[forking for different topics] "Maciej W. Rozycki" <ma...@codesourcery.com> writes: > On Sat, 4 Feb 2012, Richard Sandiford wrote: >> > I don't think _mcount has ever worked for dynamic libraries, has it? -- >> > please correct me if I am wrong, but I believe `gprof' relies on memory >> > segments to be contiguous which is certainly not the case for a dynamic >> > executable where you have a separate set of mappings for the executable >> > proper and then for each shared library loaded. >> > >> > I didn't know it required $3 for anything either -- I've thought it was >> > $1 only. How has it worked for standard MIPS code then? >> >> Sorry, I misremembered, it was $2 (for the static chain register). > > Please elaborate anyway -- if you remember the details of $2 usage > offhand, that is. I'm curious.
$2 was the traditional static chain pointer, and _mcount would preserve it so that calls from nested functions would work correctly. We since changed GCC's own static pointer to $15, so we now have to move $15 to $2 before calling _mcount and restore it afterwards, since there's no guarantee that _mcount itself will preserve $15. Or at least, that's the theory. I have to admit to never using it in "real world" situations. Richard
