Expanding and debugging macros

Expanding and debugging macros

[Jeffrey Walton]

Hi Everyone,

I'm trying to debug a c function that is mostly a massive collection of macros.

I changed the makefile recipe to preprocess the source trying to
produce something I can step:

#blake2b:    blake2b.c
#        $(CC) blake2b.c -o $@ $(CFLAGS) $(POWER8_CFLAG) -DBLAKE2B_SELFTEST

blake2b:    blake2b.c
        $(CC) -E blake2b.c -o blake2b.E $(CFLAGS) $(POWER8_CFLAG)
-DBLAKE2B_SELFTEST
        $(CC) -x c blake2b.E -o $@ $(CFLAGS) $(POWER8_CFLAG) -DBLAKE2B_SELFTEST

But GDB is not stepping it:

238      ROUND( 0 );
(gdb) s
239      ROUND( 1 );
(gdb) s
240      ROUND( 2 );
(gdb) q

I also switched to -save-temps with the same result - no stepping.

blake2b:    blake2b.c
        $(CC) -E blake2b.c -o blake2b.i $(CFLAGS) -save-temps
$(POWER8_CFLAG) -DBLAKE2B_SELFTEST
        $(CC) blake2b.i -o $@ $(CFLAGS) $(POWER8_CFLAG) -DBLAKE2B_SELFTEST

Is there a way to achieve this using GCC without changing the source files?

Thanks in advance.

Re: Expanding and debugging macros

[Alexander Monakov]

On Sat, 27 Jun 2020, Jeffrey Walton via Gcc-help wrote:

> Is there a way to achieve this using GCC without changing the source files?

Did you inspect the preprocessed file? It still has line directives pointing
to the original source. You'll need to remove them.

Alexander

Re: Expanding and debugging macros

[Edward Diener]

On 6/27/2020 7:23 AM, Jeffrey Walton via Gcc-help wrote:
> Hi Everyone,
>
> I'm trying to debug a c function that is mostly a massive collection 
> of macros.
>
> I changed the makefile recipe to preprocess the source trying to
> produce something I can step:
>
> #blake2b: blake2b.c
> # $(CC) blake2b.c -o $@ $(CFLAGS) $(POWER8_CFLAG) -DBLAKE2B_SELFTEST
>
> blake2b: blake2b.c
> $(CC) -E blake2b.c -o blake2b.E $(CFLAGS) $(POWER8_CFLAG)
> -DBLAKE2B_SELFTEST
> $(CC) -x c blake2b.E -o $@ $(CFLAGS) $(POWER8_CFLAG) -DBLAKE2B_SELFTEST
>
> But GDB is not stepping it:
>
> 238 ROUND( 0 );
> (gdb) s
> 239 ROUND( 1 );
> (gdb) s
> 240 ROUND( 2 );
> (gdb) q
>
> I also switched to -save-temps with the same result - no stepping.
>
> blake2b: blake2b.c
> $(CC) -E blake2b.c -o blake2b.i $(CFLAGS) -save-temps
> $(POWER8_CFLAG) -DBLAKE2B_SELFTEST
> $(CC) blake2b.i -o $@ $(CFLAGS) $(POWER8_CFLAG) -DBLAKE2B_SELFTEST
>
> Is there a way to achieve this using GCC without changing the source 
> files?
>
> Thanks in advance.
>

You can do step by step expansion of a macro using the Wave tool from 
the Wave library in Boost. It is excellent and works as a C++ standard 
compliant preprocessor. I have also found gcc's preprocessor to also be 
excellent and completely C++ standards compliant, so I would not be 
surprised if the step by step expansion if a macro using the Wave tool 
mimicked exactly the same step by step expansion of a macro in the gcc 
preprocessor.