Re: [PATCH] Compile elf/rtld.c with -fno-tree-loop-distribute-patterns.

[Florian Weimer <fw at deneb dot enyo dot de>]

* Sandra Loosemore:

>> Is it possible to do this via a pragma?  If I understand things
>> correctly, this is not necessary for PI_STATIC_AND_HIDDEN targets
>> (where initialization of the dynamic loader is simpler).
>
> I see that the definitions of memset and memmove use 
> "inhibit_loop_to_libcall" (which expands into an optimize attribute) to 
> prevent recursion, but I didn't think the header where that is defined 
> (include/libc-symbols.h) is supposed to be included in the dynamic 
> linker?

elf/rtld.os is built with -include ../include/libc-symbols.h, so the
declaration should be in scope.  I don't know why it is not effective.
It probably only applies to the implementations of memset and memmove
themselves (if the generic ones written in C are used).

>  Also, already in elf/Makefile there is another instance where 
> it adds -fno-tree-loop-distribute-patterns to the CFLAGS, so I just 
> copied that.  I don't work with glibc internals enough to have a good 
> feel for what the preferred solution is but I'll test a different 
> solution if this one isn't good enough.

I had hoped we could write something like this at the start of
elf/rtld.c:

#ifndef PI_STATIC_AND_HIDDEN
# pragma GCC optimize ("no-tree-loop-distribute-patterns")
#endif

Then the optimization would still be applied on the targets where it
is safe to do so.

But I don't have a strong opinion about this and would appreciate
feedback from others.