Hi Florian, > On 10 Jan 2022, at 08:38, Florian Weimer <fwei...@redhat.com> wrote: > > * Jeff Law via Gcc: > >> Most targets these days use registers for parameter passing and >> obviously we can run out of registers on all of them. The key >> property is the size/alignment of the argument differs depending on if >> it's pass in a register (get promoted) or passed in memory (not >> promoted). I'm not immediately aware of another ABI with that >> feature. Though I haven't really gone looking. > > I think what AArch64 Darwin does is not compatible with a GCC extension > that allows calling functions defined with a prototype without it (for > pre-ISO-C compatibility).
AFAIU the implementation: In the case that a call is built and no prototype is available, the assumption is that all parms are named. The promotion is then done according to the C promotion rules. [for the number of args that can be passed in int regs] the callee will happen to observe the same rules in this case. It will, however, break once we overflow the number of int regs.. :/ ==== The case that is fundamentally broken from scratch is of a variadic function called without a prototype - since the aarch64-darwin ABI places unnamed parms differently. So that the absence of a prototype causes us to place all args as if they were named. ==== Wmissing-prototype Wstrict-prototypes would wisely be promoted to errors for this platform, (the ABI is obviously not up for change, since it’s already on millions of devices). > Given that, anyone defining an ABI in > parallel with a GCC implementation probably has paused, reconsidered > what they were doing, My guess is that this step was omitted - i.e. the port was designed in the LLVM framework. I can raise a query with the ABI owners, I guess. > and adjusted the ABI for K&R compatibility. FWIW, we bootstrap sucessfully including the K&R code in intl/ Given we have 8 int regs available, probably many calls will work .. ==== As of now, I must assume that what is broken by the cases above will remain broken, and I just need to find a way to implement the cases that will work (i.e. when proper prototypes are available) thanks Iain
