[Bug c++/85125] constant expression with const_cast UB does not emit error
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125 --- Comment #7 from John McFarlane --- Confirmed. Thank you! On Mon, 19 Aug 2019 at 15:02, mpolacek at gcc dot gnu.org < gcc-bugzi...@gcc.gnu.org> wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125 > > Marek Polacek changed: > >What|Removed |Added > > > Status|ASSIGNED|RESOLVED > Resolution|--- |FIXED > > --- Comment #6 from Marek Polacek --- > Done for 10.1 via: > > Author: mpolacek > Date: Mon Aug 19 13:59:13 2019 > New Revision: 274671 > > URL: https://gcc.gnu.org/viewcvs?rev=274671=gcc=rev > Log: > PR c++/91264 - detect modifying const objects in constexpr. > * constexpr.c (modifying_const_object_error): New function. > (cxx_eval_call_expression): Set TREE_READONLY on a CONSTRUCTOR of > a const-qualified object after it's been fully constructed. > (modifying_const_object_p): New function. > (cxx_eval_store_expression): Detect modifying a const object > during constant expression evaluation. > (cxx_eval_increment_expression): Use a better location when > building > up the store. > (cxx_eval_constant_expression) : Mark a constant > object's constructor TREE_READONLY. > > * g++.dg/cpp1y/constexpr-tracking-const1.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const2.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const3.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const4.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const5.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const6.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const7.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const8.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const9.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const10.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const11.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const12.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const13.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const14.C: New test. > > Added: > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const1.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const10.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const11.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const12.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const13.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const14.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const2.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const3.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const4.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const5.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const6.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const7.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const8.C > trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const9.C > Modified: > trunk/gcc/cp/ChangeLog > trunk/gcc/cp/constexpr.c > trunk/gcc/testsuite/ChangeLog > > -- > You are receiving this mail because: > You are on the CC list for the bug. > You reported the bug.
[Bug c++/85125] constant expression with const_cast UB does not emit error
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125 Marek Polacek changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED --- Comment #6 from Marek Polacek --- Done for 10.1 via: Author: mpolacek Date: Mon Aug 19 13:59:13 2019 New Revision: 274671 URL: https://gcc.gnu.org/viewcvs?rev=274671=gcc=rev Log: PR c++/91264 - detect modifying const objects in constexpr. * constexpr.c (modifying_const_object_error): New function. (cxx_eval_call_expression): Set TREE_READONLY on a CONSTRUCTOR of a const-qualified object after it's been fully constructed. (modifying_const_object_p): New function. (cxx_eval_store_expression): Detect modifying a const object during constant expression evaluation. (cxx_eval_increment_expression): Use a better location when building up the store. (cxx_eval_constant_expression) : Mark a constant object's constructor TREE_READONLY. * g++.dg/cpp1y/constexpr-tracking-const1.C: New test. * g++.dg/cpp1y/constexpr-tracking-const2.C: New test. * g++.dg/cpp1y/constexpr-tracking-const3.C: New test. * g++.dg/cpp1y/constexpr-tracking-const4.C: New test. * g++.dg/cpp1y/constexpr-tracking-const5.C: New test. * g++.dg/cpp1y/constexpr-tracking-const6.C: New test. * g++.dg/cpp1y/constexpr-tracking-const7.C: New test. * g++.dg/cpp1y/constexpr-tracking-const8.C: New test. * g++.dg/cpp1y/constexpr-tracking-const9.C: New test. * g++.dg/cpp1y/constexpr-tracking-const10.C: New test. * g++.dg/cpp1y/constexpr-tracking-const11.C: New test. * g++.dg/cpp1y/constexpr-tracking-const12.C: New test. * g++.dg/cpp1y/constexpr-tracking-const13.C: New test. * g++.dg/cpp1y/constexpr-tracking-const14.C: New test. Added: trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const1.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const10.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const11.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const12.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const13.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const14.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const2.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const3.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const4.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const5.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const6.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const7.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const8.C trunk/gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const9.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/constexpr.c trunk/gcc/testsuite/ChangeLog
[Bug c++/85125] constant expression with const_cast UB does not emit error
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125
Marek Polacek changed:
What|Removed |Added
Keywords||patch
Status|NEW |ASSIGNED
CC||mpolacek at gcc dot gnu.org
Assignee|unassigned at gcc dot gnu.org |mpolacek at gcc dot
gnu.org
--- Comment #5 from Marek Polacek ---
Recently I posted a patch for this:
https://gcc.gnu.org/ml/gcc-patches/2019-07/msg01914.html
With that, the original testcase now gives:
85125.C:6:22: error: non-constant condition for static assertion
6 | static_assert(f()==77, "");
| ~~~^~~~
85125.C:6:20: in ‘constexpr’ expansion of ‘f()’
85125.C:3:27: error: modifying a const object ‘(int&)(& i)’ is not allowed in a
constant expression
3 | const_cast(i) = 88;
| ^~~~
85125.C:2:17: note: originally declared ‘const’ here
2 | int const i = 77;
| ^
and the one from Comment 3 gives:
85125-2.C:12:16: error: non-constant condition for static assertion
12 | static_assert(f());
| ~^~
85125-2.C:12:16: in ‘constexpr’ expansion of ‘f()’
85125-2.C:8:12: error: modifying a const object ‘*(int*)s.S::ptr’ is not
allowed in a constant expression
8 | *s.ptr = 2;
| ~~~^~~
85125-2.C:7:16: note: originally declared ‘const’ here
7 | auto const s = S{};
|^
[Bug c++/85125] constant expression with const_cast UB does not emit error
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125 --- Comment #4 from David Stone --- *** Bug 86623 has been marked as a duplicate of this bug. ***
[Bug c++/85125] constant expression with const_cast UB does not emit error
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125
David Stone changed:
What|Removed |Added
CC||david at doublewise dot net
--- Comment #3 from David Stone ---
Here is a reproduction that does not require const_cast:
struct S {
int a = 1;
int * ptr =
};
constexpr bool f() {
auto const s = S{};
*s.ptr = 2;
return s.a == 2;
}
static_assert(f());
See it live: https://godbolt.org/z/30O7_j
[Bug c++/85125] constant expression with const_cast UB does not emit error
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125
--- Comment #2 from John McFarlane ---
Here are two more:
constexpr int dubious_increment(int i) { return ++i + ++i; }
static_assert(dubious_increment(0) == 3);
constexpr int dubious_increment(int i) { return i; }
static_assert(dubious_increment(0) == 2);
The former might be a special case because it produces warnings when compiled
at a high-enough warning level (-Wall) but continues to compile nevertheless.
(Clan, warns at any level but also happily compiles.) The second just compiles
without warning no matter what.
Would these be classes as the same issue or should I submit a separate report?
Also, I'm not trying very hard to find these so I suspect there are more.
[Bug c++/85125] constant expression with const_cast UB does not emit error
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85125 Jonathan Wakely changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2018-04-03 Ever confirmed|0 |1 --- Comment #1 from Jonathan Wakely --- N.B. GCC 5.x releases are no longer supported, but this bug is still present in current releases.
