using brk to get brk_start

Question

Manual for int brk(void *end_data_segment); says: "brk() sets the end of the data segment to the value specified by end_data_segment"

On Success it returns 0 else -1.

But how to I get the init value of my break (like sbrk(0))?

best regards,

Answer 1

As the manual states:

On success, brk() returns zero. On error, -1 is returned, and errno is set to ENOMEM

So there is no way to get the initial value through a call to brk. Instead, as you noticed, you should use sbrk(0):

sbrk() increments the program's data space by increment bytes. Calling sbrk() with an increment of 0 can be used to find the current location of the program break.

There is no reason to expect brk to also provide this ability when it's already provided by sbrk(0). With that said, it may be more prudent to use use mmap in general for your memory allocation needs, due to limitations on certain operating systems for brk/sbrk.