gdb：打印 AArch64 高级 SIMD 向量寄存器（可能吗？）

Question

我正在尝试调试我的汇编代码以检查高级 SIMD 向量寄存器中的值。为此，我运行 gdb 并在我的指令中设置了一个断点，运行 layout asm 并使用 si 单步执行我的指令。然而，当我到达我想要的指令时，例如 p v16，没有打印这个寄存器内的值，它给了我一个如下所示的错误：

       │0x4009d0 <Montmul512+80>        umull2 v16.2d, v15.4s, v7.s[3]                                                                         │
      >│0x4009d4 <Montmul512+84>        umull2 v17.2d, v13.4s, v7.s[3]                                                                         │
       │0x4009d8 <Montmul512+88>        umull2 v18.2d, v14.4s, v7.s[3]                                                                         │
       │0x4009dc <Montmul512+92>        umull2 v19.2d, v12.4s, v7.s[3]                                                                         │
       │0x4009e0 <Montmul512+96>        umull  v20.2d, v15.2s, v7.s[3]                                                                         │
       │0x4009e4 <Montmul512+100>       umull  v21.2d, v13.2s, v7.s[3]                                                                         │
       │0x4009e8 <Montmul512+104>       umull  v22.2d, v14.2s, v7.s[3]                                                                         │
       └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
    (gdb) print v16
    print v16
    No symbol "v16" in current context.

我没有任何调试汇编代码的经验，所以也许这个问题对很多人来说似乎很简单。

Answer 1

对所有高级 SIMD 寄存器（以各种布局打印）尝试info vector，或对 v16 的内容尝试info all-registers v16。

Answer 2

您还可以从 gdb 中打印向量寄存器，如下例所示。

(gdb) p $v0
1 = {d = {f = {1.2672947890318689e-279, 7.7486181465248912e-304}, u = {434317018741670663, 72340181461566213}, s = {434317018741670663, 72340181461566213}}, s = {
    f = {2.42644275e-35, 2.53914328e-35, 3.79131591e-37, 2.36942839e-38}, u = {100729607, 101122311, 50397957, 16843011}, s = {100729607, 101122311, 50397957, 
      16843011}}, h = {u = {775, 1537, 263, 1543, 773, 769, 259, 257}, s = {775, 1537, 263, 1543, 773, 769, 259, 257}}, b = {u = {7, 3, 1, 6, 7, 1, 7, 6, 5, 3, 1, 3, 
      3, 1, 1, 1}, s = {7, 3, 1, 6, 7, 1, 7, 6, 5, 3, 1, 3, 3, 1, 1, 1}}, q = {u = {0x01010103030103050607010706010307}, s = {0x01010103030103050607010706010307}}}

打印不同 lanes/elements:

(gdb) p $v0.q
2 = {u = {0x01010103030103050607010706010307}, s = {0x01010103030103050607010706010307}}
(gdb) p $v0.d
3 = {f = {1.2672947890318689e-279, 7.7486181465248912e-304}, u = {434317018741670663, 72340181461566213}, s = {434317018741670663, 72340181461566213}}
(gdb) p $v0.s
4 = {f = {2.42644275e-35, 2.53914328e-35, 3.79131591e-37, 2.36942839e-38}, u = {100729607, 101122311, 50397957, 16843011}, s = {100729607, 101122311, 50397957, 
    16843011}}
(gdb) p $v0.q.s
5 = {0x01010103030103050607010706010307}
(gdb) p $v0.d.s
6 = {434317018741670663, 72340181461566213}
(gdb) p $v0.d.s[1]
7 = 72340181461566213

根据我使用 -tui、layout asm、layout reg 的经验，如果您没有非常大的显示器，则选项往往会很拥挤。因此，如果您在 gdb 中执行以下命令，您将很难看到所有 simd 寄存器。由于我很懒惰，所以我倾向于使用缩写。当 Gdb 不理解您想要的命令时，它会通知您。

(gdb) wh reg +1
(gdb) tu reg next

Answer 3

ARMv7

这是类似于 ARMv8 中提到的 ARMv7 行为： with QEMU v3.0.0 built from source user mode + GDB 8.2 Ubuntu 16.04.

加载后：

1.5, 2.5, 3.5, 4.5

进入 q0，我们有：

(gdb) p $q0
 = {
  u8 = {[0] = 0, [1] = 0, [2] = 192, [3] = 63, [4] = 0, [5] = 0, [6] = 32, [7] = 64, [8] = 0, [9] = 0, [10] = 96, [11] = 64, [12] = 0, [13] = 0, [14] = 144, [15] = 64}, 
  u16 = {[0] = 0, [1] = 16320, [2] = 0, [3] = 16416, [4] = 0, [5] = 16480, [6] = 0, [7] = 16528}, 
  u32 = {[0] = 1069547520, [1] = 1075838976, [2] = 1080033280, [3] = 1083179008}, 
  u64 = {[0] = 4620693218751676416, [1] = 4652218416153755648}, 
  f32 = {[0] = 1.5, [1] = 2.5, [2] = 3.5, [3] = 4.5}, 
  f64 = {[0] = 8.0000018998980522, [1] = 1024.0002455711365}
}

和：

(gdb) p $q0.f32
 = {[0] = 1.5, [1] = 2.5, [2] = 3.5, [3] = 4.5}

Test setup.

错误 info register

当我尝试在此设置（v7 或 v8）中使用 info vector 或 info register 时，如 , there seems to be a bug where the floating point representation gets converted to integer, see: https://reverseengineering.stackexchange.com/questions/8992/floating-point-registers-on-arm/20623#20623

中所述

SVE

尚未在 QEMU 上实现，请参阅：How to assemble ARM SVE instructions with GNU GAS or LLVM and run it on QEMU?

gdb：打印 AArch64 高级 SIMD 向量寄存器（可能吗？）

gdb: print AArch64 advanced SIMD vector registers (is it possible?)

gcc

assembly

gdb

arm

arm64