[ProgClub list] Memory management in C

John Elliot jj5 at progclub.org
Sun Oct 2 04:54:29 AEDT 2011


On 2/10/2011 4:39 AM, Asher Glynn wrote:
> I quite like Pascal

Ah yes, but you're from a much older version of the matrix. :)

> By convention. When I convert to machine code, after the branch I know that
> param1 is in register 1, param2 is in register2 etc. Depending on how many
> registers I've got (lots on a RISC machine) I might not need to do anything
> else. On the stack I'm passing by convention anyway, I know that param1 is
> at offset X and param 2 is at offset Y...

What I don't understand is how the compiler knows which convention to 
apply. Say for instance that I'm calling a function called 'format' that 
takes two pointers and returns a pointer (just say). The pointer values 
could be pushed onto the stack, or they could be passed in registers. 
The thing is that there will be a binary image of the 'format' function 
that I'm linking to, and it will be in machine code in some binary 
somewhere (say a .o file). The machine code of the 'format' function 
must either be implemented to receive its parameters either via the 
stack or via registers. But, in implementing the 'format' binary the 
compiler wouldn't have known anything about the state of the caller, so 
how could it know which registers, if any, were available for passing 
the arguments to 'format'? It seems to me like you'd always have to use 
the stack. I don't understand something, I'm quite sure.

> By default you statically link which involves copying most libraries into
> the eventual binary. Not desirable nowadays, so if you were writing an OS
> you'd choose to late link at load time, possibly even later than that. You'd
> possibly also (nowadays) think about extra things to help you debugging even
> if you didn't have the source or a debug copy of the binary.

Cool.

I have to say there's something about packaging up your whole app into a 
single executable that I really like. I.e. statically linking in your 
library functions. It's nice to have that level of what they call 'xcopy 
deployment'. As I recall Pascal (and Delphi) worked like that.



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