On 4/30/19 10:48 AM, Matthew Malcomson wrote: > Hi Jeff, > > On 30/04/19 16:29, Jeff Law wrote: >> On 1/4/19 9:03 AM, Matthew Malcomson wrote: >>> Hi there, >>> >>> I'm trying to figure out precisely what NOTE_INSN_FUNCTION_BEG means and >>> hoping someone here knows. >> It doesn't mean very much anymore. I believe it was used to >> distinguish between stuff like copying incoming arguments into pseudos >> and real user code. >> >> However, in a world with instruction scheduling and other code motion it >> just doesn't have much use because it's so imprecise, particularly as we >> get deeper into the RTL pipeline. >> > > Ah, I guess an imprecise marker probably needs an imprecise definition ;-) > >>> >> Well, the question I'd ask is precisely what are you trying to mark? > > > I'm wanting to mark the first instruction from "user code". > I'm trying to fix PR88432, where gdb puts the breakpoint from the > "start" command in the wrong place. > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88432 > > Gdb breaks on the second debug line entry in a function, which in > practice is the instruction directly after NOTE_INSN_FUNCTION_BEG. > > > The "fuzzy" definition from gccint.info didn't seem to explain what was > to happen with compiler inserted code that was not part of the prologue, > and this was what I was hoping to nail down. > > When looking, it seemed the note was being used in three slightly > different ways (I went into more information in the cover letter of my > [RFC] patch https://gcc.gnu.org/ml/gcc-patches/2019-01/msg00543.html ), > and I was hoping to get a precise definition so I could decide what > approach to take. ISTM that we should place the stack protector bits before the NOTE_INSN_FUNCTION_BEG. At least in the non-optimizing compile case that should make the right thing happen.
Jeff
