Messages in this thread | | | Subject | Re: [PATCH 1/3] powerpc, Makefile: Make it possible to safely select CONFIG_FRAME_POINTER | From | Steven Rostedt <> | Date | Sat, 02 May 2009 22:04:09 -0400 |
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On Sat, 2009-05-02 at 21:48 +0200, Segher Boessenkool wrote: > > This patch introduces HAVE_NORMAL_FRAME_POINTER Kconfig symbol. When > > defined, the top level Makefile won't add -fno-omit-frame-pointer > > cflag (the flag is useless for PowerPC kernels, and also makes gcc > > generate wrong code). > > > +++ b/arch/powerpc/Kconfig > > > + select HAVE_NORMAL_FRAME_POINTER > > > +config HAVE_NORMAL_FRAME_POINTER > > + bool > > + help > > + Architectures should select this symbol if their ABI implies > > + having a frame pointer. > > I am totally confused what you call a frame pointer here. > None of the relevant PowerPC ABIs have a frame pointer > separate from the stack pointer; the compiler can create > one, of course. A better config symbol name and help text > would help understand this patch :-)
Yeah, I agree. This needs a better description. I only know what's going on because I was there for the start of the discussion.
But just to be sure, this is what I think is happening.
When we add "-pg" to gcc, it automatically causes frame pointers to be used.
But with PPC, it always has frame pointers and there's no problem.
But with Linux, when you add CONFIG_FRAME_POINTER, it automatically adds: -fno-omit-frame-pointer. Thus the config will add "-fomit-frame-pointer" when CONFIG_FRAME_POINTER is not set, or it will add "-fno-omit-frame-pointer" when it is set.
The problem with PPC is that "-fno-omit-frame-pointer" is buggy and causes gcc to produce bad code.
Perhaps a better name would be:
HAVE_FRAME_POINTER_AS_DEFAULT
??
Or am I totally wrong in my analysis?
-- Steve
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