[RFC] Introduce BreakAtCompileId

[Mikael Vidstedt]

> 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

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
>>> 
>