x86: Check IFUNC definition in unrelocated executable [BZ #20019]

Calling an IFUNC function defined in unrelocated executable also leads to
segfault.  Issue a fatal error message when calling IFUNC function defined
in the unrelocated executable from a shared library.

On x86, ifuncmain6pie failed with:

[hjl@gnu-cfl-2 build-i686-linux]$ ./elf/ifuncmain6pie --direct
./elf/ifuncmain6pie: IFUNC symbol 'foo' referenced in '/export/build/gnu/tools-build/glibc-32bit/build-i686-linux/elf/ifuncmod6.so' is defined in the executable and creates an unsatisfiable circular dependency.
[hjl@gnu-cfl-2 build-i686-linux]$ readelf -rW elf/ifuncmod6.so | grep foo
00003ff4  00000706 R_386_GLOB_DAT         0000400c   foo_ptr
00003ff8  00000406 R_386_GLOB_DAT         00000000   foo
0000400c  00000401 R_386_32               00000000   foo
[hjl@gnu-cfl-2 build-i686-linux]$

Remove non-JUMP_SLOT relocations against foo in ifuncmod6.so, which
trigger the circular IFUNC dependency, and build ifuncmain6pie with
-Wl,-z,lazy.

(cherry picked from commits 6ea5b57afa5cdc9ce367d2b69a2cebfb273e4617
 and 7137d682ebfcb6db5dfc5f39724718699922f06c)

1 files changed, 4 insertions, 4 deletions

diff --git a/elf/ifuncmod6.c b/elf/ifuncmod6.c
index 2e16c1d06d..2f6d0715e6 100644
--- a/elf/ifuncmod6.c
+++ b/elf/ifuncmod6.c
@@ -4,7 +4,7 @@ extern int foo (void);
 
 typedef int (*foo_p) (void);
 
-foo_p foo_ptr = foo;
+extern foo_p foo_ptr;
 
 foo_p
 get_foo_p (void)
@@ -12,8 +12,8 @@ get_foo_p (void)
   return foo_ptr;
 }
 
-foo_p
-get_foo (void)
+int
+call_foo (void)
 {
-  return foo;
+  return foo ();
 }