Question

我正在尝试使用内联汇编将一堆结构成员（Particle是指向此类结构的指针）加载到某些寄存器中。这是我最初的解决方案：

asm("mov    %1(%0), %%edx\n"
    "fld    %2(%0)\n"
    "fld    %3(%0)\n"
    "fld    %4(%0)\n"
    "fld    %5(%0)\n"
    "movups %6(%0), %%xmm1\n"
    "movups %7(%0), %%xmm2\n"
    "movups %8(%0), %%xmm3\n"
    "movups %9(%0), %%xmm4\n"
    :
    : "r" (Particle),
        "n" (offsetof(ptcParticle, Active)),
        "n" (offsetof(ptcParticle, Size)),
        "n" (offsetof(ptcParticle, Rotation)),
        "n" (offsetof(ptcParticle, Time)),
        "n" (offsetof(ptcParticle, TimeScale)),
        "n" (offsetof(ptcParticle, Colour)),
        "n" (offsetof(ptcParticle, Location)),
        "n" (offsetof(ptcParticle, Velocity)),
        "n" (offsetof(ptcParticle, Accel))
    : "%edx", "%st", "%st(1)", "%st(2)", "%st(3)", "%xmm1", "%xmm2",
        "%xmm3", "%xmm4"
);

但它不起作用，因为GCC将这些偏移输出为立即数字文字，如下所示：

mov     $0(%eax), %edx
fld     $44(%eax)
fld     $40(%eax)
fld     $8(%eax)
fld     $4(%eax)
movups  $12(%eax), %xmm1
movups  $28(%eax), %xmm2
movups  $48(%eax), %xmm3
movups  $60(%eax), %xmm4

因此，gas将(%eax)视为表达后的垃圾：

Error: junk `(%eax)' after expression

如果我只能摆脱输出中的美元符号，这将有效。知道如何访问结构成员吗？

Answer 1

好的，我已经明白了 - 需要%c运营商。我写过这个帮手宏：

#define DECLARE_STRUCT_OFFSET(Type, Member)     \
    [Member] "i" (offsetof(Type, Member))

并像这样使用它：

    asm("mov    %c[Active](%0), %%edx\n"
        "fld    %c[Size](%0)\n"
        "fld    %c[Rotation](%0)\n"
        "fld    %c[Time](%0)\n"
        "fld    %c[TimeScale](%0)\n"
        "movups %c[Colour](%0), %%xmm1\n"
        "movups %c[Location](%0), %%xmm2\n"
        "movups %c[Velocity](%0), %%xmm3\n"
        "movups %c[Accel](%0), %%xmm4\n"
        :
        : "r" (Particle),
            DECLARE_STRUCT_OFFSET(ptcParticle, Active),
            DECLARE_STRUCT_OFFSET(ptcParticle, Size),
            DECLARE_STRUCT_OFFSET(ptcParticle, Rotation),
            DECLARE_STRUCT_OFFSET(ptcParticle, Time),
            DECLARE_STRUCT_OFFSET(ptcParticle, TimeScale),
            DECLARE_STRUCT_OFFSET(ptcParticle, Colour),
            DECLARE_STRUCT_OFFSET(ptcParticle, Location),
            DECLARE_STRUCT_OFFSET(ptcParticle, Velocity),
            DECLARE_STRUCT_OFFSET(ptcParticle, Accel)
        : "%edx", "%st", "%st(1)", "%st(2)", "%st(3)", "%xmm1", "%xmm2",
            "%xmm3", "%xmm4"
    );

现在生成的程序集正确，一切似乎都有效。

从内联汇编访问结构成员？

1 个答案: