Bug#442918: -fvisibility=hidden should not affect symbols declared with extern

["Török Edvin" <edwintorok@gmail.com>]

Package: gcc
Version: 4:4.2.1-6
Severity: normal

--- Please enter the report below this line. ---

If I use -fvisibility=hidden, I expect symbols declared with "extern"
not be affected by it, as per the manpage (gcc-4.2 in gcc-4.2-doc).

"extern declarations are not affected by -fvisibility, so a lot of
code can be recompiled with -fvisibility=hidden with no modifications"

Yet a very simple testcase shows that even symbols marked extern are affected.
Tested with gcc-4.2, and gcc-4.1.

$ cat dso.c
extern int symbol(int x);
extern int symbol(int x)
{
}

$ gcc -fPIC -DPIC -fvisibility=hidden -shared dso.c -o dso.so &&
readelf -a dso.so | grep symbol
    49: 00000000000004cc     9 FUNC    LOCAL  HIDDEN   11 symbol

If I link an application that uses that symbol, the link will fail,
since the symbol is local and hidden.

Adding __attribute__((visibility("default"))) works as expected
(producing a DEFAULT symbol).

Either the manpage, or the behaviour should be changed.

Fixing the manpage is for sure the easiest way, but affecting externs
symbols by visibility=hidden is nonsense, since those are suppposed to
be the API functions that you "export".

Its the only (standard) way I can mark a functions as a globally
visible API. Also programs using symbols declared as extern expect
(and for good reason) to be able to successfully link with a DSO
containing that symbol.

Alternatives described at http://gcc.gnu.org/wiki/Visibility work of
course, but they require code changes. Not at all the "recompile with
no modifications" advertised by the manpage.
I should have another
-fvisibility-hidden-make-extern-behave-the-way-its-supposed-to-be flag
if the behaviour for "extern" and -fvisibility=hidden is to stay the
same.

But if this is to be fixed in the behaviour, then it should be
backported to gcc-4.1 too IMHO.


--- System information. ---
Architecture: amd64
Kernel:       Linux 2.6.23-rc6-hrt1-gc87ce658-dirty

Debian Release: lenny/sid
  500 unstable        www.debian-multimedia.org
  500 unstable        ftp.iasi.roedu.net
  500 testing         ftp.iasi.roedu.net
  500 feisty          wine.budgetdedicated.com
  500 etch            debian.beryl-project.org
    1 experimental    ftp.iasi.roedu.net

--- Package information. ---
Depends           (Version) | Installed
===========================-+-===============
cpp          (>= 4:4.2.1-6) | 4:4.2.1-6
gcc-4.2        (>= 4.2.1-3) | 4.2.1-5