Commit b9fe8e8d authored by Dave Thaler's avatar Dave Thaler Committed by Alexei Starovoitov
Browse files

bpf, docs: Add signed comparison example 



Improve clarity by adding an example of a signed comparison instruction

Signed-off-by: default avatarDave Thaler <dthaler@microsoft.com>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20230310233814.4641-1-dthaler1968@googlemail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent ab4c15fe

Documentation/bpf/instruction-set.rst

+10 −1
Original line number Diff line number Diff line
@@ -11,7 +11,8 @@ Documentation conventions 
=========================



For brevity, this document uses the type notion "u64", "u32", etc.

to mean an unsigned integer whose width is the specified number of bits.

to mean an unsigned integer whose width is the specified number of bits,

and "s32", etc. to mean a signed integer of the specified number of bits.



Registers and calling convention

================================
@@ -264,6 +265,14 @@ 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.



Example:



``BPF_JSGE | BPF_X | BPF_JMP32`` (0x7e) means::



  if (s32)dst s>= (s32)src goto +offset



where 's>=' indicates a signed '>=' comparison.



Helper functions

~~~~~~~~~~~~~~~~