initial eax value on x86

Chris Johns chrisj at
Sat Aug 13 03:42:23 UTC 2011

On 12/08/11 2:06 AM, Philipp Eppelt wrote:
> Hello RTEMS-User,
> I am a student at Dresden University of Technology and I am currently
> working on a student project with the goal to get RTEMS working on L4
> with the help of the L4-vCPU interface.
> I have a simple HelloWorld and compiled it for i386+pc586. I load the
> hello.exe elf into my program, set the IP to the entry_point, zeroed the
> area between filesize and memsize and set the SP to the end of that area.
> So far it works. But I get a PageFault on 100018, which is the asm
> instruction:
> 00100018 cmp (%eax),%dh

Which file in RTEMS is this instruction from ?

> So after the entry point 10000c there is only one instruction touching eax:
> 00100010 dec %eax
> Initially %eax is 0, then its -1.
> This is quite confusing and I couldn't find any hint in the start.S or
> bootcard.c if eax has to be initialized with a special value.
> Or did I completely miss something?

The PC BSP assumes a boot loader. There may be some register protocol 
between the boot loader and the start up code.


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