I'm trying to understand which ABIs are supported in the PowerPC
backend and I'm getting a bit confused. Here's what I've gathered so
far alongside with some questions.
Sorry for the confusion, this all should probably be cleaned up a bit.
In general, LLVM today supports the following ABIs:
- The Darwin ABI (32-bit and 64-bit flavors)
- The 32-bit SVR4 ABI
- Two variants of the 64-bit SVR4 ABI: ELFv1 and ELFv2
The ELFv1 ABI is used on 64-bit big-endian Linux and AIX.
The ELFv2 ABI is used on 64-bit little-endian Linux.
Unfortunately, the term "SVR4" is quite overloaded, and applies
both to the 32-bit and the 64-bit ABIs, even though they are
quite different. "ELF ABI" is used interchangably with "SVR4 ABI".
ELFv1 is a recently introduced term to refer to what was previously
just called the ELF ABI (or equivalently SVR4 ABI); it is now used
to refer to the *old* variant of the ELF ABI as opposed to the new
- In PPCSubtarget.h there's DarwinABI, SVR4ABI and ELFv2ABI.
- The CodeGenerator documentation claims that the AIX PowerPC ABI is
followed (with some deviations). Is this refering to the DarwinABI?
No, that's the ELFv1 ABI.
- In a recent commit a TargetABI value and enumeration was added to
PPCSubtarget which contains PPC_ABI_UNKNOWN, PPC_ABI_ELFv1 and
PPC_ABI_ELFv2. For 64-bit non-Darwin the TargetABI value is set to
either ELF-variant in resetSubtargetFeatures(...) based on endianess
(unless explicitly set previously). As I understand it ELFv2 is a new
ABI but which ABI does ELFv1 map to?
I hope the above makes it clearer.
- Since isSVR4ABI() is defined as !isDarwin() it currently is possible
for SVR4 and ELFv2 to be true at the same time which doesn't seem
correct to me.
isSVR4ABI is true for either ELFv1 or ELFv2, and also for the 32-bit
SVR4 ABI. This should probably be cleaned up by having three separate
- My understanding of SVR4ABI have been that it is the 32-bit PPC
processor supplement from Sun. Is this correct? If so, which ABI is
used for 64-bit non-Darwin?
SVR4 has always been used for either the 32-bit or 64-bit ELF ABIs
(*both* are processor supplement documents based on the original
Sun ELF/SVR4 ABI).
I'm trying to implement the PPC EABI (which is based on the SVR4ABI)
for an out-of-tree subtarget which means I need to understand the
current status a bit better.
It's up to Hal, but I'd suggest to split up the isSVR4ABI predicate
into three separate options, e.g. isSVR4ABI (or maybe isSVR4_32ABI),
isELFv1ABI, and isELFv2ABI; and then add another one for your new