From: Dave Thaler <dthaler1968=40googlemail.com@dmarc.ietf.org>
To: bpf@vger.kernel.org
Cc: bpf@ietf.org, Dave Thaler <dthaler1968@gmail.com>,
Dave Thaler <dthaler1968@googlemail.com>
Subject: [Bpf] [PATCH bpf-next v3] bpf, docs: Clarify PC use in instruction-set.rst
Date: Fri, 26 Apr 2024 16:11:26 -0700 [thread overview]
Message-ID: <20240426231126.5130-1-dthaler1968@gmail.com> (raw)
Message-ID: <20240426231126.5Nrgl7wL0PDL_Vn6CBeamMTTxuh6vSCoiO-8TqEYfgE@z> (raw)
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.
v1->v2: reword per feedback from Alexei
v2->v3: reword per feedback from David Vernet
Signed-off-by: Dave Thaler <dthaler1968@googlemail.com>
---
Documentation/bpf/standardization/instruction-set.rst | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst
index b44bdacd0..997560aba 100644
--- a/Documentation/bpf/standardization/instruction-set.rst
+++ b/Documentation/bpf/standardization/instruction-set.rst
@@ -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``.
--
2.40.1
--
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next reply other threads:[~2024-04-27 0:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 23:11 Dave Thaler [this message]
2024-04-26 23:11 ` [Bpf] [PATCH bpf-next v3] bpf, docs: Clarify PC use in instruction-set.rst Dave Thaler
2024-04-28 22:01 ` David Vernet
2024-04-28 22:01 ` David Vernet
2024-04-29 10:00 ` patchwork-bot+netdevbpf
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