From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 34F08337BAD; Fri, 20 Feb 2026 10:42:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771584178; cv=none; b=KdQ2sP9+UsQg1F5m9uAVJ6uGJmoZJ8sXM4fJu6ziMLxGggDI3NwqZMN1MsC2HheMx6g3T2H+iDtrCU5AY/lOvfI/A11wGQw7dJ1bKHdq0JkBysFfqUKxzLYLH3Y+HPrj6FULr1sW7PkjsGZbTYvgI/t4G/eLsUPsirdYqdMLYXY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771584178; c=relaxed/simple; bh=T01UZTS7Rh6lX2vUBu1yk7ioVwV3kY+g3pgCsKy39j8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=n/P/wNKp3q6OEivEkoC5dH+RbdrFXmTTubsixyYXPx5dGOJ2q2RBwyDXC+9W2n5XWsIf6t530qO/RI529NQCgGxhwGDOzn8az+2DSdXXET6aA48dAup/5MaJGGLdKx57t6x7gvmdmQZqBBo8Fj/mq/Fj99Rr3qOxuuLwtE4W3lc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=q3w0d0bn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="q3w0d0bn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C409AC116C6; Fri, 20 Feb 2026 10:42:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771584177; bh=T01UZTS7Rh6lX2vUBu1yk7ioVwV3kY+g3pgCsKy39j8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=q3w0d0bniDRWarDHw0EkOjBbnTNAoq1yDLjxHx6NB5v/mzdxN56W84SPeEDRqG935 UuaLpElMBVzESwXyu5Wjq0KfFd/c5uX8EcgXspe8i2lx3qnvaZcLlaN1PqY2LVLBJU xupqSfVgcDhZhuxChUl331NzWsowK5reomPjgln6iQhsZBxLwh2SXoVu5lKkfILXTa 8Zi25l1rbp+B4QJrD9TO+yorX8QtJPQnmPFldkEqR9dF1e1G2HCQUZYWGSQeIV1SXV oyYNXUUcp2zH0LfZo79FKzGjnDiP7mn8skZd4tG7PiYuWveDM8ht28qq7vjpcX2Z+W 4PVmDKbHSVXwg== From: Jiri Olsa To: Andrii Nakryiko Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Song Liu , Yonghong Song , John Fastabend Subject: [PATCHv4 bpf-next 2/5] libbpf: Add support to detect nop,nop5 instructions combo for usdt probe Date: Fri, 20 Feb 2026 11:42:17 +0100 Message-ID: <20260220104220.634154-3-jolsa@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260220104220.634154-1-jolsa@kernel.org> References: <20260220104220.634154-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Adding support to detect nop,nop5 instructions combo for usdt probe by checking on probe's following nop5 instruction. When the nop,nop5 combo is detected together with uprobe syscall, we can place the probe on top of nop5 and get it optimized. Signed-off-by: Jiri Olsa --- tools/lib/bpf/usdt.c | 47 ++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 43 insertions(+), 4 deletions(-) diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c index d1524f6f54ae..c81e0a58caf5 100644 --- a/tools/lib/bpf/usdt.c +++ b/tools/lib/bpf/usdt.c @@ -262,6 +262,7 @@ struct usdt_manager { bool has_bpf_cookie; bool has_sema_refcnt; bool has_uprobe_multi; + bool has_uprobe_syscall; }; struct usdt_manager *usdt_manager_new(struct bpf_object *obj) @@ -301,6 +302,13 @@ struct usdt_manager *usdt_manager_new(struct bpf_object *obj) * usdt probes. */ man->has_uprobe_multi = kernel_supports(obj, FEAT_UPROBE_MULTI_LINK); + + /* + * Detect kernel support for uprobe() syscall, it's presence means we can + * take advantage of faster nop5 uprobe handling. + * Added in: 56101b69c919 ("uprobes/x86: Add uprobe syscall to speed up uprobe") + */ + man->has_uprobe_syscall = kernel_supports(obj, FEAT_UPROBE_SYSCALL); return man; } @@ -585,13 +593,34 @@ static int parse_usdt_note(GElf_Nhdr *nhdr, const char *data, size_t name_off, static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note *note, __u64 usdt_cookie); -static int collect_usdt_targets(struct usdt_manager *man, Elf *elf, const char *path, pid_t pid, - const char *usdt_provider, const char *usdt_name, __u64 usdt_cookie, - struct usdt_target **out_targets, size_t *out_target_cnt) +#if defined(__x86_64__) +static bool has_nop_combo(int fd, long off) +{ + static unsigned char nop_combo[6] = { + 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x00 /* nop,nop5 */ + }; + unsigned char buf[6] = {}; + + if (pread(fd, buf, 6, off) != 6) + return false; + return memcmp(buf, nop_combo, 6) == 0; +} +#else +static bool has_nop_combo(int fd, long off) +{ + return false; +} +#endif + +static int collect_usdt_targets(struct usdt_manager *man, struct elf_fd *elf_fd, const char *path, + pid_t pid, const char *usdt_provider, const char *usdt_name, + __u64 usdt_cookie, struct usdt_target **out_targets, + size_t *out_target_cnt) { size_t off, name_off, desc_off, seg_cnt = 0, vma_seg_cnt = 0, target_cnt = 0; struct elf_seg *segs = NULL, *vma_segs = NULL; struct usdt_target *targets = NULL, *target; + Elf *elf = elf_fd->elf; long base_addr = 0; Elf_Scn *notes_scn, *base_scn; GElf_Shdr base_shdr, notes_shdr; @@ -784,6 +813,16 @@ static int collect_usdt_targets(struct usdt_manager *man, Elf *elf, const char * target = &targets[target_cnt]; memset(target, 0, sizeof(*target)); + /* + * We have uprobe syscall and usdt with nop,nop5 instructions combo, + * so we can place the uprobe directly on nop5 (+1) and get this probe + * optimized. + */ + if (man->has_uprobe_syscall && has_nop_combo(elf_fd->fd, usdt_rel_ip)) { + usdt_abs_ip++; + usdt_rel_ip++; + } + target->abs_ip = usdt_abs_ip; target->rel_ip = usdt_rel_ip; target->sema_off = usdt_sema_off; @@ -998,7 +1037,7 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct /* discover USDT in given binary, optionally limiting * activations to a given PID, if pid > 0 */ - err = collect_usdt_targets(man, elf_fd.elf, path, pid, usdt_provider, usdt_name, + err = collect_usdt_targets(man, &elf_fd, path, pid, usdt_provider, usdt_name, usdt_cookie, &targets, &target_cnt); if (err <= 0) { err = (err == 0) ? -ENOENT : err; -- 2.53.0