| Using the GNU Compiler Collection (GCC): Return Address |
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These functions may be used to get information about the callers of a function.
This function returns the return address of the current function, or of
one of its callers. The level argument is number of frames to
scan up the call stack. A value of 0 yields the return address
of the current function, a value of 1 yields the return address
of the caller of the current function, and so forth. When inlining
the expected behavior is that the function returns the address of
the function that is returned to. To work around this behavior use
the noinline function attribute.
The level argument must be a constant integer.
On some machines it may be impossible to determine the return address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function returns 0 or a
random value. In addition, __builtin_frame_address may be used
to determine if the top of the stack has been reached.
Additional post-processing of the returned value may be needed, see
__builtin_extract_return_addr.
Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program. As a result, calls that are considered unsafe are diagnosed when the -Wframe-address option is in effect. Such calls should only be made in debugging situations.
The address as returned by __builtin_return_address may have to be fed
through this function to get the actual encoded address. For example, on the
31-bit S/390 platform the highest bit has to be masked out, or on SPARC
platforms an offset has to be added for the true next instruction to be
executed.
If no fixup is needed, this function simply passes through addr.
This function does the reverse of __builtin_extract_return_addr.
This function is similar to __builtin_return_address, but it
returns the address of the function frame rather than the return address
of the function. Calling __builtin_frame_address with a value of
0 yields the frame address of the current function, a value of
1 yields the frame address of the caller of the current function,
and so forth.
The frame is the area on the stack that holds local variables and saved
registers. The frame address is normally the address of the first word
pushed on to the stack by the function. However, the exact definition
depends upon the processor and the calling convention. If the processor
has a dedicated frame pointer register, and the function has a frame,
then __builtin_frame_address returns the value of the frame
pointer register.
On some machines it may be impossible to determine the frame address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function returns 0 if
the first frame pointer is properly initialized by the startup code.
Calling this function with a nonzero argument can have unpredictable effects, including crashing the calling program. As a result, calls that are considered unsafe are diagnosed when the -Wframe-address option is in effect. Such calls should only be made in debugging situations.
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