Re: [PATCH v3 1/6] powerpc/code-patching: Implement generic text patching function

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 06/10/2022 à 05:36, Benjamin Gray a écrit :
> On Wed, 2022-10-05 at 17:55 +0000, Christophe Leroy wrote:
>> I'm on business trip this week so I can't test it on hardware, but
>> the
>> generated code looks horrid and sub-optimal, with a stack frame and
>> so
>> many registers saved into it. That's mpc885_ads_defconfig built with
>> GCC
>> 12, without modules without stackprotector with 4k pages.
> 
> Yeah, that definitely wasn't supposed to happen. I was looking at the
> 32 and 64 bit machine code closely while actively writing it, but I
> must have refactored it badly when cleaning up for submission. It was
> supposed to automatically be inlined, leaving it identical to the
> original on 32-bit.
> 
> Given inlining is desirable here, and 64-bit inlines anyway, I think I
> should just mark __patch_memory with __always_inline.

FWIW, I get a far better result with :

diff --git a/arch/powerpc/lib/code-patching.c 
b/arch/powerpc/lib/code-patching.c
index ba00c550d9d2..447b8de6e427 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -21,7 +21,7 @@ static int __patch_memory(void *patch_addr, unsigned 
long val, void *exec_addr,
  	/* Prefixed instruction may cross cacheline if cacheline smaller than 
64 bytes */
  	BUILD_BUG_ON(IS_ENABLED(CONFIG_PPC64) && L1_CACHE_BYTES < 64);

-	if (unlikely(is_dword))
+	if (IS_ENABLED(CONFIG_PPC64) && unlikely(is_dword))
  		__put_kernel_nofault(patch_addr, &val, u64, failed);
  	else
  		__put_kernel_nofault(patch_addr, &val, u32, failed);