[PATCH bpf-next v3 0/4] bpf, riscv: Add support for indirect jumps

[Chen Pei]

The indirect jump instruction (BPF_JMP | BPF_JA | BPF_X, "gotox") and the
BPF_MAP_TYPE_INSN_ARRAY jump tables it consumes are core features: the
verifier accepts them on every architecture, and the x86-64, arm64 and
powerpc JITs implement them. On riscv64 a program using gotox passes
verification and then fails to load, because the JIT does not know the
opcode and CONFIG_BPF_JIT_ALWAYS_ON leaves no interpreter to fall back
onto.

This series adds the riscv64 support and turns the existing selftests on
for that architecture.

Patch 1 emits "jalr zero, rd, 0" for gotox and publishes the xlated to
jitted offsets through bpf_prog_update_insn_ptrs(), which is what fills
in the jump table addresses. Patches 2 to 4 widen the arch guards in
verifier_gotox.c, compute_live_registers.c and bpf_insn_array.c to
riscv64, the same way the other architectures were enabled.

Changes since v2:
- Pick up Pu Lehui's Reviewed-by on patch 1.
- Enable two more gotox test files for riscv64: compute_live_registers.c
  and bpf_insn_array.c.

Changes since v1:
- Rebased onto bpf-next.
- Patch 1: reword the code comment to say "shift ctx->offset[] by one".
- Patch 2: collapse the multi-line #endif marker to a single line.
- Added Reviewed-by/Acked-by from Björn Töpel.

Testing
=======

Environment: QEMU virt rv64, with CONFIG_BPF_JIT=y,
CONFIG_BPF_JIT_ALWAYS_ON=y, CONFIG_DEBUG_INFO_BTF=y; selftests
cross-built with clang 23.

- test_progs -t verifier_gotox: 33/33 subtests pass.
- test_progs -t bpf_insn_array: 20/20 subtests pass.
- test_progs -t compute_live_registers: 20/20 subtests pass, including
  the gotox liveness subtest.
- test_progs-cpuv4 -t bpf_gotox: 14/14 subtests pass.

Chen Pei (4):
  bpf, riscv: Add support for indirect jumps
  selftests/bpf: Enable gotox tests for riscv64
  selftests/bpf: Enable gotox liveness test for riscv64
  selftests/bpf: Enable instruction array test for riscv64

 arch/riscv/net/bpf_jit_comp64.c                  |  5 +++++
 arch/riscv/net/bpf_jit_core.c                    | 16 ++++++++++++++--
 .../selftests/bpf/prog_tests/bpf_insn_array.c    |  3 ++-
 .../selftests/bpf/progs/compute_live_registers.c |  5 +++--
 .../testing/selftests/bpf/progs/verifier_gotox.c |  6 ++++--
 5 files changed, 28 insertions(+), 7 deletions(-)

-- 
2.50.1