[Bug target/92287] Mismatches in the calling convention for zero sized types

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92287

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |segher at gcc dot gnu.org

--- Comment #6 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Bill Schmidt from comment #5)
> For the 32-bit ELF ABI, all structs (regardless of size) are passed using a
> pointer allowing for call-by-value semantics.  This is the source of ZSTs
> requiring a register.  So it's clear there is an ABI that requires this
> behavior.  (Look for the Parameter Passing Register Selection Algorithm in
> https://github.com/ryanarn/powerabi/blob/master/chap3-elf32abi.sgml.)
> 
> The 64-bit ABIs (both ELF V1 and ELF V2) pass structures in registers, and
> the parameter passing algorithms won't assign registers for size-0
> aggregates.  This is intentional.

Yup.  And everything is identical between LE and BE on all these ABIs.

Note that the situation for zero-sized structs isn't very clear in
most ABIs, these included.  You must have an unusual program if this
ever matters ;-)