Re: [PATCH bpf-next v9 06/11] bpf,x86: introduce emit_store_stack_imm64() for trampoline
From: Andrii Nakryiko <hidden>
Date: 2026-01-14 01:24:05
Also in:
bpf, lkml
On Sat, Jan 10, 2026 at 6:12 AM Menglong Dong [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Introduce the helper emit_store_stack_imm64(), which is used to store a imm64 to the stack with the help of r0. Signed-off-by: Menglong Dong <redacted> --- v9: - rename emit_st_r0_imm64() to emit_store_stack_imm64() --- arch/x86/net/bpf_jit_comp.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index e3b1c4b1d550..d94f7038c441 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c@@ -1300,6 +1300,15 @@ static void emit_st_r12(u8 **pprog, u32 size, u32 dst_reg, int off, int imm) emit_st_index(pprog, size, dst_reg, X86_REG_R12, off, imm); } +static void emit_store_stack_imm64(u8 **pprog, int stack_off, u64 imm64) +{ + /* mov rax, imm64 + * mov QWORD PTR [rbp - stack_off], rax + */ + emit_mov_imm64(pprog, BPF_REG_0, imm64 >> 32, (u32) imm64);
maybe make the caller pass BPF_REG_0 explicitly, it will be more generic but also more explicit that BPF_REG_0 is used as temporary register?
+ emit_stx(pprog, BPF_DW, BPF_REG_FP, BPF_REG_0, -stack_off);
why are you negating stack offset here and not in the caller?..
quoted hunk ↗ jump to hunk
+} + static int emit_atomic_rmw(u8 **pprog, u32 atomic_op, u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size) {@@ -3352,16 +3361,14 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im * mov rax, nr_regs * mov QWORD PTR [rbp - nregs_off], rax */ - emit_mov_imm64(&prog, BPF_REG_0, 0, (u32) nr_regs); - emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -nregs_off); + emit_store_stack_imm64(&prog, nregs_off, nr_regs); if (flags & BPF_TRAMP_F_IP_ARG) { /* Store IP address of the traced function: * movabsq rax, func_addr * mov QWORD PTR [rbp - ip_off], rax */ - emit_mov_imm64(&prog, BPF_REG_0, (long) func_addr >> 32, (u32) (long) func_addr); - emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -ip_off); + emit_store_stack_imm64(&prog, ip_off, (long)func_addr);
see above, I'd pass BPF_REG_0 and -ip_off (and -nregs_off) explicitly, too many small transformations are hidden inside emit_store_stack_imm64(), IMO
}
save_args(m, &prog, regs_off, false, flags);
--
2.52.0