From: Denis Efremov
Sent: 01 October 2019 16:13
...
Just found an official documentation to this issue: https://gcc.gnu.org/gcc-4.9/porting_to.html "Null pointer checks may be optimized away more aggressively ... The pointers passed to memmove (and similar functions in <string.h>) must be non-null even when nbytes==0, so GCC can use that information to remove the check after the memmove call. Calling copy(p, NULL, 0) can therefore deference a null pointer and crash."
Right, so just don't code a NULL pointer test after a memcpy() call. There is no need to avoid the call itself.
But again, I would say that the bug in this code is because the if condition was copy-pasted and it should be inverted.
Oh, the code is question is just stupidly bad. It seemed to do: if (a) x; else if (!a) y; else error ("all borked")
If the whole driver is written like that it needs fixing before anyone takes a serious look at it.
David
- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)