Re: Huge numbers for incr passed to _sbrk

[Emeka <emekamicro at gmail dot com>]

Can you share what you are doing with me ?

On Thu, Aug 16, 2018, 8:31 AM Michael Mamic <michael.mamic77@gmail.com>
wrote:

> Hello,
>
> I am making a bare metal operating system for then Raspberry Pi, using
> newlib as the standard library. I have implemented all of the syscalls
> without trouble, the exception being _sbrk which always yields an error. My
> simple implementation is below:
>
> uint32_t sbrk(int incr) {
>     highest_addr+=incr;
>     if(highest_addr > 0x20000000) {
>         errno = ENOMEM;
>         return -1;
>     }
>     return highest_addr;
> }
>
> This implementation of sbrk is seemingly fine, but sbrk itself is called
> with an incredibly large value for incr, 1431656813. This huge number
> causes my memory to immediately overflow. After debugging, I have found
> with almost absolute certainty that this call to sbrk comes when I call
> printf, sometime before the text is sent to _write for dislay. My
> installation of newlib comes from the libnewlib debian package, and it is
> on the most recent update.
>
> What could be the problem here, and is my implementation of sbrk adequate?
>