From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CE7881DA4E for ; Fri, 28 Mar 2025 15:19:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743175175; cv=none; b=cYL+AMAXxlqHXtfLpThjqRaBadTRCk6UDhqnjWbEIuEysZVhRBGYgsnqqg66/SjFnGiRK4bdcdrUqalATfVavIuTkIG3pm0OyEywHZuualCmFC/nCer0J+m0f4DqZJYpsQOS0dXvkc+2XsAp5eiXAuRLjaM0ACgfr6L6NFqew+Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743175175; c=relaxed/simple; bh=fxZCLV8naClLk0aWX5RfGrSNISKmuMfNpeQcSU2Cx7M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ka9ZarCs3YYAk9Z31HUgZNWGyUh+HKDZnxCYNZIHHTFH9PGY3Y/Ok0DUt2Sb5vzySmGXvxe5PxPcoukSlsebG4p8lNOXaTQ5CCJwefXYgjWbHRq4kN2+H/2l173LJ3sAFr2dSfUjpx6No7R7N7F9WmQL3qQW4zOw26QiciLyfs4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lqUw2Q+T; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lqUw2Q+T" Message-ID: <4c60f56a-8505-49f3-872b-d485d65813d7@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1743175167; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iSngOmVMoweaaJAhBuXF0RhHXq8OxThWJRjs/X3LC3A=; b=lqUw2Q+TLgVHyUO7wc+z9fqTaCjFaLUf/tY9mI7WWb5CAb8jGfhKYsXXWL6m0DOu/dATGG HD69Ds5unoyNRq02SvIku80BQGUtZwCq9xEpWXhy6GriCid6Btw9KVb/L2H6lN8G6GMIN+ hHxAlbvADNtLnOYZ5GX/Q9GiOy5mo3c= Date: Fri, 28 Mar 2025 23:19:09 +0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: Question: fentry on kernel func optimized by compiler To: Song Liu Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Jiri Olsa , Yonghong Song , bpf , Alan Maguire References: <7e46c811-e85b-4001-8fac-b16aa0e9815f@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Tao Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2025/3/28 01:19, Song Liu 写道: > Hi Tao, > > Compiler optimizations can cause issues for tracing kernel functions. Please > refer to Yonghong and Alan's presentation [1] for various cases. > > Thanks, > Song > > [1] https://lpc.events/event/18/contributions/1945/ > > Hi Song, Thank you for the materials you provided. I'll take a look at them. > On Thu, Mar 27, 2025 at 9:03 AM Tao Chen wrote: >> >> Hi, >> >> I recently encountered a problem when using fentry to trace kernel >> functions optimized by compiler, the specific situation is as follows: >> https://github.com/bpftrace/bpftrace/issues/3940 >> >> Simply put, some functions have been optimized by the compiler. The >> original function names are found through BTF, but the optimized >> functions are the ones that exist in kallsyms_lookup_name. Therefore, >> the two do not match. >> >> func_proto = btf_type_by_id(desc_btf, func->type); >> if (!func_proto || !btf_type_is_func_proto(func_proto)) { >> verbose(env, "kernel function btf_id %u does not have a >> valid func_proto\n", >> func_id); >> return -EINVAL; >> } >> >> func_name = btf_name_by_offset(desc_btf, func->name_off); >> addr = kallsyms_lookup_name(func_name); >> if (!addr) { >> verbose(env, "cannot find address for kernel function >> %s\n", >> func_name); >> return -EINVAL; >> } >> >> I have made a simple statistics and there are approximately more than >> 2,000 functions in Ubuntu 24.04. >> >> dylane@2404:~$ cat /proc/kallsyms | grep isra | wc -l >> 2324 >> >> So can we add a judgment from libbpf. If it is an optimized function, >> pass the suffix of the optimized function from the user space to the >> kernel, and then perform a function name concatenation, like: >> >> func_name = btf_name_by_offset(desc_btf, func->name_off); >> if (optimize) { >> func_name = func_name + ".isra.0" >> } >> addr = kallsyms_lookup_name(func_name); >> >> -- >> Best Regards >> Tao Chen >> -- Best Regards Tao Chen