From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 497C7EE4996 for ; Tue, 22 Aug 2023 13:37:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230029AbjHVNhn (ORCPT ); Tue, 22 Aug 2023 09:37:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59472 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235676AbjHVNhn (ORCPT ); Tue, 22 Aug 2023 09:37:43 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5B0AD1B9; Tue, 22 Aug 2023 06:37:41 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id DC69D629D8; Tue, 22 Aug 2023 13:37:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C1EBC433C9; Tue, 22 Aug 2023 13:37:33 +0000 (UTC) Date: Tue, 22 Aug 2023 09:37:20 -0400 From: Steven Rostedt To: "Masami Hiramatsu (Google)" Cc: linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Martin KaFai Lau , bpf@vger.kernel.org, Sven Schnelle , Alexei Starovoitov Subject: Re: [PATCH v5 3/9] tracing/probes: Add a function to search a member of a struct/union Message-ID: <20230822093720.016c3554@rorschach.local.home> In-Reply-To: <169137689818.271367.4200174950023036516.stgit@devnote2> References: <169137686814.271367.11218568219311636206.stgit@devnote2> <169137689818.271367.4200174950023036516.stgit@devnote2> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org On Mon, 7 Aug 2023 11:54:58 +0900 "Masami Hiramatsu (Google)" wrote: > --- a/kernel/trace/trace_btf.c > +++ b/kernel/trace/trace_btf.c > @@ -50,3 +50,60 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s3 > return NULL; > } > > +#define BTF_ANON_STACK_MAX 16 > + > +/* > + * Find a member of data structure/union by name and return it. > + * Return NULL if not found, or -EINVAL if parameter is invalid. > + * If the member is an member of anonymous union/structure, the offset > + * of that anonymous union/structure is stored into @anon_offset. Caller > + * can calculate the correct offset from the root data structure by > + * adding anon_offset to the member's offset. > + */ > +const struct btf_member *btf_find_struct_member(struct btf *btf, > + const struct btf_type *type, > + const char *member_name, > + u32 *anon_offset) > +{ > + struct { > + u32 tid; > + u32 offset; > + } anon_stack[BTF_ANON_STACK_MAX]; Where is this called as the above is 128 bytes, which is a bit large for the stack. It may not be bad if it's not that generic of a function. But if the stack is getting tight, this could still be an issue. -- Steve > + const struct btf_member *member; > + u32 tid, cur_offset = 0; > + const char *name; > + int i, top = 0; > + > +retry: > + if (!btf_type_is_struct(type)) > + return ERR_PTR(-EINVAL); > + > + for_each_member(i, type, member) { > + if (!member->name_off) { > + /* Anonymous union/struct: push it for later use */ > + type = btf_type_skip_modifiers(btf, member->type, &tid); > + if (type && top < BTF_ANON_STACK_MAX) { > + anon_stack[top].tid = tid; > + anon_stack[top++].offset = > + cur_offset + member->offset; > + } > + } else { > + name = btf_name_by_offset(btf, member->name_off); > + if (name && !strcmp(member_name, name)) { > + if (anon_offset) > + *anon_offset = cur_offset; > + return member; > + } > + } > + } > + if (top > 0) { > + /* Pop from the anonymous stack and retry */ > + tid = anon_stack[--top].tid; > + cur_offset = anon_stack[top].offset; > + type = btf_type_by_id(btf, tid); > + goto retry; > + } > + > + return NULL; > +} > +