gdb：打印AArch64高级SIMD向量寄存器（可能吗？）

Question

我试图在我的汇编代码中调试，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断点，运行layout asm并使用si逐步执行我的指令。但是，当我达到我想要的指令时，例如p v16，没有在该寄存器中打印该值，它给出了如下错误：

       │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，所以对于很多人来说这个问题似乎也很简单。

Answer 1

尝试info vector用于所有高级SIMD寄存器（以各种布局打印），或info all-registers v16仅用于v16的内容。

Answer 2

您也可以在gdb中打印矢量寄存器，如下例所示。

(gdb) p $v0
$101 = {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}}}

打印不同的通道/元素：

(gdb) p $v0.q
$102 = {u = {0x01010103030103050607010706010307}, s = {0x01010103030103050607010706010307}}
(gdb) p $v0.d
$103 = {f = {1.2672947890318689e-279, 7.7486181465248912e-304}, u = {434317018741670663, 72340181461566213}, s = {434317018741670663, 72340181461566213}}
(gdb) p $v0.s
$104 = {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
$105 = {0x01010103030103050607010706010307}
(gdb) p $v0.d.s
$106 = {434317018741670663, 72340181461566213}
(gdb) p $v0.d.s[1]
$107 = 72340181461566213

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

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

Answer 3

的ARMv7

这是ARMv7的行为，类似于上面提到的ARMv8：https://stackoverflow.com/a/38538116/9160762，QEMU v3.0.0源自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
$3 = {
  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
$5 = {[0] = 1.5, [1] = 2.5, [2] = 3.5, [3] = 4.5}

Test setup。

与info register的错误

当我尝试在info vector中提到的此设置（v7或v8）中使用info register或https://stackoverflow.com/a/35552000/9160762时，似乎存在浮点表示转换为整数的错误，请参阅：https://reverseengineering.stackexchange.com/questions/8992/floating-point-registers-on-arm/20623#20623

ALL

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