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From: "vincent.riviere at freesbee dot fr" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/94815] New: Abusive -Wrestrict warning with sprintf
Date: Tue, 28 Apr 2020 11:56:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94815

            Bug ID: 94815
           Summary: Abusive -Wrestrict warning with sprintf
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincent.riviere at freesbee dot fr
  Target Milestone: ---
            Target: m68k-elf

Testcase:

$ cat foo.c && m68k-elf-gcc -c foo.c -Wall -O
char *strcpy(char *, const char *);
int sprintf(char *, const char *, ...);

char* myalloc(int n);

void f(void)
{
    char* buf =3D myalloc(20);
    char* str1 =3D buf;
    char* str2 =3D buf + 10;

    strcpy(str2, "123");
    sprintf(str1, "ABC%s", str2);
}
foo.c: In function 'f':
foo.c:13:5: warning: 'sprintf' argument 3 may overlap destination object 'b=
uf'
[-Wrestrict]
   13 |     sprintf(str1, "ABC%s", str2);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

This warning is a unexpected because:

1) strcpy() and sprintf() are declared without __restrict, but __restrict r=
ules
are still actually used.

2) In this simple example, it is obvious that the buffer will not overflow.

This is annoying, because it prevents creating several logical buffers from=
 a
single allocation.=