Re: [RFC PATCH 4/8] powerpc/ppc_asm: use plain numbers for registers
flat view
From: Segher Boessenkool <hidden>
Date: 2021-02-25 15:28:19
On Thu, Feb 25, 2021 at 02:10:02PM +1100, Daniel Axtens wrote:
This is dumb but makes the llvm integrated assembler happy. https://github.com/ClangBuiltLinux/linux/issues/764
-#define r0 %r0
+#define r0 0
This is a big step back (compare 9a13a524ba37).
If you use a new enough GAS, you can use the -mregnames option and just
say "r0" directly (so not define it at all, or define it to itself).
===
addi 3,3,3
addi r3,r3,3
addi %r3,%r3,3
addi 3,3,3
addi r3,r3,r3
addi %r3,%r3,%r3
===
$ as t.s -o t.o -mregnames
t.s: Assembler messages:
t.s:6: Warning: invalid register expression
t.s:7: Warning: invalid register expression
Many people do not like bare numbers. It is a bit like not wearing
seatbelts (but so is all assembler code really: you just have to pay
attention). A better argument is that it is harder to read for people
not used to assembler code like this.
We used to have "#define r0 0" etc., and that was quite problematic.
Like that "addi r3,r3,r3" example, but also, people wrote "r0" where
only a plain 0 is allowed (like in "lwzx r3,0,r3": "r0" would be
misleading there!)
Segher