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Wed, 26 Nov 2025 00:29:54 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 26 Nov 2025 09:29:52 +0100 To: Andrii Nakryiko Cc: Andrii Nakryiko , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Song Liu , Yonghong Song , John Fastabend Subject: Re: [PATCH bpf-next 2/4] libbpf: Add uprobe syscall feature detection Message-ID: References: <20251117083551.517393-1-jolsa@kernel.org> <20251117083551.517393-3-jolsa@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Nov 24, 2025 at 09:29:05AM -0800, Andrii Nakryiko wrote: > On Mon, Nov 17, 2025 at 12:36 AM Jiri Olsa wrote: > > > > Adding uprobe syscall feature detection that will be used > > in following changes. > > > > Signed-off-by: Jiri Olsa > > --- > > tools/lib/bpf/features.c | 22 ++++++++++++++++++++++ > > tools/lib/bpf/libbpf_internal.h | 2 ++ > > 2 files changed, 24 insertions(+) > > > > diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c > > index b842b83e2480..587571c21d2d 100644 > > --- a/tools/lib/bpf/features.c > > +++ b/tools/lib/bpf/features.c > > @@ -506,6 +506,25 @@ static int probe_kern_arg_ctx_tag(int token_fd) > > return probe_fd(prog_fd); > > } > > > > +#ifdef __x86_64__ > > nit: , give the code a bit of breathing room :) ok :) > > +#ifndef __NR_uprobe > > +#define __NR_uprobe 336 > > +#endif > > > > > +static int probe_uprobe_syscall(int token_fd) > > +{ > > + /* > > + * When not executed from executed kernel provided trampoline, > > "executed from executed kernel"? Maybe: "If kernel supports uprobe() > syscall, it will return -ENXIO when called from the outside of a > kernel-generated uprobe trampoline."? Otherwise it will be -ENOSYS or > something like this, right? ugh, yep > > > + * the uprobe syscall returns ENXIO error. > > + */ > > + return syscall(__NR_uprobe) == -1 && errno == ENXIO; > > nit: please use < 0 check for consistency with other error checking > logic everywhere else ok thanks, jirka > > > > +} > > +#else > > +static int probe_uprobe_syscall(int token_fd) > > +{ > > + return 0; > > +} > > +#endif > > + > > typedef int (*feature_probe_fn)(int /* token_fd */); > > > > static struct kern_feature_cache feature_cache; > > @@ -581,6 +600,9 @@ static struct kern_feature_desc { > > [FEAT_BTF_QMARK_DATASEC] = { > > "BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec, > > }, > > + [FEAT_UPROBE_SYSCALL] = { > > + "Kernel supports uprobe syscall", probe_uprobe_syscall, > > + }, > > }; > > > > bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id) > > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h > > index fc59b21b51b5..69aa61c038a9 100644 > > --- a/tools/lib/bpf/libbpf_internal.h > > +++ b/tools/lib/bpf/libbpf_internal.h > > @@ -392,6 +392,8 @@ enum kern_feature_id { > > FEAT_ARG_CTX_TAG, > > /* Kernel supports '?' at the front of datasec names */ > > FEAT_BTF_QMARK_DATASEC, > > + /* Kernel supports uprobe syscall */ > > + FEAT_UPROBE_SYSCALL, > > __FEAT_CNT, > > }; > > > > -- > > 2.51.1 > >