[Bug c++/109389] New: g++ file.cpp -lgmp (option only works after filename)

[Bug c++/109389] New: g++ file.cpp -lgmp (option only works after filename)

[frechbengel at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109389

            Bug ID: 109389
           Summary: g++ file.cpp -lgmp (option only works after filename)
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: frechbengel at gmx dot de
  Target Milestone: ---

Hello,

1. »g++ --version« outputs:
g++ (Debian 10.2.1-6) 10.2.1 20210110


2. »g++ --help« says:
Usage: g++ [options] file...


3. But if I try to compile:

#include <gmp.h>
int main(){
mpz_t n;
mpz_init(n);
mpz_clear(n);
return 0;}


4. with »g++ -lgmp file.cpp« the error is:

/usr/bin/ld: /tmp/cc8lgHAc.o: in function `main':
guard_driver.cpp:(.text+0x10): undefined reference to `__gmpz_init'
/usr/bin/ld: guard_driver.cpp:(.text+0x21): undefined reference to
`__gmpz_set_ui'
/usr/bin/ld: guard_driver.cpp:(.text+0x34): undefined reference to
`operator<<(std::ostream&, __mpz_struct const*)'
/usr/bin/ld: guard_driver.cpp:(.text+0x55): undefined reference to
`__gmpz_clear'
collect2: error: ld returned 1 exit status


5. There is no error if I compile with:

»g++ file.cpp -lgmp«


6. As the --help says the options should be given BEFORE the filename it is a
feature if it works with options given after the filename, too. But I is
propably a bug that compilation only works with the option given after the
filename.

Regards and thank you for you valuable work
Bernd

[Bug c++/109389] g++ file.cpp -lgmp (option only works after filename)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109389

Jonathan Wakely <redi at gcc dot gnu.org> changed:

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

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Firstly, this is a proeprty of your linker, which is not part of GCC. GCC just
passes the arguments to the linker in the order you give them.

Secondly, this is not a bug, it's the expected behaviour for the linker.
https://c-faq.com/lib/libsearch.html

[Bug c++/109389] g++ file.cpp -lgmp (option only works after filename)

[frechbengel at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109389

--- Comment #2 from Bernd <frechbengel at gmx dot de> ---
@ Jonathan Wakely

Thank you for correcting me and setting the issue solved.

Sorry for the wrong report. For a long time g++ accepted the -lgmp before the
filename, clang++ still does. That's why I thought that this must a bug.

[Bug c++/109389] g++ file.cpp -lgmp (option only works after filename)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109389

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
It accepts it, but it does something different from when it is after the
objects.

[Bug c++/109389] g++ file.cpp -lgmp (option only works after filename)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109389

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Clang is not a linker either. Both Clang and GCC just pass the options to the
linker.

Any difference in behaviour is a difference in the linker, not a difference
between Clang and GCC.

[Bug c++/109389] g++ file.cpp -lgmp (option only works after filename)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109389

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note for shared libraries it might the case the gcc you using defaults to
passing  --as-needed to the linker and the clang driver does not.

[Bug c++/109389] g++ file.cpp -lgmp (option only works after filename)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109389

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note Debian (and Ubuntu) has a patch to their GCC which does cause the default
arguments to ld to include --as-needed . That is why you are seeing a
difference between gcc and clang. Note if you build GCC from source, you would
not have seen a difference here. Also note this is not a bug in GCC nor in
debian's gcc; just you misunderstanding the how linking works too.