[Bug libgcj/50057] [4.7 regression] misalignment of java_exception_header resulted in throwable to be null

[jojelino at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50057

--- Comment #4 from gee <jojelino at gmail dot com> 2012-01-18 13:28:53 UTC ---
Created attachment 26365
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26365
proposed patch

it fixes invalid padding that caused the bug.

#include <cstddef>
#define DEBUG 1
#include <cassert>
#include <cstdlib>
#include <cstdio>
#include <iostream>
typedef int* jthrowable,_Unwind_Ptr;
struct alignment_test_struct
{
  char space;
  char end[0] __attribute__((aligned));
};

struct java_exception_header
{
#define MEMBER_AT_FRONT \
  _Unwind_Ptr* landingPad;\
  int handlerSwitchValue;
  MEMBER_AT_FRONT
  struct _pad{MEMBER_AT_FRONT};
#undef MEMBER_AT_FRONT

#define PADORZERO(x,y,z) (sizeof(x)<sizeof(y)?sizeof(y)-sizeof(x)+(z):0)
  char
pad[PADORZERO(jthrowable,alignment_test_struct,PADORZERO(_pad,alignment_test_struct,0))];
#undef PADORZERO
  jthrowable __attribute__((packed)) value;


  int* unwindHeader;
};

int main()
{

    alignment_test_struct s;
    java_exception_header t;
    printf("%x\n",sizeof(alignment_test_struct));
    int
dat[]={offsetof(java_exception_header,pad),sizeof(java_exception_header::pad)
              
,offsetof(java_exception_header,value),sizeof(java_exception_header::value)
              
,offsetof(java_exception_header,unwindHeader),sizeof(java_exception_header::unwindHeader)};

    printf("pad %x %x\n",dat[0],dat[1]);
    printf("value %x %x\n",dat[2],dat[3]);
    printf("header %x %x\n",dat[4],dat[5]);
    assert((dat[2]+dat[3])==dat[4]);
    return 0;
}

10
pad 8 14
value 1c 4
header 20 4