perf probe: register type casting to string

[Milian Wolff <milian.wolff@kdab.com>]

Hey all,

it seems like it's impossible to use the :string type cast feature of perf 
probe when using a register as the source. I.e.:

~~~~~
┌milian@agathebauer:/tmp
└$ cat test.c
void blub(const char* l)
{
}

int main(int argc, char** argv)
{
  blub(argv[0]);
  return 0;
}
┌milian@agathebauer:/tmp
└$ gcc -O0 -g test.c
┌milian@agathebauer:/tmp
└$ perf probe -x ./a.out 'blub label=%di:string'
Failed to write event: Invalid argument
  Error: Failed to add events.
~~~~~~

Is there anything I'm missing? When I use `l` instead of `%di` it works. But 
if I'm trying to add a tracepoint to a library that got stripped and is 
missing debug symbols, what can I do?

Thanks
-- 
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts