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authorLeo Yan <leo.yan@linaro.org>2018-04-27 18:02:54 +0800
committerDaniel Borkmann <daniel@iogearbox.net>2018-04-27 12:08:13 +0200
commit2c25fc9a503adef4279951382fc9d47b59977f59 (patch)
tree074932b6ced2f62bc8df04454ab59fd456e8ded1
parentMerge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next (diff)
downloadlinux-dev-2c25fc9a503adef4279951382fc9d47b59977f59.tar.xz
linux-dev-2c25fc9a503adef4279951382fc9d47b59977f59.zip
bpf, doc: Update bpf_jit_enable limitation for CONFIG_BPF_JIT_ALWAYS_ON
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 <daniel@iogearbox.net> Signed-off-by: Leo Yan <leo.yan@linaro.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
-rw-r--r--Documentation/networking/filter.txt6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index fd55c7de9991..5032e1263bc9 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: