[cfe-dev] Should -nostdlib control runtime libraries?

[Petr Hosek via cfe-dev]

On Tue, Jun 25, 2019 at 12:12 AM Eric Fiselier <eric at efcs.ca> wrote:

> Does `-nodefaultlibs` drop the library?
>

The only difference between -nostdlib and -nodefaultlibs is whether you get
start files or not (i.e. crt1.o, crtbegin.o, crtend.o, crtn.o).


> Within libc++, it's been quite useful to assume -fsanitize=foo opts you
> into the required libraries despite passing `-nostdlib`
> (It only does this on some platforms). Because, at the moment, correctly
> re-building the compiler-rt link line is all but impossible.
>

It sounds like a dedicated flag might be preferable to have a more
flexibility.


> Whatever decision we make, let's make it consistent across platforms?
>

I completely agree with that.


> /Eric
>
>
> On Sun, Jun 23, 2019 at 8:50 PM Petr Hosek via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> We're trying to enable profile instrumentation in our kernel. We would
>> like to use -fprofile-instr-generate to enable the instrumentation,
>> but provide our own runtime instead of the one that's part of
>> compiler-rt which isn't compatible with the kernel environment.
>> However, there's no way to tell the driver to avoid linking the
>> runtime. This is the case not only for profile runtime, but for other
>> runtimes like XRay or sanitizers as well.
>>
>> -nostdlib already controls whether system libraries are being linked
>> into binary. Furthermore, when compiler-rt builtins are being used, it
>> also controls whether those are being linked as well. This is somewhat
>> inconsistent with other compiler runtimes mentioned above.
>>
>> Two potential solutions I came up with are:
>>
>> 1. Change -nostdlib to affect linking of runtime libraries. This would
>> make it consistent with the behavior it has when using compiler-rt
>> builtins. However, it would also make it inconsistent with GCC, e.g.
>> when you use --coverage -nostdlib, GCC would still pass -lgcov to the
>> linker.
>>
>> 2. Introduce a new flag, e.g. -nortlib, that would control linking of
>> runtime libraries, including compiler-rt builtins.
>>
>> Do you have any opinion on this or any other suggestions?
>> _______________________________________________
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>> cfe-dev at lists.llvm.org
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>>
>
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