[Bug c++/87289] jdk11 plinux compiled with gcc 7.3 doesn't work with NativeImageBuffer

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87289

Peter Bergner <bergner at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |bergner at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #8 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to pdbain from comment #5)
> The compiler trips on this part of jnicsup.cpp (ca. line 500):
> 
> #ifdef J9VM_INTERP_FLOAT_SUPPORT
> 			case 'F':
> 				/* float type */
> 				fltPtr = (jfloat*)--sp;
> 				/* The Linux SH4 compiler needs the next two lines to be two steps.  If
> you combine them it fails to compile */
> 				dbl = ARG(jdouble, f);
> 				*fltPtr = (jfloat)dbl;
> 				break;
> 			case 'D':
> 				/* double type */
> 				dbl = ARG(jdouble, d);
> 				lngOrDblPtr = (UDATA *) &dbl;
> 				goto pushLongOrDouble;
> #endif
> 			case 'J':
> 				/* long type */
> 				lng = ARG(jlong, j);
> 				lngOrDblPtr = (UDATA *) &lng;
> pushLongOrDouble:
> #ifdef J9VM_ENV_DATA64
> 				--sp;
> 				*--sp = *(lngOrDblPtr);
> #else
> 				*--sp = *(lngOrDblPtr + 1);
> 				*--sp = *(lngOrDblPtr);
> #endif
> 				break;

I was able to create a small reproducer program and it shows you have a
-fstrict-aliasing bug in your source code.  You take the address of the double
var "dbl" and cast its address to a UDATA * pointer and then use it.  That
violates aliasing rules.  I was able to get my small reproducer program to work
using the -fno-strict-aliasing option as well as using -O0 and -O1 where
-fstrict-aliasing is not enabled by default.

I'll note that a quick scan through pushArguments() shows other code that looks
to violate the aliasing rules too.  You can either use -fno-strict-aliasing as
a work around or you will need to fix your code.