Re: [PATCH] fix bug 5579: invalid long long format specifier

[John Spencer <maillist-alsa@barfooze.de>]

On 04/24/2012 08:56 PM, David Henningsson wrote:
> On 04/24/2012 12:58 PM, John Spencer wrote:
>> the attached patch fixes an invalid long long format specifier issue (%L
>> was used by mistake, which is the long double specifier).
>> this lead to abort() on 64bit system, making some of the alsa-utils
>> unusable.
>
> Thanks very much for this patch! I'm trying to access the bug tracker 
> but it seems to be down - could you explain a little where and how 
> this bug manifests itself, if you have any good test case etc?
>
it manifests itself when a POSIX compliant C library is used (i.e. not 
glibc).
musl libc's snprintf will return an error by detecting the invalid 
combination %Li

err = snprintf(res, sizeof(res), "%Li", config->u.integer64);


thus the following code is triggered

  			if (err<  0 || err == sizeof(res)) {
  				assert(0);
  				return -ENOMEM;

however, depending on how stdarg is implemented, a buggy implementation 
could eventually try to load a double from the floating point stack, 
instead of using the stack/integer registers, thus causing a crash, 
which would be even worse.