os_dep.c

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        ABORT("Seek to object table failed");
    }
    for (nsegs = E32_OBJCNT(hdr386); nsegs > 0; nsegs--) {
      int flags;
      if (fread((char *)(&seg), 1, sizeof seg, myexefile) < sizeof seg) {
        GC_err_puts("Couldn't read obj table entry from ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Couldn't read obj table entry");
      }
      flags = O32_FLAGS(seg);
      if (!(flags & OBJWRITE)) continue;
      if (!(flags & OBJREAD)) continue;
      if (flags & OBJINVALID) {
          GC_err_printf("Object with invalid pages?\n");
          continue;
      } 
      GC_add_roots_inner(O32_BASE(seg), O32_BASE(seg)+O32_SIZE(seg), FALSE);
    }
}

# else /* !OS2 */

# if defined(MSWIN32) || defined(MSWINCE)

# ifdef MSWIN32
  /* Unfortunately, we have to handle win32s very differently from NT, 	*/
  /* Since VirtualQuery has very different semantics.  In particular,	*/
  /* under win32s a VirtualQuery call on an unmapped page returns an	*/
  /* invalid result.  Under NT, GC_register_data_segments is a noop and	*/
  /* all real work is done by GC_register_dynamic_libraries.  Under	*/
  /* win32s, we cannot find the data segments associated with dll's.	*/
  /* We register the main data segment here.				*/
  GC_bool GC_no_win32_dlls = FALSE;	 
  	/* This used to be set for gcc, to avoid dealing with		*/
  	/* the structured exception handling issues.  But we now have	*/
  	/* assembly code to do that right.				*/

# if defined(GWW_VDB)

#   ifndef _BASETSD_H_
      typedef ULONG * PULONG_PTR;
#   endif
    typedef UINT (WINAPI * GetWriteWatch_type)(
      DWORD, PVOID, SIZE_T, PVOID*, PULONG_PTR, PULONG);
    static GetWriteWatch_type GetWriteWatch_func;
    static DWORD GetWriteWatch_alloc_flag;

#   define GC_GWW_AVAILABLE() (GetWriteWatch_func != NULL)

    static void detect_GetWriteWatch(void)
    {
      static GC_bool done;
      if (done)
        return;

      GetWriteWatch_func = (GetWriteWatch_type)
        GetProcAddress(GetModuleHandle("kernel32.dll"), "GetWriteWatch");
      if (GetWriteWatch_func != NULL) {
        /* Also check whether VirtualAlloc accepts MEM_WRITE_WATCH,   */
        /* as some versions of kernel32.dll have one but not the      */
        /* other, making the feature completely broken.               */
        void * page = VirtualAlloc(NULL, GC_page_size,
                                    MEM_WRITE_WATCH | MEM_RESERVE,
                                    PAGE_READWRITE);
        if (page != NULL) {
          PVOID pages[16];
          ULONG_PTR count = 16;
          DWORD page_size;
          /* Check that it actually works.  In spite of some 		*/
	  /* documentation it actually seems to exist on W2K.		*/
	  /* This test may be unnecessary, but ...			*/
          if (GetWriteWatch_func(WRITE_WATCH_FLAG_RESET,
                                 page, GC_page_size,
                                 pages,
                                 &count,
                                 &page_size) != 0) {
            /* GetWriteWatch always fails. */
            GetWriteWatch_func = NULL;
          } else {
            GetWriteWatch_alloc_flag = MEM_WRITE_WATCH;
          }
          VirtualFree(page, GC_page_size, MEM_RELEASE);
        } else {
          /* GetWriteWatch will be useless. */
          GetWriteWatch_func = NULL;
        }
      }
      if (GC_print_stats) {
        if (GetWriteWatch_func == NULL) {
          GC_log_printf("Did not find a usable GetWriteWatch()\n");
        } else {
          GC_log_printf("Using GetWriteWatch()\n");
        }
      }
      done = TRUE;
    }

# endif /* GWW_VDB */

  GC_bool GC_wnt = FALSE;
         /* This is a Windows NT derivative, i.e. NT, W2K, XP or later.  */
  
  void GC_init_win32(void)
  {
    /* Set GC_wnt.							 */
    /* If we're running under win32s, assume that no DLLs will be loaded */
    /* I doubt anyone still runs win32s, but ...			 */
    DWORD v = GetVersion();
    GC_wnt = !(v & 0x80000000);
    GC_no_win32_dlls |= ((!GC_wnt) && (v & 0xff) <= 3);
  }

  /* Return the smallest address a such that VirtualQuery		*/
  /* returns correct results for all addresses between a and start.	*/
  /* Assumes VirtualQuery returns correct information for start.	*/
  ptr_t GC_least_described_address(ptr_t start)
  {  
    MEMORY_BASIC_INFORMATION buf;
    size_t result;
    LPVOID limit;
    ptr_t p;
    LPVOID q;
    
    limit = GC_sysinfo.lpMinimumApplicationAddress;
    p = (ptr_t)((word)start & ~(GC_page_size - 1));
    for (;;) {
    	q = (LPVOID)(p - GC_page_size);
    	if ((ptr_t)q > (ptr_t)p /* underflow */ || q < limit) break;
    	result = VirtualQuery(q, &buf, sizeof(buf));
    	if (result != sizeof(buf) || buf.AllocationBase == 0) break;
    	p = (ptr_t)(buf.AllocationBase);
    }
    return p;
  }
# endif

