On Mon, 2025-01-20 at 21:35 -0700, Daniel Xu wrote:
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Hi Daniel,
> @@ -221,11 +221,13 @@ static int array_map_gen_lookup(struct bpf_map *map,
>
> *insn++ = BPF_ALU64_IMM(BPF_ADD, map_ptr, offsetof(struct bpf_array, value));
> *insn++ = BPF_LDX_MEM(BPF_W, ret, index, 0);
> - if (!map->bypass_spec_v1) {
> - *insn++ = BPF_JMP_IMM(BPF_JGE, ret, map->max_entries, 4);
> - *insn++ = BPF_ALU32_IMM(BPF_AND, ret, array->index_mask);
> - } else {
> - *insn++ = BPF_JMP_IMM(BPF_JGE, ret, map->max_entries, 3);
> + if (!inbounds) {
> + if (!map->bypass_spec_v1) {
> + *insn++ = BPF_JMP_IMM(BPF_JGE, ret, map->max_entries, 4);
> + *insn++ = BPF_ALU32_IMM(BPF_AND, ret, array->index_mask);
> + } else {
> + *insn++ = BPF_JMP_IMM(BPF_JGE, ret, map->max_entries, 3);
> + }
> }
>
> if (is_power_of_2(elem_size)) {
Note that below this hunk there is the following code:
*insn++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
*insn++ = BPF_MOV64_IMM(ret, 0);
return insn - insn_buf;
This part becomes redundant after your change. E.g. here is jit
listing for an_array_with_a_32bit_constant_0_no_nullness selftest:
JITED:
=============
func #0:
0: f3 0f 1e fa endbr64
4: 0f 1f 44 00 00 nopl (%rax,%rax)
9: 0f 1f 00 nopl (%rax)
c: 55 pushq %rbp
d: 48 89 e5 movq %rsp, %rbp
10: f3 0f 1e fa endbr64
14: 48 81 ec 08 00 00 00 subq $0x8, %rsp
1b: 31 ff xorl %edi, %edi
1d: 89 7d fc movl %edi, -0x4(%rbp)
20: 48 89 ee movq %rbp, %rsi
23: 48 83 c6 fc addq $-0x4, %rsi
27: 48 bf 00 70 58 06 81 88 ff ff movabsq $-0x777ef9a79000, %rdi
31: 48 81 c7 d8 01 00 00 addq $0x1d8, %rdi
38: 8b 46 00 movl (%rsi), %eax
3b: 48 6b c0 30 imulq $0x30, %rax, %rax
3f: 48 01 f8 addq %rdi, %rax
42: eb 02 jmp L0 //
44: 31 c0 xorl %eax, %eax // never executed
46: bf 04 00 00 00 L0: movl $0x4, %edi //
4b: 89 78 00 movl %edi, (%rax)
4e: b8 04 00 00 00 movl $0x4, %eax
53: c9 leave
54: e9 22 38 50 c3 jmp 0xffffffffc350387b
Also note that there are __arch_x86_64 and __jited tags for selftests.
These allow to match against disassembly of the generated binary code.
(See verifier_tailcall_jit.c for an example).
I think it would be good to add a test matching jited code for this feature.
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