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

Le 06/10/2022 à 05:36, Benjamin Gray a écrit :

quoted

On Wed, 2022-10-05 at 17:55 +0000, Christophe Leroy wrote:

quoted

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);