Bug#852091: gcc-6: Binaries compiled with gccgo on m68k crash (unaligned access)

[John Paul Adrian Glaubitz]

Source: gcc-6
Version: 6.3.0-3
Severity: normal
Tags: patch
User: debian-68k@lists.debian.org
Usertags: m68k

Hi!

The attached patch is a backport of the fix provided by upstream to fix
gccgo on m68k [1]. I have added this patch to gcc-6_6.3.0-3, rebuild the
package and verified gccgo now produces working binaries.

Of course, if upstream decides to backport this patch to gcc-6, it won't
be necessary to carry this patch in gcc-6. But in case that doesn't happen,
here's a patch verified to be working to be applied instantly.

Thanks,
Adrian

--
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaub...@debian.org
`. `'   Freie Universitaet Berlin - glaub...@physik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913

--- a/src/gcc/go/gofrontend/types.cc.orig       2016-02-03 07:54:41.000000000 
+0100
+++ b/src/gcc/go/gofrontend/types.cc    2017-01-20 17:54:46.460409688 +0100
@@ -2175,11 +2175,25 @@
       is_common = true;
     }
 
+  // The current garbage collector requires that the GC symbol be
+  // aligned to at least a four byte boundary.  See the use of PRECISE
+  // and LOOP in libgo/runtime/mgc0.c.
+  int64_t align;
+  if (!sym_init->type()->backend_type_align(gogo, &align))
+    go_assert(saw_errors());
+  if (align < 4)
+    align = 4;
+  else
+    {
+      // Use default alignment.
+      align = 0;
+    }
+
   // Since we are building the GC symbol in this package, we must create the
   // variable before converting the initializer to its backend representation
   // because the initializer may refer to the GC symbol for this type.
   this->gc_symbol_var_ =
-    gogo->backend()->implicit_variable(sym_name, sym_btype, false, true, 
is_common, 0);
+    gogo->backend()->implicit_variable(sym_name, sym_btype, false, true, 
is_common, align);
   if (phash != NULL)
     *phash = this->gc_symbol_var_;
 
--- a/src/libgo/runtime/go-unsafe-pointer.c.orig        2015-10-29 
19:14:50.000000000 +0100
+++ b/src/libgo/runtime/go-unsafe-pointer.c     2017-01-20 17:57:12.227392567 
+0100
@@ -36,7 +36,8 @@
   sizeof REFLECTION - 1
 };
 
-const uintptr unsafe_Pointer_gc[] = {sizeof(void*), GC_APTR, 0, GC_END};
+const uintptr unsafe_Pointer_gc[] __attribute__((aligned(4))) =
+  {sizeof(void*), GC_APTR, 0, GC_END};
 
 const struct __go_type_descriptor unsafe_Pointer =
 {
--- a/src/libgo/runtime/parfor.c.orig   2015-10-31 01:59:47.000000000 +0100
+++ b/src/libgo/runtime/parfor.c        2017-01-20 17:58:47.154729980 +0100
@@ -10,7 +10,7 @@
 struct ParForThread
 {
        // the thread's iteration space [32lsb, 32msb)
-       uint64 pos;
+       uint64 pos __attribute__((aligned(8)));
        // stats
        uint64 nsteal;
        uint64 nstealcnt;
--- a/src/libgo/runtime/runtime.h.orig  2016-02-12 23:10:09.000000000 +0100
+++ b/src/libgo/runtime/runtime.h       2017-01-21 00:58:07.386595035 +0100
@@ -431,7 +431,7 @@
                                        // otherwise parfor may return while 
other threads are still working
        ParForThread *thr;              // array of thread descriptors
        // stats
-       uint64 nsteal;
+       uint64 nsteal  __attribute__((aligned(8))); // force alignment for m68k
        uint64 nstealcnt;
        uint64 nprocyield;
        uint64 nosyield;