在气体宏中自动生成xmm寄存器名称？

Question

I would like to write a gas macro to generate code containing various movdqu instructions to xmm register depending on the parameter n.

    .macro xxmov n, p1
            .if (\n == 1)
            xor %eax, %eax
            .endif
            .if (\n - 1)
            xxmov (\n - 1), \p1
            .endif
            movdqu ((\n - 1)*0x10)(\p1), %xmm0
    .endm

    xxmov 14, %rsi

Once compiled, the disassembled code is,

    0000000000000000 <.text>:
    0:              31 c0                   xor    %eax,%eax
    2:              f3 0f 6f 06             movdqu (%rsi),%xmm0
    6:              f3 0f 6f 46 10          movdqu 0x10(%rsi),%xmm0
    b:              f3 0f 6f 46 20          movdqu 0x20(%rsi),%xmm0
    10:             f3 0f 6f 46 30          movdqu 0x30(%rsi),%xmm0
    15:             f3 0f 6f 46 40          movdqu 0x40(%rsi),%xmm0
    1a:             f3 0f 6f 46 50          movdqu 0x50(%rsi),%xmm0
    1f:             f3 0f 6f 46 60          movdqu 0x60(%rsi),%xmm0
    24:             f3 0f 6f 46 70          movdqu 0x70(%rsi),%xmm0
    29:             f3 0f 6f 86 80 00 00    movdqu 0x80(%rsi),%xmm0
    30:             00
    31:             f3 0f 6f 86 90 00 00    movdqu 0x90(%rsi),%xmm0
    38:             00
    39:             f3 0f 6f 86 a0 00 00    movdqu 0xa0(%rsi),%xmm0
    40:             00
    41:             f3 0f 6f 86 b0 00 00    movdqu 0xb0(%rsi),%xmm0
    48:             00
    49:             f3 0f 6f 86 c0 00 00    movdqu 0xc0(%rsi),%xmm0
    50:             00
    51:             f3 0f 6f 86 d0 00 00    movdqu 0xd0(%rsi),%xmm0
    58:             00

However, when I replaced %xmm0 with %xmm\\n in the above xxmov macro, I got compiling error,

    $ gcc -c mac.s
mac.s: Assembler messages:
mac.s:17: Error: bad register name `%xmm(((((((((((((14 - 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm((((((((((((14 - 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm(((((((((((14 - 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm((((((((((14 - 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm(((((((((14 - 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm((((((((14 - 1)- 1)- 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm(((((((14 - 1)- 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm((((((14 - 1)- 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm(((((14 - 1)- 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm((((14 - 1)- 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm(((14 - 1)- 1)- 1)'
mac.s:17: Error: bad register name `%xmm((14 - 1)- 1)'
mac.s:17: Error: bad register name `%xmm(14 - 1)'

So, it there anyway I can manipulate my macro to xmm register name (from %xmm0 to %xmm_{n-1})? I have tried \\@ (%xmm\\@) mentioned in http://sourceware.org/binutils/docs/as/Macro.html#Macro . However, it didn't work very well because I would like to use this macro multiple time, while \\@ seems to be monotonically increasing..

Answer 1

How about rather than counting down you keep a variable to count up? Like this:

.macro xxmov n, p1, cnt=0
    .if (\cnt == 0)
        xor %eax, %eax
    .endif
    .if (\cnt != \n)
        movdqu \@*0x10(\p1), %xmm\@
        xxmov \n, \p1, (\cnt + 1)
    .endif
.endm

    xxmov 14, %rsi

Which generates:

0000000000000000 <.text>:
   0:   31 c0                       xor    %eax,%eax
   2:   f3 0f 6f 06                 movdqu (%rsi),%xmm0
   6:   f3 0f 6f 4e 10              movdqu 0x10(%rsi),%xmm1
   b:   f3 0f 6f 56 20              movdqu 0x20(%rsi),%xmm2
  10:   f3 0f 6f 5e 30              movdqu 0x30(%rsi),%xmm3
  15:   f3 0f 6f 66 40              movdqu 0x40(%rsi),%xmm4
  1a:   f3 0f 6f 6e 50              movdqu 0x50(%rsi),%xmm5
  1f:   f3 0f 6f 76 60              movdqu 0x60(%rsi),%xmm6
  24:   f3 0f 6f 7e 70              movdqu 0x70(%rsi),%xmm7
  29:   f3 44 0f 6f 86 80 00 00 00  movdqu 0x80(%rsi),%xmm8
  32:   f3 44 0f 6f 8e 90 00 00 00  movdqu 0x90(%rsi),%xmm9
  3b:   f3 44 0f 6f 96 a0 00 00 00  movdqu 0xa0(%rsi),%xmm10
  44:   f3 44 0f 6f 9e b0 00 00 00  movdqu 0xb0(%rsi),%xmm11
  4d:   f3 44 0f 6f a6 c0 00 00 00  movdqu 0xc0(%rsi),%xmm12
  56:   f3 44 0f 6f ae d0 00 00 00  movdqu 0xd0(%rsi),%xmm13

Update: Oops, that only works for the first macro usage in the file. If you need to use it more than once in the same file, it looks like using the .altmacro syntax is the way to go (it can be turned off again with .noaltmacro ):

.altmacro
.macro xxmov n, p
    .if (\n == 1)
        xor %eax, %eax
    .endif
    .if (\n > 1)
        xxmov %(\n - 1), \p
    .endif
    movdqu (\n - 1)*0x10 (%\p) , %xmm\n
.endm
    xxmov 4, rsi
    xxmov 14, rsi