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From: "vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug driver/99896] New: g++ drops -lc
Date: Sat, 03 Apr 2021 13:04:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99896

            Bug ID: 99896
           Summary: g++ drops -lc
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

[ Spinoff from gdb PR https://sourceware.org/bugzilla/show_bug.cgi?id=3D276=
81 . ]

Consider the following test-case, consisting of:
...
$ cat main.c=20
#include <assert.h>
#include <stddef.h>

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <regex.h>

extern void foo (void);

int
main (void)
{
  regex_t re;

  int res =3D regcomp (&re, "bla", 0);
  assert (res =3D=3D 0);

  int res2 =3D regexec (&re, "bla", 0, NULL, 0);
  assert (res2 =3D=3D 0);

  regoff_t res3 =3D re_search (&re, "bla", 3, 0, 3, NULL);
  assert (res3 =3D=3D 0);

  foo ();

  return 0;
}=20
...
and:
...
$ cat foo.c=20
#include <assert.h>
#include <stddef.h>

#include <pcre2posix.h>

extern void foo (void);

void
foo (void)
{
  regex_t re;

  int res =3D pcre2_regcomp (&re, "bla", 0);
  assert (res =3D=3D 0);

  int res2 =3D pcre2_regexec (&re, "bla", 0, NULL, 0);
  assert (res2 =3D=3D 0);
}
...

We can compile with gcc and run like this:
...
$ gcc main.c -lc foo.c -lpcre2-posix
$ ./a.out=20
$
...

likewise, with clang:
...
$ clang main.c -lc foo.c -lpcre2-posix
$ ./a.out=20
$=20
...

likewise, with clang++:
...
$ clang++ -x c++ main.c -lc foo.c -lpcre2-posix
$ ./a.out=20
$
...

but with g++:
...
$ g++ -x c++ main.c -lc foo.c -lpcre2-posix
$ ./a.out=20
Segmentation fault (core dumped)
$
...

Using -v, we can see what goes wrong.  With gcc, we have:
...
collect2 ... main.o -lc foo.o -lpcre2-posix ...
...

With g++, we have instead:
...
collect2 ... main.o foo.o -lpcre2-posix ...
...

Workaround: use -Wl:
...
$ g++ -x c++ main.c -Wl,-lc foo.c -lpcre2-posix
$ ./a.out=20
$
...=