Repository navigation
Do not emit AVX instructions for UEFI target #7885
Description
While working on porting my bootloader to Zig, I hit issues with #UD (undefined opcode) exceptions in my program. The following minimal Zig code will cause the error when not compiled in one of the release modes.
const std = @import("std");
const uefi = std.os.uefi;
pub fn main() uefi.Status {
var buf: [64]u16 = undefined;
while (true) {}
}The issue is with the following assembly, which looks to be doing a memset-like routine on buf using AVX isntructions:
// main()
470: 55 push rbp
471: 48 81 ec b0 00 00 00 sub rsp,0xb0
478: 48 8d ac 24 80 00 00 lea rbp,[rsp+0x80]
47f: 00
480: 48 8d 45 a8 lea rax,[rbp-0x58]
484: 48 89 c1 mov rcx,rax
487: ba aa 00 00 00 mov edx,0xaa
48c: 41 b8 80 00 00 00 mov r8d,0x80
492: e8 b9 00 00 00 call 0x550
497: eb fe jmp 0x497
499: 0f 1f 80 00 00 00 00 nop DWORD PTR [rax+0x0]
// memset
550: 48 89 c8 mov rax,rcx
553: 4d 85 c0 test r8,r8
556: 74 64 je 0x5bc
558: 49 81 f8 80 00 00 00 cmp r8,0x80
55f: 73 05 jae 0x566
561: 45 31 c9 xor r9d,r9d
564: eb 4a jmp 0x5b0
566: c5 f9 6e c2 vmovd xmm0,edx
56a: 4d 89 c1 mov r9,r8
56d: 31 c9 xor ecx,ecx
56f: 49 83 e1 80 and r9,0xffffffffffffff80
573: c4 e2 7d 78 c0 vpbroadcastb ymm0,xmm0 // ===== #UD EXCEPTION HERE =====
578: 0f 1f 84 00 00 00 00 nop DWORD PTR [rax+rax*1+0x0]
57f: 00
580: c5 fe 7f 04 08 vmovdqu YMMWORD PTR [rax+rcx*1],ymm0
585: c5 fe 7f 44 08 20 vmovdqu YMMWORD PTR [rax+rcx*1+0x20],ymm0
58b: c5 fe 7f 44 08 40 vmovdqu YMMWORD PTR [rax+rcx*1+0x40],ymm0
591: c5 fe 7f 44 08 60 vmovdqu YMMWORD PTR [rax+rcx*1+0x60],ymm0
597: 48 83 e9 80 sub rcx,0xffffffffffffff80
59b: 49 39 c9 cmp r9,rcx
59e: 0f 85 dc ff ff ff jne 0x580
5a4: 4d 39 c1 cmp r9,r8
5a7: 0f 84 0f 00 00 00 je 0x5bc
5ad: 0f 1f 00 nop DWORD PTR [rax]
5b0: 42 88 14 08 mov BYTE PTR [rax+r9*1],dl
5b4: 49 ff c1 inc r9
5b7: 4d 39 c8 cmp r8,r9
5ba: 75 f4 jne 0x5b0
5bc: c5 f8 77 vzeroupper
5bf: c3 retSince enabling AVX isn't a part of the state for x64 UEFI apps defined by the spec, this target should probably default to not using AVX.
Activity