Am 28.02.2012 13:27, schrieb Ralf Friedl:
> walter harms wrote:
>> Enabling the fast proc scan code for linux2.4 causes top
>> to display strange numbers [see:possible bug in proc fast scan code]
>>
>> the reason for this is that the last char in proc/$$/stat is "\n".
>> This is no problem for > 2.4 since the stats line contains additional
>> chars.
>>
>> Please be aware that the current code does NOT stop at \0 ! adding more
>> tokens to read will cause the code to read beyond \0 !
>>
>> i also killed the variable c what saves 1 byte.
>>
> This variable would live on the stack if it would ever leave the
> register (which it doesn't, even on a x86 with very few registers).
>
> Independent of this patch, you do realize that initializing n to
> *str-'0' is some kind of manual loop unrolling? Both of the following
> versions are smaller, at the cost of one more pass through the loop. I
> don't know whether it is called often enough for this to matter.
> The first version is smaller with -O9 -m32, -Os -m32 and -Os -m64 while
> it is larger with -O9 -m64 with GCC 4.6.2. In each case both versions
> are smaller than the original.
>
> unsigned long fast_strtoul_10(char **endptr)
> {
> char c;
> char *str = *endptr;
> unsigned long n = 0;
>
> while ((c = *str++) > ' ')
> n = n*10 + (c - '0');
>
> *endptr = str; /* We skip trailing space! */
> return n;
> }
>
> unsigned long fast_strtoul_10(char **endptr)
> {
> char c;
> char *str = *endptr;
> unsigned long n = 0;
>
> while (*str > ' ')
> n = n*10 + (*str++ - '0');
>
> *endptr = str + 1; /* We skip trailing space! */
> return n;
> }
>
>
Hello Ralf,
the current version has a major problem when you consider this: "0\0"
the patch ( change != into > ) will only catch the current bug
(reading the last 0 wrong what actually happens on 2.4) but when the main
code reads again (perhaps to get additional information) it will read
beyond \0.
char *cp="0\n";
fast_strtoul_10(&cp); <-- will work fine
fast_strtoul_10(&cp); <-- will break
re
wh
_______________________________________________
busybox mailing list
busybox@busybox.net
http://lists.busybox.net/mailman/listinfo/busybox
