Accessing an array with inline assembly using AT&T syntax

Question

I want to assign an array using inline assembly using the AT&T syntax. I want to achieve something like the following. Note that rsp here is the %rsp register.

long saved_sp[N];
long new_sp[N];

void some_function( unsigned int tid, ... )
{
 // These two lines should be in assembly
 saved_sp[tid] = rsp; 
 rsp = new_sp[tid];   
 ......
}

Brett Hale · Accepted Answer · 2011-11-25 17:25:57Z

3

I'm sure I don't need to warn you...

__asm__ __volatile__ (

    "movq %%rsp, (%0, %2, 8)\n\t"
    "movq (%1, %2, 8), %%rsp\n\t"

    : : "r" (saved_sp), "r" (new_sp), "r" ((long) tid));

Perhaps "memory" should be added as a clobber, but it seems kind of redundant. Wherever you go after this, remember that the frame pointer "%rbp" will be invalidated.

answered Nov 25, 2011 at 17:25

Brett Hale

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1 Comment

MetallicPriest Over a year ago

Oh Ok, I got what your are trying to do :)!

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