On 10/19, dthaler1968@xxxxxxxxxxxxxx wrote:
From: Dave Thaler <dthaler@xxxxxxxxxxxxx>
Explain helper functions.
Kernel functions and bpf to bpf calls are covered in
a later commit in this set ("Add extended call instructions").
Signed-off-by: Dave Thaler <dthaler@xxxxxxxxxxxxx>
---
Documentation/bpf/instruction-set.rst | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/Documentation/bpf/instruction-set.rst
b/Documentation/bpf/instruction-set.rst
index 29b599c70..f9e56d9d5 100644
--- a/Documentation/bpf/instruction-set.rst
+++ b/Documentation/bpf/instruction-set.rst
@@ -242,7 +242,7 @@ BPF_JSET 0x40 PC += off if dst & src
BPF_JNE 0x50 PC += off if dst != src
BPF_JSGT 0x60 PC += off if dst > src signed
BPF_JSGE 0x70 PC += off if dst >= src signed
-BPF_CALL 0x80 function call
+BPF_CALL 0x80 function call see `Helper functions`_
BPF_EXIT 0x90 function / program return BPF_JMP only
BPF_JLT 0xa0 PC += off if dst < src unsigned
BPF_JLE 0xb0 PC += off if dst <= src unsigned
@@ -253,6 +253,22 @@ BPF_JSLE 0xd0 PC += off if dst <= src signed
The eBPF program needs to store the return value into register R0 before
doing a
BPF_EXIT.
+Helper functions
+~~~~~~~~~~~~~~~~
+Helper functions are a concept whereby BPF programs can call into a
+set of function calls exposed by the eBPF runtime. Each helper
(the series looks good to me, but I'm assuming Alexei will take a look at
these anywey because he did for the previous submissions)
Not really related to the patch, but in general, quoting from the above:
"BPF programs can call ... by the eBPF runtime". I know we do it all the
time
and use BPF/eBPF interchangeably, but should we try to be consistent at
least
within the same page?
$ grep -r 'eBPF program' Documentation/bpf/ | wc -l
34
$ grep -r ' BPF program' Documentation/bpf/ | wc -l
97
+function is identified by an integer used in a ``BPF_CALL`` instruction.
+The available helper functions may differ for each eBPF program type.
+
+Conceptually, each helper function is implemented with a commonly shared
function
+signature defined as:
+
+ u64 function(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+
+In actuality, each helper function is defined as taking between 0 and 5
arguments,
+with the remaining registers being ignored. The definition of a helper
function
+is responsible for specifying the type (e.g., integer, pointer, etc.) of
the value returned,
+the number of arguments, and the type of each argument.
Load and store instructions
===========================
--
2.33.4
