[kpatch] [PATCH] livepatch-patch-hook: make callbacks addition depend on the kernel version

[Josh Poimboeuf]

On Thu, Apr 12, 2018 at 07:19:47PM +0300, Mike Rapoport wrote:
> Since commit 926e4e0c7d14b43896f9814da236b4d6408c8ff0 ("kmod: add support
> for in-kernel livepatch hooks") livepatch-patch-hook.c unconditionally
> creates callbacks. This causes build error for kernels older than 4.15:
> 
> make -C /home/rppt/git/linux M=/home/rppt/.kpatch/tmp/patch livepatch-proc-vmalloc-live.ko
> make[1]: Entering directory '/home/rppt/git/linux'
>   CC [M]  /home/rppt/.kpatch/tmp/patch/patch-hook.o
> In file included from /home/rppt/.kpatch/tmp/patch/patch-hook.c:21:0:
> /home/rppt/.kpatch/tmp/patch/livepatch-patch-hook.c:82:23: error: field ‘callbacks’ has incomplete type
>   struct klp_callbacks callbacks;
>                        ^
> /home/rppt/.kpatch/tmp/patch/livepatch-patch-hook.c: In function ‘patch_init’:
> /home/rppt/.kpatch/tmp/patch/livepatch-patch-hook.c:395:10: error: ‘struct klp_object’ has no member named ‘callbacks’
>    lobject->callbacks = object->callbacks;
>           ^
> scripts/Makefile.build:302: recipe for target '/home/rppt/.kpatch/tmp/patch/patch-hook.o' failed
> make[2]: *** [/home/rppt/.kpatch/tmp/patch/patch-hook.o] Error 1
> Makefile:1687: recipe for target 'livepatch-proc-vmalloc-live.ko' failed
> make[1]: *** [livepatch-proc-vmalloc-live.ko] Error 2
> make[1]: Leaving directory '/home/rppt/git/linux'
> Makefile:20: recipe for target 'livepatch-proc-vmalloc-live.ko' failed
> make: *** [livepatch-proc-vmalloc-live.ko] Error 2
> 
> Introduce HAVE_LIVEPATCH_CALLBACKS to allow conditional compilation of the
> callbacks addition.
> 
> Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>

Thanks!  There are a few typos in the patch: "HAS" vs "HAVE".  Would you
mind opening a pull request on github?

> ---
>  kmod/patch/livepatch-patch-hook.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/kmod/patch/livepatch-patch-hook.c b/kmod/patch/livepatch-patch-hook.c
> index f9e9f06..ecd00b2 100644
> --- a/kmod/patch/livepatch-patch-hook.c
> +++ b/kmod/patch/livepatch-patch-hook.c
> @@ -53,6 +53,14 @@
>  #define HAVE_IMMEDIATE
>  #endif
>  
> +#ifdef RHEL_RELEASE_CODE
> +# if RHEL_RELEASE_CODE >= RHEL_RELEASE_VERSION(7, 5)
> +#  define HAVE_LIVEPATCH_CALLBACKS
> +# endif
> +#elif LINUX_VERSION_CODE >= KERNEL_VERSION(4, 15, 0)
> +# define HAVE_LIVEPATCH_CALLBACKS
> +#endif
> +
>  /*
>   * There are quite a few similar structures at play in this file:
>   * - livepatch.h structs prefixed with klp_*
> @@ -79,7 +87,9 @@ struct patch_object {
>  	struct list_head list;
>  	struct list_head funcs;
>  	struct list_head relocs;
> +#ifdef HAS_LIVEPATCH_CALLBACKS
>  	struct klp_callbacks callbacks;
> +#endif
>  	const char *name;
>  	int funcs_nr, relocs_nr;
>  };
> @@ -211,6 +221,7 @@ static void patch_free_livepatch(struct klp_patch *patch)
>  	}
>  }
>  
> +#ifdef HAS_LIVEPATCH_CALLBACKS
>  extern struct kpatch_pre_patch_callback __kpatch_callbacks_pre_patch[], __kpatch_callbacks_pre_patch_end[];
>  extern struct kpatch_post_patch_callback __kpatch_callbacks_post_patch[], __kpatch_callbacks_post_patch_end[];
>  extern struct kpatch_pre_unpatch_callback __kpatch_callbacks_pre_unpatch[], __kpatch_callbacks_pre_unpatch_end[];
> @@ -286,6 +297,9 @@ static int add_callbacks_to_patch_objects(void)
>  
>  	return 0;
>  }
> +#else /* HAS_LIVEPATCH_CALLBACKS */
> +static inline int add_callbacks_to_patch_objects(void) { return 0; }
> +#endif /* HAS_LIVEPATCH_CALLBACKS */
>  
>  extern struct kpatch_patch_func __kpatch_funcs[], __kpatch_funcs_end[];
>  #ifndef HAVE_ELF_RELOCS
> @@ -392,7 +406,9 @@ static int __init patch_init(void)
>  		}
>  #endif /* HAVE_ELF_RELOCS */
>  
> +#ifdef HAVE_LIVEPATCH_CALLBACKS
>  		lobject->callbacks = object->callbacks;
> +#endif
>  
>  		i++;
>  	}
> -- 
> 2.7.4
> 

-- 
Josh