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[45.79.69.94]) by smtp.gmail.com with ESMTPSA id 17sm2843733pfo.4.2018.04.27.03.03.09 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 27 Apr 2018 03:03:12 -0700 (PDT) From: Leo Yan To: Alexei Starovoitov , Daniel Borkmann , "David S. Miller" , Jonathan Corbet , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: Leo Yan Subject: [PATCH bpf-next v2] bpf, doc: Update bpf_jit_enable limitation for CONFIG_BPF_JIT_ALWAYS_ON Date: Fri, 27 Apr 2018 18:02:54 +0800 Message-Id: <1524823374-6174-1-git-send-email-leo.yan@linaro.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When CONFIG_BPF_JIT_ALWAYS_ON is enabled, kernel has limitation for bpf_jit_enable, so it has fixed value 1 and we cannot set it to 2 for JIT opcode dumping; this patch is to update the doc for it. Suggested-by: Daniel Borkmann Signed-off-by: Leo Yan --- Documentation/networking/filter.txt | 6 ++++++ 1 file changed, 6 insertions(+) -- 1.9.1 diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt index fd55c7d..5032e12 100644 --- a/Documentation/networking/filter.txt +++ b/Documentation/networking/filter.txt @@ -483,6 +483,12 @@ Example output from dmesg: [ 3389.935851] JIT code: 00000030: 00 e8 28 94 ff e0 83 f8 01 75 07 b8 ff ff 00 00 [ 3389.935852] JIT code: 00000040: eb 02 31 c0 c9 c3 +When CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set to 1 and +setting any other value than that will return in failure. This is even the case for +setting bpf_jit_enable to 2, since dumping the final JIT image into the kernel log +is discouraged and introspection through bpftool (under tools/bpf/bpftool/) is the +generally recommended approach instead. + In the kernel source tree under tools/bpf/, there's bpf_jit_disasm for generating disassembly out of the kernel log's hexdump: