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SubjectRe: [PATCH] Reduce stack usage in module.c
Yum Rayan wrote:
> On Tue, 29 Mar 2005 09:43:12 -0800, Randy.Dunlap <rddunlap@osdl.org> wrote:
>
>>Yum Rayan wrote:
>>
>>>Attempt to reduce stack usage in module.c (linux-2.6.12-rc1-mm3).
>>>Specifically from checkstack.pl
>
>>>Also while at it, fix following in who_is_doing_it(...)
>>>- use only as much memory is needed
>>>- do not write past array index for the boundary case
>>
>>I don't see a boundary case problem with the current code,
>>hence I don't see why the kmalloc(len + 1, GFP_KERNEL) is
>>needed...
>
>
> Let's consider the original code and len = 513
>
> 1399 static void who_is_doing_it(void)
> 1400 {
> 1401 /* Print out all the args. */
> 1402 char args[512];
> 1403 unsigned long i, len = current->mm->arg_end -
> current->mm->arg_start;
> 1404
> 1405 if (len > 512)
> 1406 len = 512;
> 1407
> 1408 len -= copy_from_user(args, (void
> *)current->mm->arg_start, len);
> 1409
> 1410 for (i = 0; i < len; i++) {
> 1411 if (args[i] == '\0')
> 1412 args[i] = ' ';
> 1413 }
> 1414 args[i] = 0;
> 1415 printk("ARGS: %s\n", args);
> 1416 }
>
> After lines 1410 thru 1413, "i" wil be 512. So line 1414 will be
> "args[512] = 0". But args is 512 byte array with last legally
> accessible element at 511?

Yes, it's so obvious (now). :)

>>File names start one level deeper than wanted. They should begin
>>with linux/ or a/ or ./ e.g.
>>There are plenty of docs on this, please let me know if you need
>>references to them.
>
>
> Point noted. Will post patch to linux/Documentation/SubmittingPatches,
> hopefully making it more clear. Reworked patch at end of email.

Good idea, thanks.

--
~Randy
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