On Thu, Oct 31, 2019 at 09:02:32AM +0000, Mark Rutland wrote:
> On Wed, Oct 30, 2019 at 04:03:02PM +0100, Torsten Duwe wrote:
> > On Tue, Oct 29, 2019 at 04:58:26PM +0000, Mark Rutland wrote:
> > >
> > > I built parisc generic-{32,64}bit_defconfig with DYNAMIC_FTRACE enabled,
> > > and verified that the section made it into the .ko files for modules.
> >
> > This is because of remaining #ifdeffery in include/asm-generic/vmlinux.lds.h:
> >
> > #ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY
> > #define MCOUNT_REC() . = ALIGN(8); \
> > __start_mcount_loc = .; \
> > KEEP(*(__patchable_function_entries)) \
> > __stop_mcount_loc = .;
> > #else
> > #define MCOUNT_REC() . = ALIGN(8); \
> > __start_mcount_loc = .; \
> > KEEP(*(__mcount_loc)) \
> > __stop_mcount_loc = .;
> > #endif
>
> For modules we use a combination of scripts/module-common.lds and an
> architecture's own module.lds, not vmlinux.lds.h. So I don't think the above is
> relevant for modules.
Sure, this is only loosely related,...
> I agree that the CC_USING_PATCHABLE_FUNCTION_ENTRY ifdeffery could be
> simplified, and that it would be nice to consistently use
> FTRACE_CALLSITE_SECTION if we can. However, the generic linker script doesn't
> include anything, and I don't see a good location for that to live.
>
> What I could do is add an explicit comment:
>
> /*
> * The ftrace call sites are logged to a section whose name depends on the
> * compiler option used. A given kernel image will only use one, AKA
> * FTRACE_CALLSITE_SECTION. We capture all of them here to avoid header
> * dependencies.
> */
> #define MCOUNT_REC() \
> . = ALIGN(8); \
> __start_mcount_loc = .; \
> KEEP(*(__patchable_function_entries)) \
> KEEP(*(__mcount_loc)) \
> __stop_mcount_loc = .;
>
> ... which should make the dependency clear. Does that sound good to you?
Beautiful. I just didn't want to miss the opportunity to have this cleaned
up as well, and deemed this patch "closest" because of the definition of
FTRACE_CALLSITE_SECTION. Put it where you see it fit best.
Thanks,
Torsten
