Re: macOS (Big Sur, Apple Silicon) 'make check' fails in test-crypto-tlscredsx509

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Feb 02, 2021 at 08:50:24AM -0600, Eric Blake wrote:
> On 2/1/21 11:19 PM, Roman Bolshakov wrote:
> 
> > After a session of debugging I believe there's an issue with Clang 12.
> > Here's a test program (it reproduces unexpected ASN1_VALUE_NOT_VALID
> > from _asn1_time_der() in libtasn1):
> > 
> > #include <stdio.h>
> > 
> > static int func2(char *foo) {
> >         fprintf(stderr, "%s:%d foo: %p\n", __func__, __LINE__, foo);
> >         if (foo == NULL) {
> >                 fprintf(stderr, "%s:%d foo: %p\n", __func__, __LINE__, foo);
> >                 return 1;
> >         }
> >         return 0;
> > }
> > 
> > int func1(char *foo) {
> >         int counter = 0;
> >         if (fprintf(stderr, "IO\n") > 0)
> >                 counter += 10;
> >         fprintf(stderr, "%s:%d foo: %p counter %d\n", __func__, __LINE__, foo, counter);
> >         if(!func2(foo + counter)) {
> 
> This line has unspecified behavior in the C standard.  Adding an integer
> to a pointer is only well-specified if the pointer is to an array and
> the integer is within the bounds or the slot just past the array.  But
> since you called func1(NULL), foo is NOT pointing to an array, and
> therefore foo+counter points to garbage, and the compiler is free to
> optimize it at will.
> 
> >                 fprintf(stderr, "good\n");
> >                 return 0;
> >         } else {
> >                 fprintf(stderr, "broken\n");
> >                 return 1;
> >         }
> > }
> > 
> > int main() {
> >         char *foo = NULL;
> >         return func1(foo);
> > }
> > 
> > 
> > What return value would you expect from the program?
> 
> Because the code is not strictly compliant to the C standard, I'm not
> sure what to expect.

Roman invented this example to illustrate the problem with libtasn1,
so I wonder if this suggests that libtasn1 is relying on undefined
C behaviour too.

Regards,
Daniel
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