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* [Bug c/110399] New: pointer substraction causes coredump with ftrapv on edge case
@ 2023-06-25  1:49 baiwfg2 at gmail dot com
  2023-06-25  1:59 ` [Bug middle-end/110399] " pinskia at gcc dot gnu.org
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: baiwfg2 at gmail dot com @ 2023-06-25  1:49 UTC (permalink / raw)
  To: gcc-bugs

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.

^ permalink raw reply	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-06-29  9:33 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-06-25  1:49 [Bug c/110399] New: pointer substraction causes coredump with ftrapv on edge case baiwfg2 at gmail dot com
2023-06-25  1:59 ` [Bug middle-end/110399] " pinskia at gcc dot gnu.org
2023-06-25  2:01 ` pinskia at gcc dot gnu.org
2023-06-29  9:33 ` baiwfg2 at gmail dot com

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