Re: [RFC Patch, Aarch64] : Macros for profile code generation to enable gprof support

[Marcus Shawcroft <marcus dot shawcroft at arm dot com>]

On 03/08/13 19:01, Venkataramanan Kumar wrote:


> 2013-08-02  Venkataramanan Kumar  <venkataramanan.kumar@linaro.org>
>
>           * config/aarch64/aarch64.h (MCOUNT_NAME): Define.
>             (NO_PROFILE_COUNTERS): Likewise.
>             (PROFILE_HOOK): Likewise.
>             (FUNCTION_PROFILER): Likewise.
>          *  config/aarch64/aarch64.c (aarch64_function_profiler): Remove.
>             .
>
> regards,
> Venkat.

Hi Venkat,

Looking at the various other ports it looks that the majority choose to 
use FUNCTION_PROFILER_HOOK rather than PROFILE_HOOK.

Using PROFILE_HOOK to inject a regular call to to _mcount() means that 
all arguments passed in registers in every function will be spilled and 
reloaded because the _mcount call will kill the caller save registers.

Using the FUNCTION_PROFILER_HOOK and taking care not to kill the caller 
save registers would be less invasive.  The LR argument to _mcount would 
need to be passed in a temporary register, say x9 and _mcount would also 
need to ensure caller save registers are saved and restored.

The latter seems to be a better option to me, is there compelling reason 
to choose PROFILE_HOOK over FUNCTION_PROFILER_HOOK ??

Cheers
/Marcus