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riscv, bpf: Remap BPF_REG_0 and RV_REG_TCC

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To prepare for supporting bpf stack arguments and unifying the calling
convention between bpf2bpf calls and kfunc calls, remap BPF_REG_0 to t6
and RV_REG_TCC to t5.

In the riscv abi, a0-a7 are designated for function argument passing.
Freeing a5 and a6 allows bpf2bpf calls to pass extra arguments (6th to
8th) via a5-a7 consistently with kfuncs.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/bpf/20260905085857.14143-2-pulehui@huaweicloud.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Pu Lehui 2026-09-05 08:58:55 +00:00 committed by Kumar Kartikeya Dwivedi
parent 3ccdb07813
commit f80a09c486
No known key found for this signature in database
GPG Key ID: 472D377B63542F83
4 changed files with 13 additions and 13 deletions
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10
arch/riscv/net/bpf_jit_comp64.c
View File

@ -23,11 +23,11 @@
/* fentry and TCC init insns will be skipped on tailcall */
#define RV_TAILCALL_OFFSET ((RV_FENTRY_NINSNS + 1) * 4)
#define RV_REG_TCC RV_REG_A6
#define RV_REG_TCC RV_REG_T5
#define RV_REG_ARENA RV_REG_S7 /* For storing arena_vm_start */
static const int regmap[] = {
[BPF_REG_0] = RV_REG_A5,
[BPF_REG_0] = RV_REG_T6,
[BPF_REG_1] = RV_REG_A0,
[BPF_REG_2] = RV_REG_A1,
[BPF_REG_3] = RV_REG_A2,
@ -47,13 +47,13 @@ static const int pt_regmap[] = {
[RV_REG_A2] = offsetof(struct pt_regs, a2),
[RV_REG_A3] = offsetof(struct pt_regs, a3),
[RV_REG_A4] = offsetof(struct pt_regs, a4),
[RV_REG_A5] = offsetof(struct pt_regs, a5),
[RV_REG_S1] = offsetof(struct pt_regs, s1),
[RV_REG_S2] = offsetof(struct pt_regs, s2),
[RV_REG_S3] = offsetof(struct pt_regs, s3),
[RV_REG_S4] = offsetof(struct pt_regs, s4),
[RV_REG_S5] = offsetof(struct pt_regs, s5),
[RV_REG_T0] = offsetof(struct pt_regs, t0),
[RV_REG_T6] = offsetof(struct pt_regs, t6),
};
enum {
@ -239,7 +239,7 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
emit_addi(RV_REG_SP, RV_REG_SP, stack_adjust, ctx);
/* Set return value. */
if (!is_tail_call)
emit_addiw(RV_REG_A0, RV_REG_A5, 0, ctx);
emit_addiw(RV_REG_A0, regmap[BPF_REG_0], 0, ctx);
emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
is_tail_call ? RV_TAILCALL_OFFSET : 0, ctx);
}
@ -1075,7 +1075,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
if (save_ret)
stack_size += 16; /* Save both A5 (BPF R0) and A0 */
stack_size += 16; /* Save both RV_REG_T6 (BPF R0) and RV_REG_A0 */
retval_off = stack_size;
stack_size += nr_arg_slots * 8;

8
arch/riscv/net/bpf_timed_may_goto.S
View File

@ -10,7 +10,7 @@
* - 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
* ptr = BPF_REG_FP (s5) + BPF_REG_AX (t0). BPF R0-R5 (t6, a0-a4) are saved
* across the call; BPF_REG_FP (s5) is callee-saved and needs no saving.
*/
@ -20,8 +20,8 @@ SYM_FUNC_START(arch_bpf_timed_may_goto)
REG_S s0, 6*SZREG(sp)
addi s0, sp, 8*SZREG
/* Save BPF registers R0-R5 (a5, a0-a4) */
REG_S a5, 5*SZREG(sp)
/* Save BPF registers R0-R5 (t6, a0-a4) */
REG_S t6, 5*SZREG(sp)
REG_S a0, 4*SZREG(sp)
REG_S a1, 3*SZREG(sp)
REG_S a2, 2*SZREG(sp)
@ -38,7 +38,7 @@ SYM_FUNC_START(arch_bpf_timed_may_goto)
REG_L a2, 2*SZREG(sp)
REG_L a1, 3*SZREG(sp)
REG_L a0, 4*SZREG(sp)
REG_L a5, 5*SZREG(sp)
REG_L t6, 5*SZREG(sp)
REG_L s0, 6*SZREG(sp)
REG_L ra, 7*SZREG(sp)

2
tools/testing/selftests/bpf/progs/verifier_jit_inline.c
View File

@ -11,7 +11,7 @@ __jited(" addq %gs:{{.*}}, %rax")
__arch_arm64
__jited(" mrs x8, SP_EL0")
__arch_riscv64
__jited(" mv a5, tp")
__jited(" mv t6, tp")
__arch_loongarch
__jited(" move $a5, $tp")
int inline_bpf_get_current_task(void)

6
tools/testing/selftests/bpf/progs/verifier_ldsx.c
View File

@ -289,11 +289,11 @@ __jited("ldrsh x22, [x11, #0x18]")
__jited("add x11, x0, x28")
__jited("ldrsb x22, [x11, #0x20]")
__arch_riscv64
__jited("add t2, a5, s7")
__jited("add t2, t6, s7")
__jited("lw s3, 0x10(t2)")
__jited("add t2, a5, s7")
__jited("add t2, t6, s7")
__jited("lh s3, 0x18(t2)")
__jited("add t2, a5, s7")
__jited("add t2, t6, s7")
__jited("lb s3, 0x20(t2)")
__jited("add t2, a0, s7")
__jited("lw s4, 0x10(t2)")