie Zhai

>
> There are of course pros and cons to ignoring that and other signals like it.
>
> Cheers,
> Mikael
>
>> Thanks,
>> Leslie Zhai
>>
>>> If non-stop mode is enabled, continue only the current thread,
>>> otherwise all the threads in the program are continued.  To
>>> continue all stopped threads in non-stop mode, use the -a option.
>>> Specifying -a and an ignore count simultaneously is an error.
>>>
>>>
>>> Cheers,
>>> Mikael
>>>
>>>
>>>> On Nov 9, 2020, at 7:48 AM, Leslie Zhai <zhaixiang at loongson.cn> wrote:
>>>>
>>>> Hi,
>>>>
>>>> OptoBreakpoint is very useful for debugging C2 compiler when porting some cpu for jdk8u. It is able to `b breakpoint` for breaking at the prolog about for example Compile_id = 2. But when fixed several bugs for C2, it needs to press `c` times and times again for reaching the proper Compile_id.
>>>>
>>>> I `grep` Opto related options.  But there is no such one to break at the precise Compile_id.  Please teach me if there was :)
>>>>
>>>> So here comes BreakAtCompileId. It is able to break at the precise Compile_id which you want to debug.
>>>>
>>>>
>>>> gdb -ex=r --args $JAVA -Xcomp -XX:+PrintCompilation -XX:BreakAtCompileId=430  -version
>>>>
>>>>
>>>> (gdb) b breakpoint
>>>> Breakpoint 1 at 0x7ffff633b0d0: breakpoint. (133 locations)
>>>>
>>>>     6333  433       3 java.util.ImmutableCollections$List12::get (35 bytes)   made not entrant
>>>>
>>>> Thread 2 "java" hit Breakpoint 1, 0x00007ffff711f410 in os::breakpoint() () at /home/zhaixiang/projects
>>>> 452         if (pslash != NULL) {
>>>> (gdb) si
>>>> 0x00007fffe01b46d1 in ?? ()
>>>> (gdb) x/22i $pc-44
>>>>     0x7fffe01b46a5:      shl    $0x3,%edx
>>>>     0x7fffe01b46a8:      movabs $0x800000000,%r11
>>>>     0x7fffe01b46b2:      add    %r11,%r10
>>>>     0x7fffe01b46b5:      cmp    %r10,%rax
>>>>     0x7fffe01b46b8:      jne    0x7fffd87cf920
>>>>     0x7fffe01b46be:      nop
>>>>     0x7fffe01b46bf:      nop
>>>>     0x7fffe01b46c0:      mov    %eax,-0x16000(%rsp)
>>>>     0x7fffe01b46c7:      push   %rbp
>>>>     0x7fffe01b46c8:      sub    $0x10,%rsp
>>>>     0x7fffe01b46cc:      callq  0x7ffff711f410 <_ZN2os10breakpointEv>
>>>> => 0x7fffe01b46d1:      mov    0xc(%rsi),%r11d
>>>>     0x7fffe01b46d5:      mov    0x10(%rsi),%r10d
>>>>     0x7fffe01b46d9:      cmp    %r11d,%r10d
>>>>     0x7fffe01b46dc:      je     0x7fffe01b46f6
>>>>     0x7fffe01b46de:      mov    $0x1,%eax
>>>>     0x7fffe01b46e3:      add    $0x10,%rsp
>>>>     0x7fffe01b46e7:      pop    %rbp
>>>>     0x7fffe01b46e8:      cmp    0x128(%r15),%rsp
>>>>     0x7fffe01b46ef:      ja     0x7fffe01b46fa
>>>>     0x7fffe01b46f5:      retq
>>>>     0x7fffe01b46f6:      xor    %eax,%eax
>>>> (gdb) i r
>>>> rax            0x7fffe01b46c0      140736953272000
>>>> rbx            0x8004699e8         34364365288
>>>> rcx            0x1                 1
>>>> rdx            0x7fffc5068980      140736498928000
>>>> rsi            0x62a020b40         26474580800
>>>> rdi            0x1                 1
>>>> rbp            0x7ffff5a668d0      0x7ffff5a668d0
>>>> rsp            0x7ffff5a66290      0x7ffff5a66290
>>>> r8             0x80008eeb0         34360323760
>>>> r9             0x7ffb4cf60         34354810720
>>>> r10            0x800012488         34359813256
>>>> r11            0x800000000         34359738368
>>>> r12            0x0                 0
>>>> r13            0x7292dae5          1922226917
>>>> r14            0x62a020818         26474579992
>>>> r15            0x7ffff00271e0      140737220080096
>>>> rip            0x7fffe01b46d1      0x7fffe01b46d1
>>>> eflags         0x206               [ PF IF ]
>>>> cs             0x33                51
>>>> ss             0x2b                43
>>>> ds             0x0                 0
>>>> es             0x0                 0
>>>> fs             0x0                 0
>>>> gs             0x0                 0
>>>>
>>>>
>>>> Thanks,
>>>> Leslie Zhai
>>>>