[PATCH] fix KJS crash on some more strict platforms

[Helge Deller]

Some platforms are pretty strict about the alignment for some types
of variables.

Code like this (taken from kdelibs/kjs/internal.cpp):
const unsigned char NaN_Bytes[] = { 0x7f, 0xf8, 0, 0, 0, 0, 0, 0 };
....
double x = * (double*) NaN_Bytes;

e.g. gives the compiler warning message:
/home/cvs/kde20/kdelibs/kjs/internal.cpp:75: warning: cast from `const unsigned
   char*' to `const double*' increases required alignment of target type

and in this case KJS breaks with a SIGSEG fault if NaN_Bytes[] wasn't aligned by the
compiler to a 8 byte boundary. I my case the compiler (gcc on the HP PARISC platform)
aligned the NaN_Bytes arry by default to 4 bytes (which is normally OK) but
which of course by pure luck sometimes worked and sometimes just crashed.

The attached patch fixes this bug by using gcc's __aligned__ attribute if the sources
are built with g++. I assume other architectures (e.g. SPARC?) with other
compilers (e.g. aCC on HP/UX?) might want a similiar patch too, just to be on
the safe side. Adding a warning to the #else part in this case would IMHO be 
a good idea (Opinions?).

I would like to fix this bug now, so I would like to ask if it's Ok to submit this 
version of the patch to HEAD and backport it to KDE 3.1 ?

Helge
-------------- next part --------------
Index: internal.cpp
===================================================================
RCS file: /home/kde/kdelibs/kjs/internal.cpp,v
retrieving revision 1.170
diff -u -p -r1.170 internal.cpp
--- internal.cpp	17 Nov 2003 00:48:40 -0000	1.170
+++ internal.cpp	16 Dec 2003 20:54:05 -0000
@@ -54,16 +54,22 @@ extern int kjsyyparse();
 
 using namespace KJS;
 
+#if defined(__GNUC__)
+#define KJS_DOUBLE_ALIGN	__attribute__((__aligned__(sizeof(double))))
+#else
+#define KJS_DOUBLE_ALIGN
+#endif
+
 namespace KJS {
 #ifdef WORDS_BIGENDIAN
-  const unsigned char NaN_Bytes[] = { 0x7f, 0xf8, 0, 0, 0, 0, 0, 0 };
-  const unsigned char Inf_Bytes[] = { 0x7f, 0xf0, 0, 0, 0, 0, 0, 0 };
+  const unsigned char KJS_DOUBLE_ALIGN NaN_Bytes[] = { 0x7f, 0xf8, 0, 0, 0, 0, 0, 0 };
+  const unsigned char KJS_DOUBLE_ALIGN Inf_Bytes[] = { 0x7f, 0xf0, 0, 0, 0, 0, 0, 0 } ;
 #elif defined(arm)
-  const unsigned char NaN_Bytes[] = { 0, 0, 0xf8, 0x7f, 0, 0, 0, 0 };
-  const unsigned char Inf_Bytes[] = { 0, 0, 0xf0, 0x7f, 0, 0, 0, 0 };
+  const unsigned char KJS_DOUBLE_ALIGN NaN_Bytes[] = { 0, 0, 0xf8, 0x7f, 0, 0, 0, 0 } ;
+  const unsigned char KJS_DOUBLE_ALIGN Inf_Bytes[] = { 0, 0, 0xf0, 0x7f, 0, 0, 0, 0 } ;
 #else
-  const unsigned char NaN_Bytes[] = { 0, 0, 0, 0, 0, 0, 0xf8, 0x7f };
-  const unsigned char Inf_Bytes[] = { 0, 0, 0, 0, 0, 0, 0xf0, 0x7f };
+  const unsigned char KJS_DOUBLE_ALIGN NaN_Bytes[] = { 0, 0, 0, 0, 0, 0, 0xf8, 0x7f } ;
+  const unsigned char KJS_DOUBLE_ALIGN Inf_Bytes[] = { 0, 0, 0, 0, 0, 0, 0xf0, 0x7f } ;
 #endif
 
   const double NaN = *(const double*) NaN_Bytes;