From 68e5627579d788d9e992cc06a69760f20b6841d6 Mon Sep 17 00:00:00 2001 From: Puranjay Mohan Date: Tue, 12 May 2026 21:51:53 -0700 Subject: [PATCH] bpf, arm64: Map BPF_REG_0 to x8 instead of x7 Move the BPF return value register from x7 to x8, freeing x7 for use as an argument register. AAPCS64 designates x8 as the indirect result location register; it is caller-saved and not used for argument passing, making it a suitable home for BPF_REG_0. This is a prerequisite for stack argument support, which needs x5-x7 to pass arguments 6-8 to native kfuncs following the AAPCS64 calling convention. Signed-off-by: Puranjay Mohan Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20260513045153.2402197-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov --- arch/arm64/net/bpf_jit_comp.c | 4 ++-- arch/arm64/net/bpf_timed_may_goto.S | 8 ++++---- .../testing/selftests/bpf/progs/verifier_jit_inline.c | 2 +- tools/testing/selftests/bpf/progs/verifier_ldsx.c | 6 +++--- .../selftests/bpf/progs/verifier_private_stack.c | 10 +++++----- 5 files changed, 15 insertions(+), 15 deletions(-) diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 0816c40fc7af..085e650662e3 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -47,7 +47,7 @@ /* Map BPF registers to A64 registers */ static const int bpf2a64[] = { /* return value from in-kernel function, and exit value from eBPF */ - [BPF_REG_0] = A64_R(7), + [BPF_REG_0] = A64_R(8), /* arguments from eBPF program to in-kernel function */ [BPF_REG_1] = A64_R(0), [BPF_REG_2] = A64_R(1), @@ -1048,7 +1048,7 @@ static void build_epilogue(struct jit_ctx *ctx, bool was_classic) /* Restore FP/LR registers */ emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx); - /* Move the return value from bpf:r0 (aka x7) to x0 */ + /* Move the return value from bpf:r0 (aka x8) to x0 */ emit(A64_MOV(1, A64_R(0), r0), ctx); /* Authenticate lr */ diff --git a/arch/arm64/net/bpf_timed_may_goto.S b/arch/arm64/net/bpf_timed_may_goto.S index 894cfcd7b241..a9a802711a7f 100644 --- a/arch/arm64/net/bpf_timed_may_goto.S +++ b/arch/arm64/net/bpf_timed_may_goto.S @@ -8,8 +8,8 @@ SYM_FUNC_START(arch_bpf_timed_may_goto) stp x29, x30, [sp, #-64]! mov x29, sp - /* Save BPF registers R0 - R5 (x7, x0-x4)*/ - stp x7, x0, [sp, #16] + /* Save BPF registers R0 - R5 (x8, x0-x4)*/ + stp x8, x0, [sp, #16] stp x1, x2, [sp, #32] stp x3, x4, [sp, #48] @@ -28,8 +28,8 @@ SYM_FUNC_START(arch_bpf_timed_may_goto) /* BPF_REG_AX(x9) will be stored into count, so move return value to it. */ mov x9, x0 - /* Restore BPF registers R0 - R5 (x7, x0-x4) */ - ldp x7, x0, [sp, #16] + /* Restore BPF registers R0 - R5 (x8, x0-x4) */ + ldp x8, x0, [sp, #16] ldp x1, x2, [sp, #32] ldp x3, x4, [sp, #48] diff --git a/tools/testing/selftests/bpf/progs/verifier_jit_inline.c b/tools/testing/selftests/bpf/progs/verifier_jit_inline.c index 4ea254063646..885ff69a3a62 100644 --- a/tools/testing/selftests/bpf/progs/verifier_jit_inline.c +++ b/tools/testing/selftests/bpf/progs/verifier_jit_inline.c @@ -9,7 +9,7 @@ __success __retval(0) __arch_x86_64 __jited(" addq %gs:{{.*}}, %rax") __arch_arm64 -__jited(" mrs x7, SP_EL0") +__jited(" mrs x8, SP_EL0") int inline_bpf_get_current_task(void) { bpf_get_current_task(); diff --git a/tools/testing/selftests/bpf/progs/verifier_ldsx.c b/tools/testing/selftests/bpf/progs/verifier_ldsx.c index 1026524a1983..41340877dc9d 100644 --- a/tools/testing/selftests/bpf/progs/verifier_ldsx.c +++ b/tools/testing/selftests/bpf/progs/verifier_ldsx.c @@ -274,11 +274,11 @@ __jited("movslq 0x10(%rdi,%r12), %r15") __jited("movswq 0x18(%rdi,%r12), %r15") __jited("movsbq 0x20(%rdi,%r12), %r15") __arch_arm64 -__jited("add x11, x7, x28") +__jited("add x11, x8, x28") __jited("ldrsw x21, [x11, #0x10]") -__jited("add x11, x7, x28") +__jited("add x11, x8, x28") __jited("ldrsh x21, [x11, #0x18]") -__jited("add x11, x7, x28") +__jited("add x11, x8, x28") __jited("ldrsb x21, [x11, #0x20]") __jited("add x11, x0, x28") __jited("ldrsw x22, [x11, #0x10]") diff --git a/tools/testing/selftests/bpf/progs/verifier_private_stack.c b/tools/testing/selftests/bpf/progs/verifier_private_stack.c index 646e8ef82051..c5078face38d 100644 --- a/tools/testing/selftests/bpf/progs/verifier_private_stack.c +++ b/tools/testing/selftests/bpf/progs/verifier_private_stack.c @@ -170,12 +170,12 @@ __jited(" mrs x10, TPIDR_EL{{[0-1]}}") __jited(" add x27, x27, x10") __jited(" add x25, x27, {{.*}}") __jited(" bl 0x{{.*}}") -__jited(" mov x7, x0") +__jited(" mov x8, x0") __jited(" mov x0, #0x2a") __jited(" str x0, [x27]") __jited(" bl 0x{{.*}}") -__jited(" mov x7, x0") -__jited(" mov x7, #0x0") +__jited(" mov x8, x0") +__jited(" mov x8, #0x0") __jited(" ldp x25, x27, [sp], {{.*}}") __naked void private_stack_callback(void) { @@ -220,7 +220,7 @@ __jited(" mov x0, #0x2a") __jited(" str x0, [x27]") __jited(" mov x0, #0x0") __jited(" bl 0x{{.*}}") -__jited(" mov x7, x0") +__jited(" mov x8, x0") __jited(" ldp x27, x28, [sp], #0x10") int private_stack_exception_main_prog(void) { @@ -258,7 +258,7 @@ __jited(" add x25, x27, {{.*}}") __jited(" mov x0, #0x2a") __jited(" str x0, [x27]") __jited(" bl 0x{{.*}}") -__jited(" mov x7, x0") +__jited(" mov x8, x0") __jited(" ldp x27, x28, [sp], #0x10") int private_stack_exception_sub_prog(void) {