Hello all,
Compiling for RISC-V, I've ran into an error like this:
tmp.c:15:3: error: 'memcpy' writing 4 bytes into a region of size 0 overflows
the destination [-Werror=stringop-overflow=]
15 | memcpy(&str2->c, &str1->c, sizeof(str2->c));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The error can be triggered by a pretty simple function:
void foo(m_struct_t *str1) {
m_struct_t *str2 = (m_struct_t *)0x123400;
memcpy(&str2->c, &str1->c, sizeof(str2->c));
}
Debugging the case, I've found the following remark in gcc/pointer-query.cc:
/* Pointer constants other than null are most likely the result
of erroneous null pointer addition/subtraction. Unless zero
is a valid address set size to zero. For null pointers, set
size to the maximum for now since those may be the result of
jump threading. */
I'd prefer not to disable this warning, as it seems very helpful, but in
embedded SW we have just too many cases we have to set an address explicitly. I
understand the concern about erroneous null pointer addition/subtraction, but I
think these could be detected in other analysis, while stringop overflow would
still work for other cases.
I see that the warning can be silenced by zero_address_valid, which is only set
for x86 non-generic address space for now. I'm not sure if this enabling zero
addresses all over the place is right for RISC-V or other potentially embedded
targets.
What do you think?
Thanks
Guy
