On Tue, Jun 18, 2019 at 12:19:51PM +0200, Florian Weimer wrote: > For example, on POWER, the condition register is used to indicate > errors. Instead of using that directly, we need to store that in a > register, via mfcr:
Hrm, that example shows that my suggestion in https://gcc.gnu.org/ml/gcc/2019-06/msg00170.html needs to be extended a bit, for multiple return values. We usually do extra return values for builtins via an extra pointer; here, that cannot come as last argument though, the call args are varargs. So I suggested a generic builtin retval = __builtin_syscall (STYLE, syscall_nr, arg0, arg1, ...); but that should for PowerPC syscalls be retval = __builtin_syscall (STYLE, &err, syscall_nr, arg0, arg1, ...); Generically it it just retval = __builtin_syscall (STYLE, args...); (or without retval, if the target decides this style call has no retval?) > 0000000000000000 <__GI___getdents64>: > 0: addis r2,r12,0 > 0: R_PPC64_REL16_HA .TOC. > 4: addi r2,r2,0 > 4: R_PPC64_REL16_LO .TOC.+0x4 > 8: li r0,202 > c: sc > 10: mfcr r0 You also get this mfcr if the error code isn't used currently, even. And it uses mfcr always it seems, not mfocrf, or directly use the bit like in a conditional branch insn or an isel or whatnot. > Ideally, the mfcr, andis, beqlr instructions would just be a bclr > instruction. Yup. Segher
