On Wed, 14 Aug 2013 16:14:34 +0530, nidhi mittal hada said:
> 1)if i want to get value of a local variable, of a function, from stack
> trace thats bt-f output, obtained using crash ..
> No where AMD64 ABI mentions how local variables are stored ..
> is it in some specific sequence of registers ? is it in stack ?
Yes, no, maybe, depends on how smart the compiler is. Local variables
are local, and thus by definition not part of the ABI. The compiler
may decide that a given 'int' can be kept in %r8 for most of the
time, but stored at 24 bytes into the stack across 1 function call,
and another variable is in %r9 most of the time, but in that same location
24 bytes into the stack across a different function call (and that's
OK, because it always knows which variable is using that location
24 bytes into the stack when).
In some cases, a variable may even be totally optimized out of existence.
For example, if you have
int foo ( int c ) {
int a, b;
b = c * 5;
a = b + getpid();
return a;
}
the compiler can (and probably *will*) optimize both a and b
away and convert it to 'return (c*5 + getpid());'
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