From nobody Thu Apr 2 15:36:14 2026 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 A923619EEC2; Tue, 10 Feb 2026 13:37:17 +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=1770730637; cv=none; b=pGQFSW5uEk2XyyRdOW+ycby2Y7vR1ek743H9eRLZ0zES9QiFyFFn7wLRm+JzP47g9mINCVvH6l2SbLQXKr6fqHh1GdURmve+W5Movp3Uy4u2ZnmmeUa+EKiahrJTqJ4EjflNHjzT3ZYt6+ecgUPW0j+8OMNRlusNwM9vFXfDDAM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770730637; c=relaxed/simple; bh=/e5FLaITB6aTJI/Ft1Jn5QjDQwpwtZrhk8oW4a8Zxes=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Qhk+/iLVsDAalHHUZ00rBGUjkeq767umCOIFuQFiOMhBCAXqOxpLzGyiD+8EI8rWeKmtEFYfrgVIWEJHgP/mZ4RmdKyYq1EH4ZcfYQDBotLrV3wRFeoeJ4Ns34S9YOuNCL7jte5FJsemIdUim/NQixqPQtIK5BFDerwlYCdet38= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cCAuXSYe; 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="cCAuXSYe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73FEAC19423; Tue, 10 Feb 2026 13:37:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770730637; bh=/e5FLaITB6aTJI/Ft1Jn5QjDQwpwtZrhk8oW4a8Zxes=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cCAuXSYelOTYd3HF6We1IHZdPb5TxjroPvpNdZ0VFtu92yYDVF9Vvpt4I4KxPUIC8 ZIVrmVXIjNXqvM3nuqAfSHHcNN3x43Ct4cWB5nb9u+3ZsLw4vKPXhPYH5MftV3vZnl PMClYGnhBXlnw4LjNATKWXuiu8FAGJYSV+jhwRmuUrnRQyWrkfJ5+iy6bdVNk0OclH JJiwIUMFBFK4BL3hg3reqpdASO3Cc33ZxFRWEQAkbEk0Kpnh35B8J8nZ5wdJGH5Ifz 8eGgXyPfbv10xIj6T1JcSFNQb7Qz5g3x1blwq3l/i0iKuYOc0gIP/moWqHhyA0Ku8T CzW/kQ6z2aJTQ== From: Jiri Olsa To: Andrii Nakryiko Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Song Liu , Yonghong Song , John Fastabend Subject: [PATCHv2 bpf-next 2/5] libbpf: Add support to detect nop,nop5 instructions combo for usdt probe Date: Tue, 10 Feb 2026 14:36:46 +0100 Message-ID: <20260210133649.524292-3-jolsa@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260210133649.524292-1-jolsa@kernel.org> References: <20260210133649.524292-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. [1] https://github.com/libbpf/usdt Signed-off-by: Jiri Olsa --- tools/lib/bpf/usdt.c | 55 ++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 51 insertions(+), 4 deletions(-) diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c index d1524f6f54ae..4e5f70bb4c31 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; }; =20 struct usdt_manager *usdt_manager_new(struct bpf_object *obj) @@ -301,6 +302,13 @@ struct usdt_manager *usdt_manager_new(struct bpf_objec= t *obj) * usdt probes. */ man->has_uprobe_multi =3D 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 u= probe") + */ + man->has_uprobe_syscall =3D kernel_supports(obj, FEAT_UPROBE_SYSCALL); return man; } =20 @@ -585,13 +593,42 @@ static int parse_usdt_note(GElf_Nhdr *nhdr, const cha= r *data, size_t name_off, =20 static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note = *note, __u64 usdt_cookie); =20 -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] =3D { + 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x00 /* nop,nop5 */ + }; + unsigned char buf[6] =3D {}; + + /* + * We are using file descriptor that backs Elf object, + * let's dup it to be on the safe side. + */ + fd =3D dup(fd); + if (fd < 0) + return false; + if (lseek(fd, off, SEEK_SET) =3D=3D off) + read(fd, buf, 6); + close(fd); + return memcmp(buf, nop_combo, 6) =3D=3D 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 *e= lf_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 =3D 0, vma_seg_cnt =3D 0, target_= cnt =3D 0; struct elf_seg *segs =3D NULL, *vma_segs =3D NULL; struct usdt_target *targets =3D NULL, *target; + Elf *elf =3D elf_fd->elf; long base_addr =3D 0; Elf_Scn *notes_scn, *base_scn; GElf_Shdr base_shdr, notes_shdr; @@ -784,6 +821,16 @@ static int collect_usdt_targets(struct usdt_manager *m= an, Elf *elf, const char * target =3D &targets[target_cnt]; memset(target, 0, sizeof(*target)); =20 + /* + * 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 =3D usdt_abs_ip; target->rel_ip =3D usdt_rel_ip; target->sema_off =3D usdt_sema_off; @@ -998,7 +1045,7 @@ 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 =3D collect_usdt_targets(man, elf_fd.elf, path, pid, usdt_provider, u= sdt_name, + err =3D collect_usdt_targets(man, &elf_fd, path, pid, usdt_provider, usdt= _name, usdt_cookie, &targets, &target_cnt); if (err <=3D 0) { err =3D (err =3D=3D 0) ? -ENOENT : err; --=20 2.53.0