On 26/02/16 23:54, Petr Mladek wrote:
> On Thu 2016-02-25 23:11:45, Balbir Singh wrote:
>> This applies on top of the patches posted by Michael today
>> Enable livepatching. This takes patch 6/8 and 7/8 of v8 as the base.
>> Removes the extra strict check in gcc-profile-kernel-notrace.sh
>> and adds logic for checking offsets in livepatch. The patch
>> for HAVE_C_RECORDMCOUNT is not required and not used here.
>>
>> Depending on whether or not a TOC is generated, the offset
>> for _mcount can be +16 or +8. The changes are such that the
>> offset checks are specific to powerpc.
>>
>> Comments? Testing? I tested the sample in the livepatch
>> directory
>>
>> --- /dev/null
>> +++ b/arch/powerpc/include/asm/livepatch.h
>> +#define ARCH_HAVE_KLP_MATCHADDR
>> +static inline int klp_matchaddr(struct ftrace_ops *ops, unsigned long ip,
>> + int remove, int reset)
>> +{
>> + int offsets[] = {8, 16};
>> + int i;
>> + int ret = 1;
>> +
>> + for (i = 0; i < ARRAY_SIZE(offsets); i++) {
>> + ret = ftrace_set_filter_ip(ops, ip+offsets[i], remove, reset);
> The serach for the right address might get replaced by
> ftrace_location call.
>
> But instead of blindly trying to get the right address. I would
> suggest to implement a function that will search the ftrace
> location for the given function address. I means something like:
>
> /**
> * function_to_ftrace_location - get ftrace location for the given
> * function address.
> * @addr: function address
> *
> * Returns the address of the ftrace location for the given function.
> * Returns 0 if the address does not correspond to any function
> * or if the function can not be traced.
> */
> unsigned long function_to_ftrace_location(unsigned long addr)
> {
> const struct dyn_ftrace *rec;
> const struct ftrace_page *pg;
> unsigned long symbol_size, offset, post_addr;
> unsigned long ret = 0UL;
>
> if (!kallsyms_lookup_size_offset(addr, &symbol_size, &offset))
> return 0UL;
>
> addr -= offset;
> post_addr = addr += symbol_size;
>
> mutex_lock(&ftrace_lock);
> do_for_each_ftrace_rec(pg, rec) {
> if (rec->ip >= addr && rec->ip < post_addr ) {
> ret = rec->ip;
> goto end;
> }
> } while_for_each_ftrace_rec()
I thought of this as well, I was thinking of modifying ftrace_location(), but that would be a larger change
> end:
> mutex_unlock(&ftrace_lock);
>
> return ret;
> }
>
> The function is just compile tested on x86_64. We had similar function
> in the SUSE-specific LivePatch implementation before we realized
> that only fentry (zero offset) could be reasonable supported
> on x86_64.
>
> I will prepare a proper patch/patches for PPC early next week.
> I have attended a training this week and am snowed under mails
> a bit.
>
Sounds good!
Balbir Singh
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