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SubjectRe: [PATCH 5/7] powerpc/ftrace: Update ftrace_location() for powerpc -mprofile-kernel
Steven Rostedt wrote:
> 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);
> }

Thanks, that's indeed nice. I hope you don't mind me adding your SOB for
that.

- Naveen


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