[Bug c/110399] New: pointer substraction causes coredump with ftrapv on edge case

[Bug c/110399] New: pointer substraction causes coredump with ftrapv on edge case

[baiwfg2 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110399

            Bug ID: 110399
           Summary: pointer substraction causes coredump with ftrapv on
                    edge case
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: baiwfg2 at gmail dot com
  Target Milestone: ---

The demo code is :

```c
#include <stdio.h>
#include <stdint.h>
#include <signal.h>
#include <assert.h>

int main() {
    {
        char *p = (char *)0x80000001;
        char *q = (char *)0x7fffffff;
        uint32_t w = p - q;
        printf("32 bit, w1=%u\n", w);
    }

    {
        char *p = (char *)0x7fffffffffffffff;
        char *q = (char *)0x7ffffffffffffffd;
        uint32_t w2 = p - q;
        printf("w2=%u\n", w2);
    }

    {
        char *p = (char *)0x8000000000000003;
        char *q = (char *)0x8000000000000001;
        uint32_t w3 = p - q;
        printf("w3=%u\n", w3);
    }

    {
        char *p = (char *)0x8000000000000001;
        char *q = (char *)0x0000000000000001;
        uint32_t w4 = p - q;
        printf("w4=%u\n", w4); // ans is 0, not crash under -ftrapv
    }

    {
        char *p = (char *)0x8000000000000001;
        char *q = (char *)0x7fffffffffffffff;
        uint32_t w5 = (uintptr_t)p - (uintptr_t)q;
        printf("w5=%u\n", w5);
    }

    {
        char *p = (char *)0x8000000000000001; // use uint8_t also crash
        char *q = (char *)0x7fffffffffffffff; // use smaller num
0x0000000000000011, also crash
        uint32_t w6 = p - q;
        printf("w6=%u\n", w6); // crash under gcc -ftrapv, not crash under
clang -ftrapv
    }

    return 0;
}
```

The statement w6 = p - q cause coredump. But what program actually means do
pointer unsigned arithmetic operation. How can I make it right(that is, output
2) with ftrapv option ? I find it's ok with clang -ftrapv .

This happens on many gcc versions.

[Bug middle-end/110399] pointer substraction causes coredump with ftrapv on edge case

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110399

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
32 bit, w1=2
w2=2
w3=2
w4=0
w5=2

Program received signal SIGABRT, Aborted.

[Bug middle-end/110399] pointer substraction causes coredump with ftrapv on edge case

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110399

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 13421.

*** This bug has been marked as a duplicate of bug 13421 ***

[Bug middle-end/110399] pointer substraction causes coredump with ftrapv on edge case

[baiwfg2 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110399

--- Comment #3 from Chan Lewis <baiwfg2 at gmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> Dup of bug 13421.
> 
> *** This bug has been marked as a duplicate of bug 13421 ***

I see. I wonder why gcc consider pointer signed and need to abort in this case,
whereas clang still works as expected. If we change pointer to unsigned in our
codebase, that will be lots of work.