Re: [PATCH bpf-next v7 02/13] tools/resolve_btfids: Add support for 8-byte BTF sets

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Jul 21, 2022 at 03:42:34PM +0200, Kumar Kartikeya Dwivedi wrote:
> A flag is a 4-byte symbol that may follow a BTF ID in a set8. This is
> used in the kernel to tag kfuncs in BTF sets with certain flags. Add
> support to adjust the sorting code so that it passes size as 8 bytes
> for 8-byte BTF sets.
> 
> Cc: Jiri Olsa <jolsa@kernel.org>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  tools/bpf/resolve_btfids/main.c | 40 ++++++++++++++++++++++++++++-----
>  1 file changed, 34 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
> index 5d26f3c6f918..80cd7843c677 100644
> --- a/tools/bpf/resolve_btfids/main.c
> +++ b/tools/bpf/resolve_btfids/main.c
> @@ -45,6 +45,19 @@
>   *             .zero 4
>   *             __BTF_ID__func__vfs_fallocate__4:
>   *             .zero 4
> + *
> + *   set8    - store symbol size into first 4 bytes and sort following
> + *             ID list
> + *
> + *             __BTF_ID__set8__list:
> + *             .zero 8
> + *             list:
> + *             __BTF_ID__func__vfs_getattr__3:
> + *             .zero 4
> + *	       .word (1 << 0) | (1 << 2)
> + *             __BTF_ID__func__vfs_fallocate__5:
> + *             .zero 4
> + *	       .word (1 << 3) | (1 << 1) | (1 << 2)
>   */
>  
>  #define  _GNU_SOURCE
> @@ -72,6 +85,7 @@
>  #define BTF_TYPEDEF	"typedef"
>  #define BTF_FUNC	"func"
>  #define BTF_SET		"set"
> +#define BTF_SET8	"set8"
>  
>  #define ADDR_CNT	100
>  
> @@ -84,6 +98,7 @@ struct btf_id {
>  	};
>  	int		 addr_cnt;
>  	bool		 is_set;
> +	bool		 is_set8;
>  	Elf64_Addr	 addr[ADDR_CNT];
>  };
>  
> @@ -231,14 +246,14 @@ static char *get_id(const char *prefix_end)
>  	return id;
>  }
>  
> -static struct btf_id *add_set(struct object *obj, char *name)
> +static struct btf_id *add_set(struct object *obj, char *name, bool is_set8)
>  {
>  	/*
>  	 * __BTF_ID__set__name
>  	 * name =    ^
>  	 * id   =         ^
>  	 */
> -	char *id = name + sizeof(BTF_SET "__") - 1;
> +	char *id = name + (is_set8 ? sizeof(BTF_SET8 "__") : sizeof(BTF_SET "__")) - 1;
>  	int len = strlen(name);
>  
>  	if (id >= name + len) {
> @@ -444,9 +459,21 @@ static int symbols_collect(struct object *obj)
>  		} else if (!strncmp(prefix, BTF_FUNC, sizeof(BTF_FUNC) - 1)) {
>  			obj->nr_funcs++;
>  			id = add_symbol(&obj->funcs, prefix, sizeof(BTF_FUNC) - 1);
> +		/* set8 */
> +		} else if (!strncmp(prefix, BTF_SET8, sizeof(BTF_SET8) - 1)) {
> +			id = add_set(obj, prefix, true);
> +			/*
> +			 * SET8 objects store list's count, which is encoded
> +			 * in symbol's size, together with 'cnt' field hence
> +			 * that - 1.
> +			 */
> +			if (id) {
> +				id->cnt = sym.st_size / sizeof(uint64_t) - 1;
> +				id->is_set8 = true;
> +			}
>  		/* set */
>  		} else if (!strncmp(prefix, BTF_SET, sizeof(BTF_SET) - 1)) {
> -			id = add_set(obj, prefix);
> +			id = add_set(obj, prefix, false);
>  			/*
>  			 * SET objects store list's count, which is encoded
>  			 * in symbol's size, together with 'cnt' field hence
> @@ -571,7 +598,8 @@ static int id_patch(struct object *obj, struct btf_id *id)
>  	int *ptr = data->d_buf;
>  	int i;
>  
> -	if (!id->id && !id->is_set)
> +	/* For set, set8, id->id may be 0 */
> +	if (!id->id && !id->is_set && !id->is_set8)
>  		pr_err("WARN: resolve_btfids: unresolved symbol %s\n", id->name);
>  
>  	for (i = 0; i < id->addr_cnt; i++) {
> @@ -643,13 +671,13 @@ static int sets_patch(struct object *obj)
>  		}
>  
>  		idx = idx / sizeof(int);
> -		base = &ptr[idx] + 1;
> +		base = &ptr[idx] + (id->is_set8 ? 2 : 1);
>  		cnt = ptr[idx];
>  
>  		pr_debug("sorting  addr %5lu: cnt %6d [%s]\n",
>  			 (idx + 1) * sizeof(int), cnt, id->name);
>  
> -		qsort(base, cnt, sizeof(int), cmp_id);
> +		qsort(base, cnt, id->is_set8 ? sizeof(uint64_t) : sizeof(int), cmp_id);
>  
>  		next = rb_next(next);
>  	}
> -- 
> 2.34.1
>