Clang has traditionally allowed C programs to implicitly convert
integers to pointers and pointers to integers, despite it not being
valid to do so except under special circumstances (like converting the
integer 0, which is the null pointer constant, to a pointer). In C89,
this would result in undefined behavior per 3.3.4, and in C99 this rule
was strengthened to be a constraint violation instead. Constraint
violations are most often handled as an error.
This patch changes the warning to default to an error in all C modes
(it is already an error in C++). This gives us better security posture
by calling out potential programmer mistakes in code but still allows
users who need this behavior to use -Wno-error=int-conversion to retain
the warning behavior, or -Wno-int-conversion to silence the diagnostic
entirely.
Differential Revision: https://reviews.llvm.org/D129881
DFSan has flags to control flows between pointers and objects referred
by pointers. For example,
a = *p;
L(a) = L(*p) when -dfsan-combine-pointer-labels-on-load = false
L(a) = L(*p) + L(p) when -dfsan-combine-pointer-labels-on-load = true
*p = b;
L(*p) = L(b) when -dfsan-combine-pointer-labels-on-store = false
L(*p) = L(b) + L(p) when -dfsan-combine-pointer-labels-on-store = true
The question is what to do with p += c.
In practice we found many confusing flows if we propagate labels from c
to p. So a new flag works like this
p += c;
L(p) = L(p) when -dfsan-propagate-via-pointer-arithmetic = false
L(p) = L(p) + L(c) when -dfsan-propagate-via-pointer-arithmetic = true
Reviewed-by: gbalats
Differential Revision: https://reviews.llvm.org/D103176
Aaron Ballman