selftests/powerpc/ptrace: Do more of ptrace-gpr in asm

The ptrace-gpr test includes some inline asm to load GPR and FPR
registers. It then goes back to C to wait for the parent to trace it and
then checks register contents.

The split between inline asm and C is fragile, it relies on the compiler
not using any non-volatile GPRs after the inline asm block. It also
requires a very large and unwieldy inline asm block.

So convert the logic to set registers, wait, and store registers to a
single asm function, meaning there's no window for the compiler to
intervene.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220627140239.2464900-10-mpe@ellerman.id.au

tools/testing/selftests/powerpc/include/basic_asm.h

@@ -94,4 +94,12 @@
 	PPC_LL	r0, STACK_FRAME_LR_POS(%r1); \
 	mtlr	r0;
 
+.macro OP_REGS op, reg_width, start_reg, end_reg, base_reg, base_reg_offset=0, skip=0
+	.set i, \start_reg
+	.rept (\end_reg - \start_reg + 1)
+	\op	i, (\reg_width * (i - \skip) + \base_reg_offset)(\base_reg)
+	.set i, i + 1
+	.endr
+.endm
+
 #endif /* _SELFTESTS_POWERPC_BASIC_ASM_H */