Re: [PATCH 5/5] Add single-threaded path to _int_malloc

[Szabolcs Nagy <szabolcs dot nagy at arm dot com>]

On 24/10/17 14:49, Wilco Dijkstra wrote:
> DJ Delorie wrote:
>>
>> Looks good to me.
> 
> OK it's all committed now. Thanks for the reviews!
> 
>>> We could use the ifunc mechanism to decide between different variants - 
>>> including for example for the single-thread optimization.
>>
>> I suspect ifuncs are chosen before we know if the program will spawn any
>> threads, though.
> 
> I was thinking of dynamically updating the ifunc, for example if we want to trace,
> hook or enable more expensive checking. That way there is no need to check
> for all special cases on every call, and additional code can be enabled or
> disabled at runtime by swapping to a different variant of malloc/free.
> 

the address of malloc must be const during the lifetime of a
process, since it can be saved in a variable that can be later
used as func ptr.

you would need an additional indirection for this to work.
(e.g. implement it as void *malloc(size_t n){ return fptr(n); }
where fptr is a global that's updated at thread creation time)
at which point it has not much to do with ifunc.