Re: [PATCH 1/9] powerpc/lib: Add helper to check if offset is within conditional branch range

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

Le 01/10/2021 à 23:14, Naveen N. Rao a écrit :
> Add a helper to check if a given offset is within the branch range for a
> powerpc conditional branch instruction, and update some sites to use the
> new helper.
> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
>   arch/powerpc/include/asm/code-patching.h | 1 +
>   arch/powerpc/lib/code-patching.c         | 7 ++++++-
>   arch/powerpc/net/bpf_jit.h               | 7 +------
>   3 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
> index a95f63788c6b14..4ba834599c4d4c 100644
> --- a/arch/powerpc/include/asm/code-patching.h
> +++ b/arch/powerpc/include/asm/code-patching.h
> @@ -23,6 +23,7 @@
>   #define BRANCH_ABSOLUTE	0x2
>   
>   bool is_offset_in_branch_range(long offset);
> +bool is_offset_in_cond_branch_range(long offset);
>   int create_branch(struct ppc_inst *instr, const u32 *addr,
>   		  unsigned long target, int flags);
>   int create_cond_branch(struct ppc_inst *instr, const u32 *addr,
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> index f9a3019e37b43c..e2342b9a1ab9c9 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -228,6 +228,11 @@ bool is_offset_in_branch_range(long offset)
>   	return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3));
>   }
>   
> +bool is_offset_in_cond_branch_range(long offset)
> +{
> +	return offset >= -0x8000 && offset <= 0x7FFF && !(offset & 0x3);
> +}

Would be better without capital letters in numbers, in extenso 0x7fff 
instead of 0x7FFF

> +
>   /*
>    * Helper to check if a given instruction is a conditional branch
>    * Derived from the conditional checks in analyse_instr()
> @@ -280,7 +285,7 @@ int create_cond_branch(struct ppc_inst *instr, const u32 *addr,
>   		offset = offset - (unsigned long)addr;
>   
>   	/* Check we can represent the target in the instruction format */
> -	if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
> +	if (!is_offset_in_cond_branch_range(offset))
>   		return 1;
>   
>   	/* Mask out the flags and target, so they don't step on each other. */
> diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
> index 99fad093f43ec1..935ea95b66359e 100644
> --- a/arch/powerpc/net/bpf_jit.h
> +++ b/arch/powerpc/net/bpf_jit.h
> @@ -78,11 +78,6 @@
>   #define PPC_FUNC_ADDR(d,i) do { PPC_LI32(d, i); } while(0)
>   #endif
>   
> -static inline bool is_nearbranch(int offset)
> -{
> -	return (offset < 32768) && (offset >= -32768);
> -}
> -
>   /*
>    * The fly in the ointment of code size changing from pass to pass is
>    * avoided by padding the short branch case with a NOP.	 If code size differs
> @@ -91,7 +86,7 @@ static inline bool is_nearbranch(int offset)
>    * state.
>    */
>   #define PPC_BCC(cond, dest)	do {					      \
> -		if (is_nearbranch((dest) - (ctx->idx * 4))) {		      \
> +		if (is_offset_in_cond_branch_range((long)(dest) - (ctx->idx * 4))) {	\
>   			PPC_BCC_SHORT(cond, dest);			      \
>   			EMIT(PPC_RAW_NOP());				      \
>   		} else {						      \
>