powerpc64/bpf: Moving tail_call_cnt to bottom of frame

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To support tailcalls in subprogs, tail_call_cnt needs to be on the BPF
trampoline stack frame. In a regular BPF program or subprog stack
frame, the position of tail_call_cnt is after the NVR save area
(BPF_PPC_STACK_SAVE). To avoid complex logic in deducing offset for
tail_call_cnt, it has to be kept at the same offset on the trampoline
frame as well. But doing that wastes nearly all of BPF_PPC_STACK_SAVE
bytes on the BPF trampoline stack frame as the NVR save area is not
the same for BPF trampoline and regular BPF programs. Address this by
moving tail_call_cnt to the bottom of the frame.

This change avoids the need to account for BPF_PPC_STACK_SAVE bytes
in the BPF trampoline stack frame when support for tailcalls in BPF
subprogs is added later. Also, this change makes offset calculation
of tail_call_cnt field simpler all across.

Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260124075223.6033-2-adubey@linux.ibm.com

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This commit is contained in:

Abhishek Dubey 2026-01-24 13:22:18 +05:30 • committed by Madhavan Srinivasan

parent 815a8d2feb

commit 15513beeb6

3 changed files with 24 additions and 14 deletions

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1

arch/powerpc/net/bpf_jit.h

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6

arch/powerpc/net/bpf_jit_comp.c

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31

arch/powerpc/net/bpf_jit_comp64.c

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