Messages in this thread | | | From | Rasmus Villemoes <> | Date | Fri, 26 Jan 2018 10:43:16 +0100 | Subject | Re: [RFC PATCH] vsprintf: add flag ZEROPAD handling before crng is ready |
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On 26 January 2018 at 10:17, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > +Rasmus
Thanks.
> On Fri, 2018-01-26 at 15:39 +0800, Yang Shunyong wrote: >> Before crng is ready, output of "%p" composes of "(ptrval)" and >> left padding spaces for alignment as no random address can be >> generated. This seems a little strange sometimes. >> For example, when irq domain names are built with "%p", the nodes >> under /sys/kernel/debug/irq/domains like this, >> >> [root@y irq]# ls domains/ >> default irqchip@ (ptrval)-2 >> irqchip@ (ptrval)-4 \_SB_.TCS0.QIC1 \_SB_.TCS0.QIC3 >> irqchip@ (ptrval) irqchip@ (ptrval)-3 >> \_SB_.TCS0.QIC0 \_SB_.TCS0.QIC2 >> >> The name "irqchip@ (ptrval)-2" is not so readable in console >> output. > > Yes, this is not best output. > >> This patch adds ZEROPAD handling in widen_string() and move_right(). >> When ZEROPAD is set in spec, it will use '0' for padding. If not >> set, it will use ' '. >> This patch also sets ZEROPAD in ptr_to_id() before crgn is ready.
Yew.
> Have you added specific test cases to see what's going on for patterns > like > > printf("%0s\n", " (my string)");
[That's not really relevant, since we'll never have those (gcc says "warning: '0' flag used with ‘%s’").]
>> @@ -1702,6 +1709,8 @@ static char *ptr_to_id(char *buf, char *end, >> void *ptr, struct printf_spec spec) >> >> if (unlikely(!have_filled_random_ptr_key)) { >> spec.field_width = default_width; >> + spec.flags |= ZEROPAD; >> + >> /* string length must be less than default_width */ >> return string(buf, end, "(ptrval)", spec); >> }
So why not just use a string literal with the right width to begin with, e.g. =====(ptrval)===== or whatever manual padding left or right seems appropriate. Space-padding is not nice, but 0-padding isn't much better. That way you only affect the uncommon case of %p before have_filled_random_ptr_key instead of adding a few instructions to all %s users.
While at it, it may be worth looking into whether the irqdomain output actually needs the @%p thing or if one could improve that instead.
Rasmus
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