From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (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 0570C1DE2BC for ; Tue, 29 Jul 2025 22:54:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753829686; cv=none; b=rAu4ynrbV2hM+jOVsHFy/rabLeT3CzbdMoLYfgwk7zap26ZuBi61NWWgn59d1wQAp3vrW6tORzlqRFX4rPA7WHh5b7rAT9M1bTY5pRwXYSHMoTzpDM7WfdtEcRdhxoYE0ywlN+4YDIcQhRbSnSaJKM4O90CsBtfchI25SQaWOho= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753829686; c=relaxed/simple; bh=SOB/o1iuwBQz2Y81Uao0nWrVWivItWtYYSlGD/JY1UQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Bzy0Mzo8dLNCfchQ+t6n9sEytzeN6m8xUcXJfQ8a2zjlhTbM8ke1QZqCIZx6BSO9R6nOTShHiao2O9xIDwn2rbfj15CENI03cPrqmcX5+3mKqvVuYf0f220oVTCt464nnj0kzCGWQzdAfG93xdtczI+SQkdKtQ0PJ3DSN8IJqpY= 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=gWaArqh1; arc=none smtp.client-ip=95.215.58.182 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="gWaArqh1" Message-ID: <23caf44c-48e7-41b2-bc9a-e286f93bd96f@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1753829682; 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=vR4nQsxlk4hEmvm6cSvy4y/DxKWhjZh62EU3mdesfDI=; b=gWaArqh1gSMDugR5FFecY/eAWa4VoEiDOtvPvfUEsQqRgx7spmxn/nATg8TFQlcI2A6X5g Ce0cGYtEvw51oaXJCVhQEsdIVUl7DBkk/z7BGKuSC94NU0hnlHsBRsxKXHoUlwQv2c2FjC jz2RoWPahdqttNVQzhvignn8it6KEPM= Date: Tue, 29 Jul 2025 15:54:31 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3] libbpf: fix USDT SIB argument handling causing unrecognized register error Content-Language: en-GB To: Jiawei Zhao , andrii@kernel.org Cc: bpf@vger.kernel.org References: <20250729161722.35462-1-Phoenix500526@163.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20250729161722.35462-1-Phoenix500526@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 7/29/25 9:17 AM, Jiawei Zhao wrote: > On x86-64, USDT arguments can be specified using Scale-Index-Base (SIB) > addressing, e.g. "1@-96(%rbp,%rax,8)". The current USDT implementation > in libbpf cannot parse this format, causing `bpf_program__attach_usdt()` > to fail with -ENOENT (unrecognized register). > > This patch fixes this by implementing the necessary changes: > - add correct handling for SIB-addressed arguments in `bpf_usdt_arg`. > - add adaptive support to `__bpf_usdt_arg_type` and > `__bpf_usdt_arg_spec` to represent SIB addressing parameters. > > Change since v1(https://lore.kernel.org/lkml/20250729125244.28364-1-Phoenix500526@163.com/): > - refactor the code to make it more readable > - modify the commit message to explain why and how > > Change since v2: > - fix the `scale` uninitialized error > > Signed-off-by: Jiawei Zhao > --- > tools/lib/bpf/usdt.bpf.h | 33 ++++++++++++++++++++++++++++++++- > tools/lib/bpf/usdt.c | 26 +++++++++++++++++++++++--- > 2 files changed, 55 insertions(+), 4 deletions(-) > > diff --git a/tools/lib/bpf/usdt.bpf.h b/tools/lib/bpf/usdt.bpf.h > index 2a7865c8e3fe..246513088c3a 100644 > --- a/tools/lib/bpf/usdt.bpf.h > +++ b/tools/lib/bpf/usdt.bpf.h > @@ -34,6 +34,7 @@ enum __bpf_usdt_arg_type { > BPF_USDT_ARG_CONST, > BPF_USDT_ARG_REG, > BPF_USDT_ARG_REG_DEREF, > + BPF_USDT_ARG_SIB, > }; > > struct __bpf_usdt_arg_spec { > @@ -43,6 +44,10 @@ struct __bpf_usdt_arg_spec { > enum __bpf_usdt_arg_type arg_type; > /* offset of referenced register within struct pt_regs */ > short reg_off; > + /* offset of index register in pt_regs, only used in SIB mode */ > + short idx_reg_off; > + /* scale factor for index register, only used in SIB mode */ > + short scale; > /* whether arg should be interpreted as signed value */ > bool arg_signed; > /* number of bits that need to be cleared and, optionally, > @@ -149,7 +154,7 @@ int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res) > { > struct __bpf_usdt_spec *spec; > struct __bpf_usdt_arg_spec *arg_spec; > - unsigned long val; > + unsigned long val, idx; > int err, spec_id; > > *res = 0; > @@ -202,6 +207,32 @@ int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res) > return err; > #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ > val >>= arg_spec->arg_bitshift; > +#endif > + break; > + case BPF_USDT_ARG_SIB: > + /* Arg is in memory addressed by SIB (Scale-Index-Base) mode > + * (e.g., "-1@-96(%rbp,%rax,8)" in USDT arg spec). Register > + * is identified like with BPF_USDT_ARG_SIB case, the offset > + * is in arg_spec->val_off, the scale factor is in arg_spec->scale. > + * Firstly, we fetch the base register contents and the index > + * register contents from pt_regs. Secondly, we multiply the > + * index register contents by the scale factor, then add the > + * base address and the offset to get the final address. Finally, > + * we do another user-space probe read to fetch argument value > + * itself. > + */ > + err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off); > + if (err) > + return err; > + err = bpf_probe_read_kernel(&idx, sizeof(idx), (void *)ctx + arg_spec->idx_reg_off); > + if (err) > + return err; > + err = bpf_probe_read_user(&val, sizeof(val), > + (void *)val + idx * arg_spec->scale + arg_spec->val_off); > + if (err) > + return err; > +#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ > + val >>= arg_spec->arg_bitshift; > #endif > break; > default: If possible, could you add some tests which actually trigger a usdt pattern like "-1@-96(%rbp,%rax,8)"? There are much more usdt patterns e.g. in https://lore.kernel.org/bpf/b3ce39f0-c52b-4787-980c-973bd4228349@linux.dev/ === with -O2 and with gcc14 on x86: stapsdt 0x00000087 NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt12 Location: 0x000000000000258f, Base: 0x0000000000000000, Semaphore: 0x0000000000000006 Arguments: -4@$2 -4@$3 -8@$42 -8@$44 -4@$5 -8@$6 8@%rdx 8@%rsi -4@$-9 -2@%cx -2@nums(%rax,%rax) -1@t1+4(%rip) ... === But we didn't add those '-2@nums(%rax,%rax)' '-1@t1+4(%rip)' as they are very rare. > diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c > index 4e4a52742b01..260211e896d5 100644 > --- a/tools/lib/bpf/usdt.c > +++ b/tools/lib/bpf/usdt.c > @@ -200,6 +200,7 @@ enum usdt_arg_type { > USDT_ARG_CONST, > USDT_ARG_REG, > USDT_ARG_REG_DEREF, > + USDT_ARG_SIB, > }; > > /* should match exactly struct __bpf_usdt_arg_spec from usdt.bpf.h */ > @@ -207,6 +208,8 @@ struct usdt_arg_spec { > __u64 val_off; > enum usdt_arg_type arg_type; > short reg_off; > + short idx_reg_off; > + short scale; > bool arg_signed; > char arg_bitshift; > }; > @@ -1283,11 +1286,28 @@ static int calc_pt_regs_off(const char *reg_name) > > static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg, int *arg_sz) > { > - char reg_name[16]; > - int len, reg_off; > + char reg_name[16], idx_reg_off, idx_reg_name[16]; > + int len, reg_off, scale; > long off; > > - if (sscanf(arg_str, " %d @ %ld ( %%%15[^)] ) %n", arg_sz, &off, reg_name, &len) == 3) { > + if (sscanf(arg_str, " %d @ %ld ( %%%15[^,] , %%%15[^,] , %d ) %n", > + arg_sz, &off, reg_name, idx_reg_name, &scale, &len) == 5) { > + /* Scale Index Base case, e.g., 1@-96(%rbp,%rax,8)*/ > + arg->arg_type = USDT_ARG_SIB; > + arg->val_off = off; > + arg->scale = scale; > + > + reg_off = calc_pt_regs_off(reg_name); > + if (reg_off < 0) > + return reg_off; > + arg->reg_off = reg_off; > + > + idx_reg_off = calc_pt_regs_off(idx_reg_name); > + if (idx_reg_off < 0) > + return idx_reg_off; > + arg->idx_reg_off = idx_reg_off; > + } else if (sscanf(arg_str, " %d @ %ld ( %%%15[^)] ) %n", > + arg_sz, &off, reg_name, &len) == 3) { > /* Memory dereference case, e.g., -4@-20(%rbp) */ > arg->arg_type = USDT_ARG_REG_DEREF; > arg->val_off = off;