strange level of indirection of a function call

Question

I'm writing some low level code and I noticed some unnecessary level of indirection of a function call and I simply don't get what's the reason for that indirection. Here's dummy code that reveals that behavior:

__declspec(noinline) int get_alignment(void * ptr)
{
    return 1;
}

__declspec(noinline) int test123()
{
    char buf[123];
    return get_alignment(buf);
}

Then, when I step through the code inside function test() in debugger in asm mode (Ctrl+F11) I see this:

__declspec(noinline) int test123()
{
0041FA70  sub         esp,7Ch 
    char buf[123];
    return get_alignment(buf);
0041FA73  lea         eax,[esp] 
0041FA76  push        eax  
0041FA77  call        get_alignment (40A38Fh) 
}
...
get_alignment:
0040A38F  jmp         get_alignment (41FA60h) 
...
__declspec(noinline) int get_alignment(void * ptr)
{
    return 1;
0041FA60  mov         eax,1 
}

So, the question is about that extra level of indirection: get_alignment: 0040A38F jmp get_alignment (41FA60h)

WTF is that about?! I just don't get it, it's not imported function from dll, it's a local function defined in executable. This executable compiled with all kinds of optimizations (except link time code generation). If I add static to the declaration of that get_alignment, then that extra indirection disappears. But I'm not looking for a "fix", I just wanted to understand why is that extra jump is there at all!

In my real app I actually use a function written in .asm file and I just don't get why there is extra jump generated. It seems that If I compile my code in C-mode (not C++) then I don't see that level of indirection anymore...

anybody can shed some light on that weird behavior?

Thank you!

Raymond Chen Raymond Chen · Accepted Answer · 2011-08-28T15:33:00

You probably have incremental linking enabled. An incrementally linked module "May contain jump thunks to handle relocation of functions to new addresses." http://msdn.microsoft.com/en-US/library/4khtbfyf(v=VS.80).aspx

strange level of indirection of a function call

3 Answers