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Jane Malalane writes ("[PATCH] xen/lib: Fix strcmp() and strncmp()"):

The C standard requires that each character be compared as unsigned
char. Xen's current behaviour compares as signed char, which changes
the answer when chars with a value greater than 0x7f are used.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jane Malalane <jane.malalane@citrix.com>

Thanks for this.

What are the practical effects of this bug ?  AFAICT in the hypervisor
code all the call sites simply test for zero/nonzero.

Of course we should fix this because

-		if ((__res = *cs - *ct++) != 0 || !*cs++)

this substraction is UB if it overflows.  So in theory the compiler
could miscompile it - although in practice I can't see how the
assumption that this doesn't overflow would "help" the compiler.

Ian.



This fix was just to make the code spec compliant and mainly for practice as I'm currently being introduced to Xen.

Jane