On 2026/7/22 12:21, Feng Jiang wrote:
Implement arch_bpf_timed_may_goto() for the RV64 JIT. The argument and
return value are carried in BPF_REG_AX, and BPF R0-R5 are preserved
across the call to the generic bpf_check_timed_may_goto().
Enable bpf_jit_supports_timed_may_goto() so the verifier uses the timed
expansion path.
Signed-off-by: Feng Jiang <[email protected]>
---
arch/riscv/net/Makefile | 2 +-
arch/riscv/net/bpf_jit_comp64.c | 12 +++++++++-
arch/riscv/net/bpf_timed_may_goto.S | 47 +++++++++++++++++++++++++++++++++++++
3 files changed, 59 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/net/Makefile b/arch/riscv/net/Makefile
index 9a1e5f0a94e5..6458d4d51990 100644
--- a/arch/riscv/net/Makefile
+++ b/arch/riscv/net/Makefile
@@ -3,7 +3,7 @@
obj-$(CONFIG_BPF_JIT) += bpf_jit_core.o
ifeq ($(CONFIG_ARCH_RV64I),y)
- obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o
+ obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o bpf_timed_may_goto.o
else
obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o
endif
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index ad089a9a4ea9..8fe8969fb8a0 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -1841,7 +1841,12 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn,
struct rv_jit_context *ctx,
if (aux->tail_call_reachable && insn->src_reg ==
BPF_PSEUDO_CALL)
emit_sd(RV_REG_SP, ctx->tcc_offset, RV_REG_TCC, ctx);
- if (insn->src_reg != BPF_PSEUDO_CALL)
+ /*
+ * arch_bpf_timed_may_goto() is emitted by the verifier and
+ * returns its result in BPF_REG_AX instead of BPF_REG_0, so
+ * skip the normal "move return register into R0".
+ */
+ if (insn->src_reg != BPF_PSEUDO_CALL && addr !=
(u64)arch_bpf_timed_may_goto)
emit_mv(bpf_to_rv_reg(BPF_REG_0, ctx), RV_REG_A0, ctx);
break;
}
@@ -2161,3 +2166,8 @@ bool bpf_jit_supports_subprog_tailcalls(void)
{
return true;
}
+
+bool bpf_jit_supports_timed_may_goto(void)
+{
+ return true;
+}
diff --git a/arch/riscv/net/bpf_timed_may_goto.S
b/arch/riscv/net/bpf_timed_may_goto.S
new file mode 100644
index 000000000000..f4bf2cd10586
--- /dev/null
+++ b/arch/riscv/net/bpf_timed_may_goto.S
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2026 Feng Jiang <[email protected]> */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+
+/*
+ * Trampoline for the BPF timed may_goto loop bound. Custom calling convention:
+ * - input: stack offset in BPF_REG_AX (t0)
+ * - output: updated count in BPF_REG_AX (t0)
+ *
+ * Calls bpf_check_timed_may_goto(ptr) with the standard RISC-V ABI, where
+ * ptr = BPF_REG_FP (s5) + BPF_REG_AX (t0). BPF R0-R5 (a5, a0-a4) are saved
+ * across the call; BPF_REG_FP (s5) is callee-saved and needs no saving.
+ */
+
+SYM_FUNC_START(arch_bpf_timed_may_goto)
+ addi sp, sp, -64
+ sd ra, 56(sp)
+ sd s0, 48(sp)
+ addi s0, sp, 64
+
+ /* Save BPF registers R0-R5 (a5, a0-a4) */
+ sd a5, 40(sp)
+ sd a0, 32(sp)
+ sd a1, 24(sp)
+ sd a2, 16(sp)
+ sd a3, 8(sp)
+ sd a4, 0(sp)
+
+ add a0, t0, s5
+ call bpf_check_timed_may_goto
+ mv t0, a0
+
+ /* Restore BPF registers R0-R5 */
+ ld a4, 0(sp)
+ ld a3, 8(sp)
+ ld a2, 16(sp)
+ ld a1, 24(sp)
+ ld a0, 32(sp)
+ ld a5, 40(sp)
+
+ ld s0, 48(sp)
+ ld ra, 56(sp)
+ addi sp, sp, 64
+ ret
+SYM_FUNC_END(arch_bpf_timed_may_goto)
I think we should use REG_S/REG_L/SZREG like in arch/riscv ([0]) – it
keeps us in sync with upstream and will make it easier if we may later
port timed_may_goto to RV32.
[0] arch/riscv/kernel/mcount.S
