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SubjectRe: [PATCH 5/7] powerpc/ftrace: Update ftrace_location() for powerpc -mprofile-kernel
On Tue, 18 Jun 2019 23:53:11 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> Naveen N. Rao wrote:
> > Steven Rostedt wrote:
> >> On Tue, 18 Jun 2019 20:17:04 +0530
> >> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> >>
> >>> @@ -1551,7 +1551,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
> >>> key.flags = end; /* overload flags, as it is unsigned long */
> >>>
> >>> for (pg = ftrace_pages_start; pg; pg = pg->next) {
> >>> - if (end < pg->records[0].ip ||
> >>> + if (end <= pg->records[0].ip ||
> >>
> >> This breaks the algorithm. "end" is inclusive. That is, if you look for
> >> a single byte, where "start" and "end" are the same, and it happens to
> >> be the first ip on the pg page, it will be skipped, and not found.
> >
> > Thanks. It looks like I should be over-riding ftrace_location() instead.
> > I will update this patch.
>
> I think I will have ftrace own the two instruction range, regardless of
> whether the preceding instruction is a 'mflr r0' or not. This simplifies
> things and I don't see an issue with it as of now. I will do more
> testing to confirm.
>
> - Naveen
>
>
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -951,6 +951,16 @@ void arch_ftrace_update_code(int command)
> }
>
> #ifdef CONFIG_MPROFILE_KERNEL
> +/*
> + * We consider two instructions -- 'mflr r0', 'bl _mcount' -- to be part
> + * of ftrace. When checking for the first instruction, we want to include
> + * the next instruction in the range check.
> + */
> +unsigned long ftrace_location(unsigned long ip)
> +{
> + return ftrace_location_range(ip, ip + MCOUNT_INSN_SIZE);
> +}
> +
> /* Returns 1 if we patched in the mflr */
> static int __ftrace_make_call_prep(struct dyn_ftrace *rec)
> {
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 21d8e201ee80..122e2bb4a739 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1573,7 +1573,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
> * the function tracer. It checks the ftrace internal tables to
> * determine if the address belongs or not.
> */
> -unsigned long ftrace_location(unsigned long ip)
> +unsigned long __weak ftrace_location(unsigned long ip)
> {
> return ftrace_location_range(ip, ip);
> }

Actually, instead of making this a weak function, let's do this:


In include/ftrace.h:

#ifndef FTRACE_IP_EXTENSION
# define FTRACE_IP_EXTENSION 0
#endif


In arch/powerpc/include/asm/ftrace.h

#define FTRACE_IP_EXTENSION MCOUNT_INSN_SIZE


Then we can just have:

unsigned long ftrace_location(unsigned long ip)
{
return ftrace_location_range(ip, ip + FTRACE_IP_EXTENSION);
}

-- Steve

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