Comment by gpderetta
2 days ago
Casting a char pointer to a vector pointer and doing vector loads doesn't violate provenance, although it might violate TBAA.
Regarding provenance, consider this:
void bar();
int foo() {
int * ptr = malloc(sizeof(int));
*ptr = 10;
bar();
int result = *ptr;
free(ptr);
return result;
}
If the compiler can track the lifetime of the dynamically allocated int, it can remove the allocation and covert this function to simply
int foo() {
bar();
return 10;
}
It can't if arbitrary code (for example inside bar()) can forge pointers to that memory location. The code can seem silly, but you could end up with something similar after inlining.
> It can't if arbitrary code (for example inside bar()) can forge pointers to that memory location.
Yes. It absolutely can. What are you even talking about?
C is not the Windows Start Menu. This habit of thinking it needs to do what it thinks I might expect instead of what I told it is deeply psychotic.
I litterally have no idea what are you trying to say. Do you mean that bar should be allowed to access *ptr with impunity or not?
I'm not trying to say anything. I said and meant exactly what I said. No more, no less. Your logic is obviously flawed. There is nothing preventing that optimization in the presence of a forged pointer in bar().
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