[Bug c/25380] New: application segmentation fault when compiled with "-O2", but not with "-O1"

[Bug c/25380] New: application segmentation fault when compiled with "-O2", but not with "-O1"

[hugh dot daschbach at emulex dot com]

ppc64 segmentation fault on function return that returns the value of another
function.

Segmentation fault occurs when application is compiled with "-O2", but not when
compiled with "-O1".  *.i files identical, so included is a small test program,
rather than the .i file.  Apply following as a patch.  Test with "make test".


diff -urpN null/libwrapped.c ppc-test/libwrapped.c
--- null/libwrapped.c 1969-12-31 16:00:00.000000000 -0800
+++ ppc-test/libwrapped.c 2005-12-12 10:22:02.000000000 -0800
@@ -0,0 +1,11 @@
+#include "proto.h"
+
+unsigned long fn(void)
+{
+   return 0;
+}
+
+unsigned long wrapped(void)
+{
+ return fn();
+}
diff -urpN null/main.c ppc-test/main.c
--- null/main.c 1969-12-31 16:00:00.000000000 -0800
+++ ppc-test/main.c 2005-12-12 12:11:37.000000000 -0800
@@ -0,0 +1,9 @@
+#include <stdio.h>
+#include "proto.h"
+
+int  main(int argc, char **argv)
+{
+ printf("unwrapped: %ld\n", fn());
+ printf("wrapped: %ld\n", wrapped());
+ return 0;
+}
diff -urpN null/Makefile ppc-test/Makefile
--- null/Makefile 1969-12-31 16:00:00.000000000 -0800
+++ ppc-test/Makefile 2005-12-12 12:27:25.000000000 -0800
@@ -0,0 +1,21 @@
+# -*- makefile -*-
+
+CFLAGS = -m64 -Wall -g -O2
+
+main: main.o libwrapped.so
+ $(CC) $(CFLAGS) -o main main.o -L. -lwrapped
+
+libwrapped.o: libwrapped.c proto.h
+ $(CC) $(CFLAGS) -c -o libwrapped.o libwrapped.c
+
+libwrapped.so: libwrapped.o
+ ld -g -m elf64ppc -G -h  libwrapped.so -o libwrapped.so libwrapped.o
+
+main.o: main.c proto.h
+ $(CC) $(CFLAGS) -c -o main.o main.c
+
+clean:
+ rm -f *.o *.so main
+
+test: main
+ LD_LIBRARY_PATH=. ./main
diff -urpN null/proto.h ppc-test/proto.h
--- null/proto.h 1969-12-31 16:00:00.000000000 -0800
+++ ppc-test/proto.h 2005-12-09 13:58:10.000000000 -0800
@@ -0,0 +1,3 @@
+extern unsigned long fn(void);
+extern unsigned long wrapped(void);
+


-- 
           Summary: application segmentation fault when compiled with "-O2",
                    but not with "-O1"
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hugh dot daschbach at emulex dot com
 GCC build triplet: powerpc64-unknown-linux-gnu
  GCC host triplet: powerpc64-unknown-linux-gnu
GCC target triplet: powerpc64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25380

[Bug c/25380] application segmentation fault when compiled with "-O2", but not with "-O1"

[hugh dot daschbach at emulex dot com]

------- Comment #1 from hugh dot daschbach at emulex dot com  2005-12-13 02:25 -------
Forgot version data: First seen on 3.4.4 20050721 (Red Hat 3.4.4-2).
Last tested: svn revision 108426.  Still fails.

Using built-in specs.
Target: powerpc64-unknown-linux-gnu
Configured with: ./configure
Thread model: posix
gcc version 4.2.0 20051212 (experimental)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25380

[Bug target/25380] application segmentation fault when compiled with "-O2", but not with "-O1"

[amodra at bigpond dot net dot au]

------- Comment #2 from amodra at bigpond dot net dot au  2005-12-13 04:28 -------
The testcase is invalid, because you are compiling libwrapped.so without -fPIC.
 Now, powerpc64 code is always PIC, so you might think that -fPIC (or -fpic) is
unnecessary on powerpc64 shared libraries.  However, -fPIC/pic also tells gcc
to compile assuming that the object might be for a shared library.  One thing
this affects is whether tail calls can be made to global functions.  At -O2,
sibling/tail call optimisation is done, so we get a tail call from "wrapped" to
"fn" because -fPIC wasn't specified.  This tail call inside the shared lib
destroys r2, the TOC pointer, and an invalid TOC access is the reason for the
segfault.

It might possible to do something about this in the linker, but more
complicated examples are not possible to fix.  eg. where the function
tail-called is overridden by a function of the same name in the main app.


-- 

amodra at bigpond dot net dot au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amodra at bigpond dot net
                   |                            |dot au
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25380