Re: Free x86 C compiler wanted

On 6 Apr 2007 22:59:58 -0400, George Neuner <gneuner2@comcast.net>
wrote:


>Additionally, COM files are non-relocatable and based at address
>0x100. If you load them anywhere else they don't work.
>
>[COM files can load anywhere in memory, sinec DOS sets the CS register
>to point at where they're loaded. If they're more than 64K, they do have
>to do their own segment register management. -John]


What I said previously was incomplete.


John is correct that COM files may be loaded into any segment.
Because segments can begin on any 16 byte paragraph, that means they
can be positioned pretty much anywhere in memory. However ...


COM is a raw binary format without relocation information. DOS and
CPM expect the code to begin at offset 0x100 within the load segment.
Most x86 compilers (including the OP's) produce position sensitive
code unless instructed otherwise. Unless the compiler produces
position independent code, it will not work if loaded at a different
offset.


The OP seems to be targeting an embedded system with no OS, however,
he is using an OS based compiler. He needs to be aware of the
compiler's default behavior so that he can adjust the options if
necessary.


George
--

Return to the comp.compilers page.
Search the comp.compilers archives again.