Memory Question

Mistro116@yahoo.com · 12-14-2005, 01:26 PM

In C, how much code execution can be done with 256 lines of code and 24 bits of memory (including registers)? Can while loops be executed?

Thanks,
Mistro116

paulsm4 · 12-14-2005, 01:43 PM

Try it and see!

a) gcc -S
<= Generate assembly source
b) objdump -d
<= Analyze binary output
Etc etc

For extra credit, you can play with different optimization switches and see what (if any) difference they make in the resulting code size.

Your .. PSM

PS:
Yes, you can easily write a "while" loop in *one* line of C code and (I imagine) a corresponding dozen or so bytes of object code. Here's a pathological example (exactly one ix86 instruction):

C:
while (1);

ASM:
label1:
jmp label1

Matir · 12-14-2005, 02:10 PM

24 bits of memory? Probably not much. Are you including ALL registers, or just general-purpose registers? What architecture are you using?

paulsm4 · 12-14-2005, 04:07 PM

vi small.c =>

Code:

void mini ()
{
  while (1);
}

cc -S small.c; cat small.s =>

Code:

        .file   "small.c"
        .text
.globl mini
        .type   mini, @function
mini:
        pushl   %ebp
        movl    %esp, %ebp
        nop
.L2:
        jmp     .L2
        .size   mini, .-mini
        .section        .note.GNU-stack,"",@progbits
        .ident  "GCC: (GNU) 3.3.4 (pre 3.3.5 20040809)"
   <= OK: THIS IS PRETTY MUCH THE CODE WE'D EXPECT

cc -c small.c; objdump -d small.o =>

Code:

small.o:     file format elf32-i386
Disassembly of section .text:
00000000 <mini>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   90                      nop
   4:   eb fe                   jmp    4 <mini+0x4>
   <= HEY: GUESS WHAT?  EXACTLY 24 BYTES!

Sorry - not exactly 24 *bits* ;-)

And for that matter, 24 bytes/bits of *what*? You said something about "registers": registers are part of the CPU; they don't take up any RAM. We're definitely curious why you asked this question...