将结构偏移量属性赋予汇编器 [英] give structure offset attribute to assembler

问题描述

如何将C结构的偏移量发送到汇编代码? 例如

how can I send the offset of a C struct to en assembly code ? For example

在我的C代码中，

typedef struct
{
  unsigned int a;
  unsigned int b;
} CMyStruct;

我将CMyStruct结构的指针发送给ASM函数 假设我的指针进入R0

I send to an ASM function a pointer of a CMyStruct structure Let suppose that my pointer is into R0

要访问a和b属性，我需要这样做.

To access to a and b attribute I need to do that.

ldr      r1, [r0, #0] // read a
ldr      r2, [r0, #4] // read b

总有没有将#0和#4指定为连续值吗? 像

Is there anyway to not specify #0 and #4 as contant value ? Something like

ldr      r1, [r0, CMyStruct.a] // read a
ldr      r2, [r0, CMyStruct.b] // read b

谢谢 艾蒂安(Etienne)

Thank's Etienne

推荐答案

实际上有一种方法.解决方案是包含一点魔力，但它是可行的.就是这样.

There is a way, actually. The solution is contains a little bit of magic, but it's works. It's just works.

在c文件中:

#define DEFINE(sym, val) asm volatile("\n-> " #sym " %0 " #val "\n" : : "i" (val))
#define OFFSETOF(s, m) \
    DEFINE(offsetof_##s##_##m, offsetof(s, m));

#define SIZEOF(s) \
    DEFINE(sizeof_##s, sizeof(s));

void foo()
{
    OFFSETOF(KERNEL, error);
    OFFSETOF(KERNEL, pool);
    SIZEOF(KERNEL);
}

在Makefile中:

in Makefile:

asm_defines.h: asm_defines.c
    $(GCC) $(FLAGS_CC) -S $< -o - | awk '($$1 == "->") { print "#define " $$2 " " $$3 }' > $(BUILD_DIR)/$@

最后，您将获得asm_defines.h，您可以将其包含在.S文件中.

Finally you will got asm_defines.h, which you can include in your .S file.

#define offsetof_KERNEL_error #16
#define offsetof_KERNEL_pool #4
#define sizeof_KERNEL #120

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