[RFC 1/8] trace: correct handling of recursive call

[Heinrich Schuchardt]

On 12/27/25 14:45, Simon Glass wrote:
> Hi Heinrich,
> 
> On Sat, 20 Dec 2025 at 18:59, Heinrich Schuchardt
> <heinrich.schuchardt at canonical.com> wrote:
>>
>> __cyg_profile_func_enter() adds timer information to function traces.
>>
>> Commit 852d4dbd70ba ("trace: Detect an infinite loop") introduced a logic
>> letting any recursive call to __cyg_profile_func_enter() deactivate
>> tracing.
>>
>> This implies that a lot of the DM core and timer drivers functions need to
>> be marked as `notrace`. This in not desirable as those functions are part
>> of what we want to trace when not invoked by __cyg_profile_func_enter().
>>
>> A better approach than switching of tracing is to immediately leave
>> __cyg_profile_func_enter() when reentered.
>>
>> Reported-by: Patrick Rudolph <patrick.rudolph at 9elements.com>
>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
>> ---
>>   lib/trace.c | 59 ++++++++++++++++++++++++-----------------------------
>>   1 file changed, 27 insertions(+), 32 deletions(-)
>>
> 
> Please see here:
> 
> https://docs.u-boot.org/en/latest/develop/trace.html#board-requirements
> 
> This really just papers over the problem you are having. You cannot
> use driver model to obtain the timer as tracing starts before that.
> 
> So please instead do the small extra work of defining timer_get_us()
> for your board.

Hello Simon,

Thank you for reviewing the series.

Making timer_get_us() driver model independent could alleviate the 
issues that I tried to address with patch 2/8 (trace: initr_trace must 
succeed initr_dm). Yet, the current patch is about handling recursive calls.

I think we should use notrace only on the minimum set of functions that 
are used by tracing only. All functions that may also be used from 
outside of the tracing framework should be instrumented.

This patch addresses how to avoid recursion when instrumented functions 
are called by the instrumentation entry and exit functions. This should 
be handled gracefully instead marking it as a total failure and 
disabling the tracing framework.

Best regards

Heinrich