Ingo Molnar wrote:
let me qualify that: parameters must be prepared there too - but no
actual function call inserted. (at most a NOP inserted). The register
filling doesnt even have to be function-calling-convention compliant -
that makes the symbolic probe almost zero-impact to register
allocation/scheduling, the only thing it should ensure is that the
parameters that are annotated to be available in register, stack or
memory _somewhere_. (i.e. not hidden or destroyed at that point by gcc)
Does a simple asm() that takes read-only parameters but only adds a NOP
achieve this result?
Do you mean using the asm to make sure gcc puts a reference to a
variable into the DWARF info, or some other way of encoding the value
locations?
Hm, another problem. If the mark is in a loop, and gcc decides to
unroll the loop, then you'll probably only get a mark in one iteration
of the loop (or 1/Nth of the iterations). Or worse, assembler errors.
The only way I can see to deal with this is to not use symbols, but put
records in a special section. That way, if the asm() inserting them
gets duplicated, you'll get duplicate records in the marker section.
I guess you'd get a similar problem with markers inserted in inlined
functions.
(How does gdb deal with breakpoints in unrolled loops?)
J
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