[PATCH bpf-next v2 0/2] 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. Patch 2 widens the arch guard in
verifier_gotox.c to riscv64, the same way arm64 and powerpc were enabled.

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 22.

- test_progs -t verifier_gotox: 27/27 subtests pass on bpf-next, 13 of
  them executed through BPF_PROG_TEST_RUN.
- test_progs-cpuv4 -t bpf_gotox: 14/14 subtests pass, none skipped.
  The cpuv4 flavor is needed here because bpf_gotox gates its subtests
  on __BPF_FEATURE_GOTOX, which clang only defines for -mcpu=v4.

Chen Pei (2):
  bpf, riscv: Add support for indirect jumps
  selftests/bpf: Enable gotox tests for riscv64

 arch/riscv/net/bpf_jit_comp64.c                  |  5 +++++
 arch/riscv/net/bpf_jit_core.c                    | 16 ++++++++++++++--
 .../testing/selftests/bpf/progs/verifier_gotox.c |  6 ++++--
 3 files changed, 23 insertions(+), 4 deletions(-)

-- 
2.50.1