mstorsjo added inline comments.
================
Comment at: lib/Frontend/InitPreprocessor.cpp:684
+ else if (TI.getTriple().isThumb() || TI.getTriple().isARM())
+ Builder.defineMacro("__ARM_DWARF_EH__");
+ }
----------------
martell wrote:
> mstorsjo wrote:
> > Won't this start setting this define also on platforms where ARM EHABI is
> > the default? (I.e. all ELF platforms except netbsd)?
> It will set it on any arm / thumb platform where exceptions are enabled and
> the current model is dwarf.
> This includes netbsd. The issue we have is that apple set this
> unconditionally for their watch platform.
>
> I'm wondering if we should put this behind a `!apple` guard or just add an
> `if windows or netbsd` guard.
>
> Or is it okay to just generally have this macro on all platforms where dwarf
> is exception model and the target is arm?
>
No, it will set it on any arm/thumb platform where one hasn't indicated
preference for any other model. And there are more models than just
dwarf/seh/sjlj - there's also the ARM EHABI model. (According to
MC/MCTargetOptions.h in llvm, there aren't any more than this currently though.)
Prior to this patch, `clang -x c++ -target armv7-linux-gnueabihf -E -dM - <
/dev/null` will not include `__ARM_DWARF_EH__` - while it will after this
patch. This will certainly break libunwind for linux on arm. (And prior to this
patch, `clang -x c -target armv7-netbsd -E -dM - < /dev/null` did include it,
but now it's only included when exceptions are enabled - I think the old
behaviour is preferrable wrt that as well.)
So, similarly how we on x86_64 have a default that enables SEH unless something
else has been specified, we need to prefer ARM EHABI on everything on ELF
except netbsd. I guess you could fold in the apple defaults into that as well?
Repository:
rL LLVM
https://reviews.llvm.org/D39673
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