Re: [PATCH 1/1] BaseTools/tools_def.template: revert to large code model for X64/GCC5/LTO

[Laszlo Ersek <lersek@redhat.com>]

On 08/22/17 16:15, Paolo Bonzini wrote:
> On 22/08/2017 16:03, Ard Biesheuvel wrote:
>> On 22 August 2017 at 14:27, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>> On 22/08/2017 13:59, Laszlo Ersek wrote:
>>>> This seems to suggest that "-pie" is the *master* switch (used only when
>>>> linking), and "-fpie" is a *prerequisite* for it (to be used both when
>>>> linking and compiling). Is this right?
>>>>
>>>> If so, then I think this is a gcc usability bug. We don't generally
>>>> start our thinking from the linker side. The above implies that the
>>>> simple (hosted) command line:
>>>>
>>>> $ gcc -o example -fpie source1.c source2.c
>>>>
>>>> could also result in miscompilation, because "-pie" is not given, only
>>>> "-fpie".
>>>
>>> No, GCC should add -pie on its own.
>>>
>>
>> I disagree. PIE linking and PIE code generation are two completely
>> different things.
> 
> What I'm saying is that GCC should add -pie on its own if you add -fpie
> to the linker command line.

Yes, that's my point, from a usability perspective.

While I hope to understand Ard's explanation (and it seems to confirm
that "-fpie" at compilation is a 'prerequisite' for "-pie" at linking),
again, this simply isn't how humans think about building binaries. If we
are required to call the compiler frontend for all purposes -- and we
seem to be required --, then we shouldn't have to express the same end
goal in different ways for different link-editing phases.

> But that would require changes to the
> compiler driver.
> 
> That said, the extra "-Wl," in "-Wl,-pie" is not necessary; the compiler
> driver knows "-pie" and swallows it when compiling (and passes it to the
> linker).

Now *that* I can get behind. If this works, then please let us do it --
replace "-fpie" with "-pie" in GCC44_X64_CC_FLAGS, and add no "-Wl,"
stuff to any DLINK defines.

Thanks!
Laszlo