Variables assigned to ram are increasing elf file size (=> occupying flash)

Dan Kegel dank@kegel.com
Tue Sep 1 15:41:45 GMT 2020


Unless they're initialized, the arrays should be in BSS, which shouldn't be
in the elf nor stored to flash (since it's all zero, and should be cleared
on startup).

Since you didn't include a test case, here's a tiny example:

dank@thinky:~$ cat foo.c
#include <stdio.h>
#include <stdlib.h>
int blarg[500000];

int main(int argc, char **argv)
{
   int i = atoi(argv[1]);
   int j = atoi(argv[2]);
   blarg[i] = 7;
   printf("blarg[%d] == %d\n", j, j);
   return 0;
}
dank@thinky:~$ gcc -O2 foo.c
dank@thinky:~$ size a.out
   text   data    bss    dec    hex filename
   1783    608 2000032 2002423 1e8df7 a.out
dank@thinky:~$ ls -l a.out
-rwxrwxr-x 1 dank dank 16768 Sep  1 08:39 a.out

Note the small size of a.out.
- Dan

On Tue, Sep 1, 2020 at 3:21 AM Rachel Sapir <rachel@agito.co.il> wrote:

> Hello,
>
> I noticed that when I increase array sizes (I have some very big arrays)
> the .elf file is increased by the same size. Since the elf file is saved to
> the flash, it occupies flash area unnecessarily.
>
> Is there a way to prevent this from happening?
>
> Best regards,
> Rachel
>
>


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