[Bug libc/2251] New: Weak undefined symbol doesn't work properly with PIE

[Bug libc/2251] New: Weak undefined symbol doesn't work properly with PIE

[hjl at lucon dot org]

Weak undefined symbol doesn't work proper with PIE. I see it on x86, x86-64
and IPF. See

http://gcc.gnu.org/ml/gcc/2006-01/msg01007.html

The bug is in both ld.so and ld. I opened a ld bug, PR 2218.

-- 
           Summary: Weak undefined symbol doesn't work properly with PIE
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: hjl at lucon dot org
                CC: glibc-bugs at sources dot redhat dot com
 BugsThisDependsOn: 2218


http://sourceware.org/bugzilla/show_bug.cgi?id=2251

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[Bug libc/2251] Weak undefined symbol doesn't work properly with PIE

[hjl at lucon dot org]

------- Additional Comments From hjl at lucon dot org  2006-01-31 19:17 -------
Created an attachment (id=854)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=854&action=view)
A testcase

PIE built with the fixed linker, I got

gcc -B./ -c -fPIC -g bar.c
gcc -B./ -shared -o libbar.so bar.o #-z nocombreloc
gcc -B./ -c -fPIC -g foo.c
gcc -B./ -c -fPIC -g main.c
gcc -B./ -c -fPIC -g dummy.c
gcc -B./ -shared -o libdummy.so dummy.o #-z nocombreloc
gcc -B./ -pie -o pie foo.o main.o libdummy.so -Wl,-z,nocombreloc -Wl,-rpath,.
gcc -B./ -o exec foo.o main.o libdummy.so -Wl,-z,nocombreloc -Wl,-rpath,.
cp -af libbar.so libdummy.so
./exec
main
foo
PASSED
./pie
main
foo
FAILED

That is undefined weak symbol in PIE is resolved to a definition in
libdummy.so unlike the normal executable.

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=2251

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[Bug libc/2251] Weak undefined symbol doesn't work properly with PIE

[hjl at lucon dot org]

------- Additional Comments From hjl at lucon dot org  2006-01-31 19:40 -------
A patch is posted at

http://sources.redhat.com/ml/libc-alpha/2006-01/msg00152.html

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=2251

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[Bug libc/2251] Weak undefined symbol doesn't work properly with PIE

[vapier at gentoo dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  GCC build triplet|                            |toolchain@gentoo.org


http://sourceware.org/bugzilla/show_bug.cgi?id=2251

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[Bug libc/2251] Weak undefined symbol doesn't work properly with PIE

[vapier at gentoo dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |toolchain at gentoo dot org
  GCC build triplet|toolchain@gentoo.org        |


http://sourceware.org/bugzilla/show_bug.cgi?id=2251

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[Bug libc/2251] Weak undefined symbol doesn't work properly with PIE

[bje at sources dot redhat dot com]

-- 
Bug 2251 depends on bug 2218, which changed state.

Bug 2218 Summary: Weak undefined symbol doesn't work properly with PIE
http://sourceware.org/bugzilla/show_bug.cgi?id=2218

           What    |Old Value                   |New Value
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

http://sourceware.org/bugzilla/show_bug.cgi?id=2251

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[Bug libc/2251] Weak undefined symbol doesn't work properly with PIE

[drepper at redhat dot com]

------- Additional Comments From drepper at redhat dot com  2006-08-09 06:07 -------
I completely disagree.

The main executable references undef_func.  It's not available at link time. 
That's fine, it's a weak reference.  Like every other weak reference every user
has to check whether the pointer is NULL or not.

But the fact that the symbol is not defined doesn't mean it should not be found
at runtime.  It should be treated like every other symbol not found in the
executable itself (sans the error message from the linker).

This means, the correct behavior is for the linker to emit a relocation for the
symbol in which case the exec test case would also print FAILED.  This is a bug
in binutils.

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


http://sourceware.org/bugzilla/show_bug.cgi?id=2251

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