Re: [PATCH v7 2/3] arm64: implement ftrace with regs

[Julien Thierry]

On 22/01/2019 13:28, Torsten Duwe wrote:
> On Tue, Jan 22, 2019 at 10:18:17AM +0000, Julien Thierry wrote:
>> Hi Torsten,
>>
>> A few suggestions below.
>>
>>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>>> +#define ARCH_SUPPORTS_FTRACE_OPS 1
>>> +#define REC_IP_BRANCH_OFFSET AARCH64_INSN_SIZE
>>> +/* All we need is some magic value. Simply use "_mCount:" */
>>
>> Nit: Should the casing be "_mcount" ?
> 
> No! The string makes it clear what it's supposed to be and the peculiar
> casing makes it unique and leaves no doubt were it came from. So whenever
> you see this register value in a crash dump you don't have to wonder about
> weird linkage errors, as it surely did not originate from a symtab.
> 

Right, I had missed the point that the value below is actually the
binary representation of that string. Things make more sense now, thanks.

>>> +#define MCOUNT_ADDR		(0x5f6d436f756e743a)
>>> +#else
>>> +#define REC_IP_BRANCH_OFFSET 0
>>> +#define MCOUNT_ADDR		((unsigned long)_mcount)
>>> +#endif
>>> +


-- 
Julien Thierry