[CLOSED] SEGGER_RTT_vprintf / SEGGER_RTT_printf string format NULL check

ifmPhilipp · Dec 22nd 2022, 2:37pm

Hi Segger Team,

we're having software that passes printf format strings with %s in the format string, but the corresponding char * is NULL in same cases.

As it is cumbersome to check the variadic arguments (va_args) values before passing them into SEGGER_RTT_vprintf we do patch the Segger RTT sources with an additional check right now.

We also created a patch file: null_string_va_arg.zip

It would be nice, if this patch could get part of the official RTT release.

Thanks

Best regards
Philipp Häfele

mwb1100 · Dec 25th 2022, 9:34pm

If you make a patch to handle null strings, I suggest doing what gcc, msvc, and clang do: print "(null)" instead of printing nothing.

ifmPhilipp · Jan 10th 2023, 9:32am

Hi mwb1100,

wasn't aware of that behavior.

Patch would then look something like that:

Source Code: SEGGER_RTT_printf.c

if(s == NULL) {
_StoreChar(&BufferDesc, '(');
_StoreChar(&BufferDesc, 'n');
_StoreChar(&BufferDesc, 'u');
_StoreChar(&BufferDesc, 'l');
_StoreChar(&BufferDesc, 'l');
_StoreChar(&BufferDesc, ')');
break;
}

which is also totally ok :thumbup:

ifmPhilipp · Feb 3rd 2023, 11:03am

Hi,

there was an error in my code block i posted above, which i fixed there.

I now also created a patch file, including the "(null)" printing.

@SEGGER - Nino Any minds about this patch?

Best regards
Philipp

ifmPhilipp · Feb 3rd 2023, 1:15pm

Hi again,

i just found a much simpler and less error prone patch and also added a "NULL" fallback definition that i got from the SEGGER_RTT.c

null_string_va_arg_with_null_print_simplyfied.zip

Best regards
Philipp

SEGGER - Fabian · Apr 28th 2023, 5:17pm

Hi Philipp,
Sorry for the delay in response.

We agree that a crash should be avoided here.
We will add a "NULL" (or similar) return message at some point in the future.

Please note that we are currently fully booked with projects,
so we cannot provide a timeline for when this will be available.

We will close this thread now.

Best regards
Fabian

SEGGER - Fabian · Oct 16th 2023, 8:51am

Hi everyone,
this was officially added with the release of J-Link Software Version V7.92i.
Excerpt from the release notes:

Source Code

SEGGER_RTT_vprintf(): %s handling: In case string is NULL-pointer, function will now write "(NULL)" instead of doing a NULL-pointer access.

BR
Fabian Federschmidt

Source Code: SEGGER_RTT_printf.c

Source Code

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