llvm dev - Nov 2019 - Debugging clang with debugger breakpoints ?

Hi All,

I want to understand some parts of ‘clang' by setting debug breakpoints. 

I have successfully done so with “llc” but I found that debugger breakpoints do
not work for ‘clang’

The apparent cause is that the clang code is run as a child process which is
created in the ‘Execute' function of ‘Program.inc'. The debugger stops
fine at breakpoints set on the main thread, but breakpoints do not work for any
code that is executed as the child process. I am compiling with Xcode in case
this makes a difference.

Thanks in advance for any help.

John

Run clang with -### to get the underlying command line (the one that has
the first argument "-cc1") and then run that command under the
debugger
instead.

On Mon, Nov 4, 2019 at 12:02 PM Joan Lluch via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi All,
>
> I want to understand some parts of ‘clang' by setting debug
breakpoints.
>
> I have successfully done so with “llc” but I found that debugger
> breakpoints do not work for ‘clang’
>
> The apparent cause is that the clang code is run as a child process which
> is created in the ‘Execute' function of ‘Program.inc'. The debugger
stops
> fine at breakpoints set on the main thread, but breakpoints do not work for
> any code that is executed as the child process. I am compiling with Xcode
> in case this makes a difference.
>
> Thanks in advance for any help.
>
> John
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hi David,

Thank you for your help. Please, can you elaborate on this?. The command line
that I get with -### starts with this:

clang version 9.0.1 (https://github.com/llvm/llvm-project.git
6e38ee067b8fa08792f551fb565bbb8ada4864b1)
Target: msp430
Thread model: posix
InstalledDir: /Users/joan/LLVM-9/llvm-project/build/Debug/bin
 "/Users/joan/LLVM-9/llvm-project/build/Debug/bin/clang"
"-cc1" "-triple" "msp430" "-emit-llvm"
"-disable-free" "-main-file-name" "main.c"
"-mrelocation-model" "static" "-mthread-model"
"posix" "-fmath-errno" "-masm-verbose"
"-mconstructor-aliases" "-nostdsysteminc"
"-dwarf-column-info" "-debugger-tuning=gdb"
"-target-linker-version" "305"
"-momit-leaf-frame-pointer" "-coverage-notes-file"
"/Users/joan/Documents-Local/Relay/RelayNou/main.gcno"
"-resource-dir"
"/Users/joan/LLVM-9/llvm-project/build/Debug/lib/clang/9.0.1"
"-internal-isystem"
"/Users/joan/LLVM-9/llvm-project/build/Debug/bin/../msp430/include"
"-Oz" "-fdebug-compilation-dir"
"/Users/joan/Documents-Local/Relay/RelayNou" "-ferror-limit"
"19" "-fmessage-length" "224"
"-fobjc-runtime=gcc" "-fdiagnostics-show-option"
"-fcolor-diagnostics" "-vectorize-slp" "-faddrsig"
"-o" "main.ll" "-x" "c"
"main.c"

So what should I set on the debugger?

Thanks

John





> On 4 Nov 2019, at 21:03, David Blaikie <dblaikie at gmail.com> wrote:
> 
> Run clang with -### to get the underlying command line (the one that has
the first argument "-cc1") and then run that command under the
debugger instead.
> 
> On Mon, Nov 4, 2019 at 12:02 PM Joan Lluch via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> Hi All,
> 
> I want to understand some parts of ‘clang' by setting debug
breakpoints.
> 
> I have successfully done so with “llc” but I found that debugger
breakpoints do not work for ‘clang’
> 
> The apparent cause is that the clang code is run as a child process which
is created in the ‘Execute' function of ‘Program.inc'. The debugger
stops fine at breakpoints set on the main thread, but breakpoints do not work
for any code that is executed as the child process. I am compiling with Xcode in
case this makes a difference.
> 
> Thanks in advance for any help.
> 
> John
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
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Joan Lluch via llvm-dev <llvm-dev at lists.llvm.org> writes:
> Hi All,
>
> I want to understand some parts of ‘clang' by setting debug
breakpoints.
>
> I have successfully done so with “llc” but I found that debugger
breakpoints do not work for ‘clang’
>
> The apparent cause is that the clang code is run as a child process
> which is created in the ‘Execute' function of ‘Program.inc'. The
> debugger stops fine at breakpoints set on the main thread, but
> breakpoints do not work for any code that is executed as the child
> process. I am compiling with Xcode in case this makes a difference.
David provided one answer but if your debugger supports it, an easier
way is to set the debugger to follow child processes.  With gdb it would
be "set follow-fork-mode child".

                 -David

Hi David,

I’m using the default Xcode debugger which happens to be Apple’s version of
LLDB. Is there something equivalent for it?.

Thanks

John

> On 8 Nov 2019, at 17:42, David Greene <greened at obbligato.org>
wrote:
> 
> Joan Lluch via llvm-dev <llvm-dev at lists.llvm.org> writes:
> 
>> Hi All,
>> 
>> I want to understand some parts of ‘clang' by setting debug
breakpoints.
>> 
>> I have successfully done so with “llc” but I found that debugger
breakpoints do not work for ‘clang’
>> 
>> The apparent cause is that the clang code is run as a child process
>> which is created in the ‘Execute' function of ‘Program.inc'.
The
>> debugger stops fine at breakpoints set on the main thread, but
>> breakpoints do not work for any code that is executed as the child
>> process. I am compiling with Xcode in case this makes a difference.
> 
> David provided one answer but if your debugger supports it, an easier
> way is to set the debugger to follow child processes.  With gdb it would
> be "set follow-fork-mode child".
> 
>                 -David