Le 08/09/2022 à 15:48, Segher Boessenkool a écrit : > On Thu, Sep 08, 2022 at 06:00:24AM +0000, Christophe Leroy wrote: >> Looking at it more deeply, I see strange things. > > I'll have to see full generated machine code to be able to see strange > things, there isn't enough information at all here yet. Sorry.
Well, what I call strange is the fact that with GCC the number of bytes reported by -Wframe-larger-than doesn't match the value the offset used for the stwu at the start of the function, while it does with clang. > > Use private mail if it is too big or uninteresting for the list :-) > >> What is that frame size ? I thought it was the number of bytes r1 is >> decremented at the begining of the function, but it seems not, at least >> on GCC. It seems GCC substrats 112 bytes while clang doesn't. > > That is the vars size + the fixed size + the size of the parameter > save area + the size of the regs save area, rounded up to a multiple > of 16. Fixed size is 8 on 32-bit PowerPC ELF. Frame size used by GCC > here is just the vars size. Ok, so it means that the stack utilisation is underestimated when using GCC ? Or is it clang that overestimates it ? > >> So it seems that GCC and CLANG don't warn on the same thing, is that >> expected ? GCC substrats 112 bytes, which is the minimum frame size on a >> ppc64, but here I'm building a ppc32 kernel, min frame size is 16. > > I need to see the generated code to make sense of what is happening > here. It sounds like it is doing varargs calls or similar expensive > stack juggling. Or just saving a boatload of registers on the stack. > Ok, I'll send it to you. But once again, I don't mind what the code really look like, I'm just worried that GCC doesn't report the entire stack usage. Christophe
