[lldb-dev] Stopping "stop reason = exec"

[Jim Ingham via lldb-dev]

Yup, apparently debugserver tells us the stop is for exec directly so we don't treat it as a breakpoint hit.  That sorta makes sense, you don't want to trigger a breakpoint hit every time you find a thread at the pc of a breakpoint (might be a thread that hit a breakpoint, then didn't get to run till the next stop.)  But it defeats the obvious method.

Anyway, it is a program stop, so you can use a stop hook:

(lldb) target stop-hook add -n _dyld_start -o continue

That one does work, though the stop-hook output is a little ugly.  It would also be nice to specify stop-hooks by stop reason too.  But this method does work...

Jim


> On Dec 4, 2017, at 4:36 PM, Chris Lattner <sabre at nondot.org> wrote:
> 
>> On Dec 4, 2017, at 4:25 PM, Chris Lattner <sabre at nondot.org> wrote:
>>> For macOS, you can also just do:
>>> 
>>> (lldb) break set -n _dyld_start --skip-prologue 0 -s dyld
>>> Breakpoint 2: where = dyld`_dyld_start, address = 0x000000010000b19c
>>> (lldb) b com add -o continue
>>> either in your .lldbinit or in your debug session.  
>> 
>> This doesn’t appear to work, I tried both lldb and in a debug session.  I’m starting lldb with “lldb -- swiftc … “ if that matters.
>> 
>> (lldb) break set -n _dyld_start --skip-prologue 0 -s dyld
>> Breakpoint 1: where = dyld`_dyld_start, address = 0x0000000000001000
>> (lldb) b com add -o continue
>> Breakpoint 2: no locations (pending).
>> WARNING:  Unable to resolve breakpoint to any actual locations.
> 
> I realize that this is probably because you’re not using the standard ‘b’ alias.  When I use ‘br’, the command succeeds, but I still stop on launch:
> 
> (lldb) br com add -o continue
> (lldb) r
> There is a running process, kill it and restart?: [Y/n] y
> Process 24049 exited with status = 9 (0x00000009) 
> Process 24054 launched: '/Users/clattner/Projects/build/Xcode-ReleaseAssert+swift-DebugAssert/swift-macosx-x86_64/Debug/bin/swiftc' (x86_64)
> Process 24054 stopped
> * thread #2, stop reason = exec
>     frame #0: 0x0000000109852000 dyld`_dyld_start
> dyld`_dyld_start:
> ->  0x109852000 <+0>: popq   %rdi
>     0x109852001 <+1>: pushq  $0x0
>     0x109852003 <+3>: movq   %rsp, %rbp
>     0x109852006 <+6>: andq   $-0x10, %rsp
> Target 0: (swiftc) stopped.
> 
> 
> Thank you for the help, I appreciate it!
> 
> -Chris
>