[llvm-dev] How does -fPIE get passed from clang to llc when run on a .ll file?

[Eric Christopher via llvm-dev]

We should probably make this a nomerge IR option.

On Fri, Nov 6, 2015, 11:24 AM Akira Hatanaka via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> If the target platform is linux and -fPIE is on the command line, clang
> sets TargetOptions::PositionIndependentExecutable in
> EmitAssemblyHelper::CreateTargetrMachine.
>
>
> On Fri, Nov 6, 2015 at 11:20 AM, Phil Tomson via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>>
>>
>> On Fri, Nov 6, 2015 at 11:10 AM, Tim Northover <t.p.northover at gmail.com>
>> wrote:
>>
>>> On 6 November 2015 at 11:00, Phil Tomson <phil.a.tomson at gmail.com>
>>> wrote:
>>> > With 3.6 I get an unused argument warning with -enable-pie:
>>> >
>>> > $ clang -v -emit-llvm -enable-pie -O0 -S global_dat.c -o
>>> > global_dat_x86_pie.ll
>>>
>>> Yes, it's an llc option not a Clang option. It actually looks like
>>> Clang doesn't forward it to LLVM at all (almost certainly a bug, if
>>> so). But that's probably OK because the only place LLVM actually uses
>>> it at all is to determine what kind of TLS model to use
>>> (TargetMachine.cpp), which linkers can mostly relax anyway.
>>>
>>
>> In my case I'm actually working on a backend for a new architecture and
>> need this to show up in LLVM because certain pseudo ops need to be expanded
>> in a certain way if we're using PIE (vs. just a default static link). So
>> are these options accessible in the Target-specific code?
>>
>>>
>>> It does seem to get passed onto the linker by Clang though.
>>>
>>
>> Not sure how that can work.
>>
>>
>>> Cheers.
>>>
>>> Tim.
>>>
>>
>>
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>>
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