[Bug ld/10426] New: ld incorrectly creates STT_GNU_IFUNC SHN_UNDEF symbols

[jakub at redhat dot com]

See https://bugzilla.redhat.com/show_bug.cgi?id=512937
No SHN_UNDEF symbols should ever have STT_GNU_IFUNC type, they should be
STT_FUNC instead.  Whether a symbol in the shared library some other shared
library or binary is linked dynamically against is STT_GNU_IFUNC or not doesn't
say anything about whether it will be actually indirect or direct function call
at runtime.  IFUNC is always only a property of a symbol definition.
Especially for PLT SHN_UNDEF symbols with non-zero st_value this is fatal
problem, see e.g.
https://bugzilla.redhat.com/show_bug.cgi?id=512078

Testcase:
BINUTILS_OBJ=/usr/src/binutils/obj
BINUTILS_SRC=/usr/src/binutils
gcc  -B$BINUTILS_OBJ/ld/tmpdir/gas/ -I$BINUTILS_SRC/ld/testsuite/ld-ifunc -g
-O2 \
  -c -fPIC -DWITH_IFUNC -c $BINUTILS_SRC/ld/testsuite/ld-ifunc/lib.c \
  -o shared_ifunc.o
$BINUTILS_OBJ/ld/ld-new  -o libshared_ifunc.so -shared shared_ifunc.o 
echo 'extern int library_func2 (void);' > test.c
echo 'int main (void) { library_func2 (); return 0; }' >> test.c
gcc -B $BINUTILS_OBJ/ld/tmpdir/ld/ -o test test.c ./libshared_ifunc.so
$BINUTILS_OBJ/binutils/readelf -Ws test | grep IFUNC.*UND
echo 'extern int library_func2 (void);' > test2.c
echo 'int (*fn) (void) = library_func2;' >> test2.c
echo 'int main (void) { fn (); return 0; }' >> test2.c
gcc -B $BINUTILS_OBJ/ld/tmpdir/ld/ -o test2 test2.c ./libshared_ifunc.so
$BINUTILS_OBJ/binutils/readelf -Ws test2 | grep IFUNC.*UND

Should print nothing, prints:
     1: 0000000000000000     0 IFUNC   GLOBAL DEFAULT  UND library_func2
    49: 0000000000000000     0 IFUNC   GLOBAL DEFAULT  UND library_func2
     5: 0000000000400458     0 IFUNC   GLOBAL DEFAULT  UND library_func2
    49: 0000000000400458     0 IFUNC   GLOBAL DEFAULT  UND library_func2
with CVS trunk.

-- 
           Summary: ld incorrectly creates STT_GNU_IFUNC SHN_UNDEF symbols
           Product: binutils
           Version: 2.20 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
        AssignedTo: unassigned at sources dot redhat dot com
        ReportedBy: jakub at redhat dot com
                CC: bug-binutils at gnu dot org,hjl dot tools at gmail dot
                    com


http://sourceware.org/bugzilla/show_bug.cgi?id=10426

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