Re: [PATCH v6 8/9] Implement kernel live patching for ppc64le (ABIv2)

[Miroslav Benes]

[ added Petr to CC list ]

On Mon, 25 Jan 2016, Torsten Duwe wrote:

>   * create the appropriate files+functions
>     arch/powerpc/include/asm/livepatch.h
>         klp_check_compiler_support,
>         klp_arch_set_pc
>     arch/powerpc/kernel/livepatch.c with a stub for
>         klp_write_module_reloc
>     This is architecture-independent work in progress.
>   * introduce a fixup in arch/powerpc/kernel/entry_64.S
>     for local calls that are becoming global due to live patching.
>     And of course do the main KLP thing: return to a maybe different
>     address, possibly altered by the live patching ftrace op.
> 
> Signed-off-by: Torsten Duwe <duwe@xxxxxxx>

Hi,

I have a few questions...

We still need Petr's patch from [1] to make livepatch work, right? Could 
you, please, add it to this patch set to make it self-sufficient?

Second, what is the situation with mcount prologue between gcc < 6 and 
gcc-6? Are there only 12 bytes in gcc-6 prologue? If yes, we need to 
change Petr's patch to make it more general and to be able to cope with 
different prologues. This is unfortunate. Either way, please mention it 
somewhere in a changelog.

I haven't reviewed the patch properly yet, but there is a comment below.

[1] http://lkml.kernel.org/g/20151203160004.GE8047@xxxxxxxxxxxxxxx

> +/**
> + * klp_write_module_reloc() - write a relocation in a module
> + * @mod:       module in which the section to be modified is found
> + * @type:      ELF relocation type (see asm/elf.h)
> + * @loc:       address that the relocation should be written to
> + * @value:     relocation value (sym address + addend)
> + *
> + * This function writes a relocation to the specified location for
> + * a particular module.
> + */
> +int klp_write_module_reloc(struct module *mod, unsigned long type,
> +			    unsigned long loc, unsigned long value)
> +{
> +	/* This requires infrastructure changes; we need the loadinfos. */
> +	pr_err("lpc_write_module_reloc not yet supported\n");

This is a nit, but there is no lpc_write_module_reloc. It should be 
klp_write_module_reloc.

Thanks,
Miroslav