[PATCH] D61950: [PowerPC64] adds ABI parsing when specified on target triple

Thu May 16 06:28:47 PDT 2019

adalava marked an inline comment as done.
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In D61950#1504169 <https://reviews.llvm.org/D61950#1504169>, @MaskRay wrote:

> Will FreeBSD 13 or future releases support ELFv1? If not, it may be cleaner to not invent `-elfv2` `-elfv1` triples, but rather dispatch on the major version, e.g. `powerpc64-unknown-freebsd13.0` could mean ELFv2.

Invent  `-elfv2` `-elfv1` and make it used by default is not the goal here but add ABI target triple support. Discussions at #llvm <https://reviews.llvm.org/tag/llvm/> IRC channel shown that provide ABI in target triple is more acceptable than using `-mabi=elfv2`, so this patch is for when you want and ABI other than default (that was based on <arch>, <os> or <os_version>)

For FreeBSD, in the future default ABI will be decided based on OS version on triple  `powerpc64-unknown-freebsd<os_version>`. However, there's currently no agreement on what will be that <os_version>. As 13.0 is currently ELFv1, so LLVM couldn't assume 13.0 is ELFv2 at this moment.

So, during the transition period, developers could use TARGET_ABI variable to build the FreeBSD PPC64 ELFv2 version. As example,  building FreeBSD with `make TARGET=powerpc TARGET_ARCH=powerpc64 TARGET_ABI=elfv2`, where it's expected to form a target triple like `powerpc64-unknown-freebsd13.0-elfv2`, based on "<arch><sub>-<vendor>-<sys>-<abi>" definition. That is passed right away to clang.

If it's not possible, we would have to patch FreeBSD makefiles to not use TARGET_ABI variable value when TARGET_ARCH is powerpc64, and append -mabi=elfv2 instead. This sounds feasible, however clang running on final ELFv2 userland won't know it's on ELFv2 and users will need to specify `-mabi=elfv2` and CFLAGS/CXXFLAGS to compile applications. This is unfeasible, specially for FreeBSD ports, as many packages didn't handle these variables correctly.

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