xref: /gem5/src/systemc/tests/systemc/bugs/stack_alignment/stack_alignment.cpp

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/*****************************************************************************

  stack_alignment.cpp -- This example shows the crash of an fxsave instruction
                         in the sc_thread stack environment, but not in the
                         original linux process stack, which is correctly
                         aligned on first function.

  Please note that this test probably runs OK on a faulty implementation in
  64-bit in general (depending on your libc implementation), but will crash
  for sure in 32-bit.

  Original Author: Eric Paire, STMicroelectronics

 *****************************************************************************/

/*****************************************************************************

  MODIFICATION LOG - modifiers, enter your name, affiliation, date and
  changes you are making here.

      Name, Affiliation, Date:
  Description of Modification:

 *****************************************************************************/

#include "systemc.h"

/*
 * This program exhibits a bug in the management by QT of the stack of each
 * SystemC process. At least on i686 & x86_64, GCC makes the assumption that
 * the stack is aligned on a 16-byte boundary on each C/C++ function entry.
 * This convention allows GCC to respects constraints of automatic (stack)
 * variable alignment, using the __attribute)__ ((align(X))) GCC extension.
 *
 * The X is known to be 16 for i686 & x86_64, as this is the largest alignment
 * required by instructions operands, actually used by fxsave instruction.
 *
 * The attached code shows up the problem by crashing when fxsave is executed
 * in a SystemC thread, and executing correctly the *same* code on the initial
 * process stack, as initialized by the libc runtime.
 *
 * This misbehavior does not occur systematically for x86_64 (no crash,
 * or crash difficult to reproduce with standard malloc()), but often does
 * with i686. Notice that the instruction with the right alignment is shown
 * when using the myfpxregs address which is aligned on 16-byte boundary.
 */

#if defined(__x86_64__)
#  define FXSAVE "fxsaveq"
#else
#  define FXSAVE "fxsave"
#endif

#if defined(__GNUC__)
#  define ALIGNED_ARRAY( Type, Name, Size, Align ) \
	  Type Name[Size] __attribute__((aligned(Align)))
#elif defined(_MSC_VER)
#  define ALIGNED_ARRAY( Type, Name, Size, Align ) \
      __declspec(align(Align)) Type Name[Size]
#endif

#if defined(__GNUC__) && ( defined(__x86_64__) || defined(__i386__) )
#  define ASM( Assembly ) __asm__ __volatile__( Assembly )
#else
#  define ASM( Assembly ) /* not implemented */
#endif

// Class
SC_MODULE(C)
{
public:
    SC_CTOR(C) {
        SC_THREAD(run);
    }
    void run(void)
    {
        ALIGNED_ARRAY( char, fpxregs64, 512+15, 16 );

        cout << "Inside C::run() " << endl;

        // manually enforce alignment (volatile to avoid optmizations)
        char * volatile myfpxregs = fpxregs64;
        while ((uintptr_t)myfpxregs & 0xF)
            myfpxregs++;

        // the "real" requirement: enforced alignment works
        sc_assert( !((uintptr_t)fpxregs64 & 0xF) );
        sc_assert( !((uintptr_t)myfpxregs & 0xF) );
        sc_assert( myfpxregs == fpxregs64 );

        // test assembly on supported platforms
        ASM( FXSAVE " (%0)" :: "r"(myfpxregs) );
        cout << "Between C::run() " << endl;
        ASM( FXSAVE " %0" : "=m"(fpxregs64) );

        cout << "Out of C::run() " << endl;
    }
};

int sc_main(int , char** ) {
  C the_C("C");

  ALIGNED_ARRAY( char, fpxregs64, 512, 16 );

  cout << "Inside sc_main() " << endl;
  ASM( FXSAVE " %0" : "=m"(fpxregs64) );
  sc_start(1, SC_NS);
  cout << "Out of sc_main() " << endl;
  return 0;
}