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Mon, 30 Aug 2021 10:34:42 -0700 (PDT) From: Kumar Kartikeya Dwivedi To: bpf@vger.kernel.org Cc: Kumar Kartikeya Dwivedi , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , Jesper Dangaard Brouer , =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= , netdev@vger.kernel.org Subject: [PATCH bpf-next RFC v1 4/8] libbpf: Resolve invalid kfunc calls with imm = 0, off = 0 Date: Mon, 30 Aug 2021 23:04:20 +0530 Message-Id: <20210830173424.1385796-5-memxor@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210830173424.1385796-1-memxor@gmail.com> References: <20210830173424.1385796-1-memxor@gmail.com> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1874; h=from:subject; bh=0Ipz/Yi43rx5DJpjld7vtB0LLAwruqr1vRK9uMkuMkA=; b=owEBbQKS/ZANAwAIAUzgyIZIvxHKAcsmYgBhLRX9Mu5LQIUGP+W5QKPzu9NrapcpPUMw1aj/KnJT CCXx7P+JAjMEAAEIAB0WIQRLvip+Buz51YI8YRFM4MiGSL8RygUCYS0V/QAKCRBM4MiGSL8Rymu8D/ 93pXwEizs0lNBi2cR5bS+F6hyyOh04qqWu1gJH/5E3zje6haYDJD/B5BQFtRI3dexz0wDfFOEI1H8U w2VPgqyEvdcj9TdNPHKEin/XMCes7aWOIdEDlWu8+C5KSJyZF92lXP4cQhhlwpqOqYfQzgTsNf+URc 6dTfJgNknpTD6MNNp3QJin5Lr5syHl+eKnd+cNoH0sLIovZebJeTSUu+W3Dal2qLfgbPKaIQ0V4LGM GStyxRATNQ5R1HhXXiHI1S8tly0ycLc8FcN3WqutGPbFzrrmvvhUVRFfFXtWpX8K/hlGv+MmNGJg6d LUNzrzPVgKkTfG1Wxp27tVXD54cYHHkhuTtpKAUOJDjSGUddxgcnHWbLkX2i6P8XFcOV8ihscVI7M5 xkY6II67ZEyrKD+RtT9KIl1IfnYS+3/jacWS+ZGEdsMsFAb+UZJ2ME1UJNsptOvKUMSnlOnef1rcNx hRmjG9sanA1BQyZiCZKS7uYn0aIP9FNyIVJDLdY5s87ljedX7wJslkgCb19tOLNBU+E3pc28iotVby /6yT7homc24+naZrza5DB8xrLfmsAjcjACgoNRQcc+ZD1ZQEvfvpXbA/fWgt7Uwxgjb4L0txqNbJZw TRpqwTTj6wnntO6LlixNl5uaofL1I9HJv+pQ5i/prj9H6n9bD4sikJ2kIucg== X-Developer-Key: i=memxor@gmail.com; a=openpgp; fpr=4BBE2A7E06ECF9D5823C61114CE0C88648BF11CA Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Preserve these calls as it allows verifier to succeed in loading the program if they are determined to be unreachable after dead code elimination during program load. If not, the verifier will fail at runtime. Signed-off-by: Kumar Kartikeya Dwivedi --- tools/lib/bpf/libbpf.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index c4677ef97caa..9df90098f111 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -6736,9 +6736,14 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, &kern_btf, &kern_btf_fd); if (kfunc_id < 0) { - pr_warn("extern (func ksym) '%s': not found in kernel BTF\n", + pr_warn("extern (func ksym) '%s': not found in kernel BTF, encoding btf_id as 0\n", ext->name); - return kfunc_id; + /* keep invalid kfuncs, so that verifier can load the program if + * they get removed during DCE pass in the verifier. + * The encoding must be insn->imm = 0, insn->off = 0. + */ + kfunc_id = kern_btf_fd = 0; + goto resolve; } if (kern_btf != obj->btf_vmlinux) { @@ -6798,11 +6803,18 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, return -EINVAL; } +resolve: ext->is_set = true; ext->ksym.kernel_btf_obj_fd = kern_btf_fd; ext->ksym.kernel_btf_id = kfunc_id; - pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n", - ext->name, kfunc_id); + if (kfunc_id) { + pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n", + ext->name, kfunc_id); + } else { + ext->ksym.offset = 0; + pr_debug("extern (func ksym) '%s': added special invalid kfunc with imm = 0\n", + ext->name); + } return 0; } -- 2.33.0