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 <puranjay@kernel.org>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260513045153.2402197-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 0816c40fc7af95b46da39a171b848b17c5d606e8..085e650662e3dd7c5e57453c7e48e467fda5edfd 100644 (file)
--- 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 894cfcd7b2416dd738521e0245ed6e17fca2be28..a9a802711a7f9dc84b7d3644112e9577a7c4cebd 100644 (file)
--- 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 4ea25406364674a6a4d0be109c276f48cf3cb173..885ff69a3a620428550e785263ce427a476735fe 100644 (file)
--- 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 1026524a1983c60cad9f670c1d8493ed028ef704..41340877dc9d97a75b127b3808fa7c047039115c 100644 (file)
--- 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 646e8ef820510d017a655d63b719a065a43d2aa5..c5078face38dadac9a68f859e8471d79843a3cd9 100644 (file)
--- 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)
 {