Commit 07801a24 authored by Dave Thaler's avatar Dave Thaler Committed by Daniel Borkmann
Browse files

bpf, docs: Clarify PC use in instruction-set.rst 



This patch elaborates on the use of PC by expanding the PC acronym,
explaining the units, and the relative position to which the offset
applies.

Signed-off-by: default avatarDave Thaler <dthaler1968@googlemail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20240426231126.5130-1-dthaler1968@gmail.com
parent 6e25bcf0

Documentation/bpf/standardization/instruction-set.rst

+6 −0
Original line number Diff line number Diff line
@@ -469,6 +469,12 @@ JSLT 0xc any PC += offset if dst < src signed 
JSLE      0xd    any      PC += offset if dst <= src         signed

========  =====  =======  =================================  ===================================================



where 'PC' denotes the program counter, and the offset to increment by

is in units of 64-bit instructions relative to the instruction following

the jump instruction.  Thus 'PC += 1' skips execution of the next

instruction if it's a basic instruction or results in undefined behavior

if the next instruction is a 128-bit wide instruction.



The BPF program needs to store the return value into register R0 before doing an

``EXIT``.