[PATCH] D92633: Add -f[no-]direct-access-external-data to deprecate -mpie-copy-relocations

[Sriraman Tallam via Phabricator via cfe-commits]

tmsriram added a comment.

In D92633#2433979 <https://reviews.llvm.org/D92633#2433979>, @MaskRay wrote:

> In D92633#2433108 <https://reviews.llvm.org/D92633#2433108>, @tmsriram wrote:
>
>> You said : "The name -mpie-copy-relocations is misleading [1] and does not capture the idea that this option can actually apply to all of -fno-pic,-fpie, ..."
>>
>> Could you please clarify why this option needs to apply to -fno-pic?  Here is what I tried with trunk clang:
>
> If the user wants to guarantee no copy relocations in -fno-pic code, they can theoretically apply -fno-direct-access-external-data to use a GOT indirection.
> This is not implemented, though.
>
>> extern int var;
>> int get() { return var; }
>>
>> $ clang -S foo.c -o -
>> ....
>> 	movl	var, %eax
>> 	popq	%rbp
>> ...
>>
>> With -fno-pic,  this will never need to use -mpie-copy-relocations at all, so this case is not relevant right?  Did I miss anything?
>
> -fno-pic code can only be used with -no-pie links (position-dependent executables) If var is not defined in the linked executable, it will have a copy relocation.

Thanks for explaining.  I know that by default (i.e. no-pic and no-pie), copy relocations will be used for external data accesses.  So, you are saying that you are adding a mechanism to disable copy relocations for the no-pic/no-pie case too. Is there a need for this, purely a question.  I know that copy relocations are frowned upon so maybe there was a feature request. If so, citing that would make it more clear. Thanks.


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