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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: Dave Thaler <dthaler1968@googlemail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20240426231126.5130-1-dthaler1968@gmail.com
This commit is contained in:
Dave Thaler 2024-04-26 16:11:26 -07:00 committed by Daniel Borkmann
parent 6e25bcf06a
commit 07801a24e2
1 changed files with 6 additions and 0 deletions
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6
Documentation/bpf/standardization/instruction-set.rst
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@ -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``.