[PATCH 05/14] powerpc: Add new code patching routines

[Kumar Gala]

On Jun 23, 2008, at 8:32 PM, Michael Ellerman wrote:

> This commit adds some new routines for patching code, they will be  
> used
> in a following commit.
>
> Signed-off-by: Michael Ellerman <michael at ellerman.id.au>
> ---
> arch/powerpc/lib/code-patching.c    |  107 ++++++++++++++++++++++++++ 
> +++++++++
> include/asm-powerpc/code-patching.h |    8 +++
> 2 files changed, 115 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/ 
> code-patching.c
> index 430f4c1..27957c4 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -41,3 +41,110 @@ unsigned int create_branch(const unsigned int  
> *addr,
>
> 	return instruction;
> }
> +
> +unsigned int create_cond_branch(const unsigned int *addr,
> +				unsigned long target, int flags)
> +{

it would be nice to have some idea what flags is suppose to be.
>
> +	unsigned int instruction;
> +	long offset;
> +
> +	offset = target;
> +	if (! (flags & BRANCH_ABSOLUTE))
> +		offset = offset - (unsigned long)addr;
> +
> +	/* Check we can represent the target in the instruction format */
> +	if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
> +		return 0;
> +
> +	/* Mask out the flags and target, so they don't step on each  
> other. */
> +	instruction = 0x40000000 | (flags & 0x3FF0003) | (offset & 0xFFFC);
> +
> +	return instruction;
> +}

[snip]

> +unsigned int translate_branch(const unsigned int *dest, const  
> unsigned int *src)
> +{

I'm not sure I get what this function is trying to do.

>
> +	unsigned long target;
> +
> +	target = branch_target(src);
> +
> +	if (instr_is_branch_iform(*src))
> +		return create_branch(dest, target, *src);
> +	else if (instr_is_branch_bform(*src))
> +		return create_cond_branch(dest, target, *src);
> +
> +	return 0;
> +}