# ifndef REDIRECT_MALLOC
  /* We maintain a linked list of AllocationBase values that we know	*/
  /* correspond to malloc heap sections.  Currently this is only called */
  /* during a GC.  But there is some hope that for long running		*/
  /* programs we will eventually see most heap sections.		*/

  /* In the long run, it would be more reliable to occasionally walk 	*/
  /* the malloc heap with HeapWalk on the default heap.  But that	*/
  /* apparently works only for NT-based Windows. 			*/ 

  /* In the long run, a better data structure would also be nice ...	*/
  struct GC_malloc_heap_list {
    void * allocation_base;
    struct GC_malloc_heap_list *next;
  } *GC_malloc_heap_l = 0;

  /* Is p the base of one of the malloc heap sections we already know	*/
  /* about?								*/
  GC_bool GC_is_malloc_heap_base(ptr_t p)
  {
    struct GC_malloc_heap_list *q = GC_malloc_heap_l;

    while (0 != q) {
      if (q -> allocation_base == p) return TRUE;
      q = q -> next;
    }
    return FALSE;
  }

  void *GC_get_allocation_base(void *p)
  {
    MEMORY_BASIC_INFORMATION buf;
    size_t result = VirtualQuery(p, &buf, sizeof(buf));
    if (result != sizeof(buf)) {
      ABORT("Weird VirtualQuery result");
    }
    return buf.AllocationBase;
  }

  size_t GC_max_root_size = 100000;	/* Appr. largest root size.	*/

  void GC_add_current_malloc_heap()
  {
    struct GC_malloc_heap_list *new_l =
                 malloc(sizeof(struct GC_malloc_heap_list));
    void * candidate = GC_get_allocation_base(new_l);

    if (new_l == 0) return;
    if (GC_is_malloc_heap_base(candidate)) {
      /* Try a little harder to find malloc heap.			*/
	size_t req_size = 10000;
	do {
	  void *p = malloc(req_size);
	  if (0 == p) { free(new_l); return; }
 	  candidate = GC_get_allocation_base(p);
	  free(p);
	  req_size *= 2;
	} while (GC_is_malloc_heap_base(candidate)
	         && req_size < GC_max_root_size/10 && req_size < 500000);
	if (GC_is_malloc_heap_base(candidate)) {
	  free(new_l); return;
	}
    }
    if (GC_print_stats)
	  GC_log_printf("Found new system malloc AllocationBase at %p\n",
                        candidate);
    new_l -> allocation_base = candidate;
    new_l -> next = GC_malloc_heap_l;
    GC_malloc_heap_l = new_l;
  }
# endif /* REDIRECT_MALLOC */
  
  /* Is p the start of either the malloc heap, or of one of our */
  /* heap sections?						*/
  GC_bool GC_is_heap_base (ptr_t p)
  {
     
     unsigned i;
     
#    ifndef REDIRECT_MALLOC
       static word last_gc_no = (word)(-1);
     
       if (last_gc_no != GC_gc_no) {
	 GC_add_current_malloc_heap();
	 last_gc_no = GC_gc_no;
       }
       if (GC_root_size > GC_max_root_size) GC_max_root_size = GC_root_size;
       if (GC_is_malloc_heap_base(p)) return TRUE;
#    endif
     for (i = 0; i < GC_n_heap_bases; i++) {
         if (GC_heap_bases[i] == p) return TRUE;
     }
     return FALSE ;
  }

# ifdef MSWIN32
  void GC_register_root_section(ptr_t static_root)
  {
      MEMORY_BASIC_INFORMATION buf;
      size_t result;
      DWORD protect;
      LPVOID p;
      char * base;
      char * limit, * new_limit;
    
      if (!GC_no_win32_dlls) return;
      p = base = limit = GC_least_described_address(static_root);
      while (p < GC_sysinfo.lpMaximumApplicationAddress) {
        result = VirtualQuery(p, &buf, sizeof(buf));
        if (result != sizeof(buf) || buf.AllocationBase == 0
            || GC_is_heap_base(buf.AllocationBase)) break;
        new_limit = (char *)p + buf.RegionSize;
        protect = buf.Protect;
        if (buf.State == MEM_COMMIT
            && is_writable(protect)) {
            if ((char *)p == limit) {
                limit = new_limit;
            } else {
                if (base != limit) GC_add_roots_inner(base, limit, FALSE);
                base = p;
                limit = new_limit;
            }
        }
        if (p > (LPVOID)new_limit /* overflow */) break;
        p = (LPVOID)new_limit;
      }
      if (base != limit) GC_add_roots_inner(base, limit, FALSE);
  }
#endif
  
  void GC_register_data_segments()
  {
#     ifdef MSWIN32
      static char dummy;
      GC_register_root_section((ptr_t)(&dummy));
#     endif
  }

# else /* !OS2 && !Windows */

# if (defined(SVR4) || defined(AUX) || defined(DGUX) \
      || (defined(LINUX) && defined(SPARC))) && !defined(PCR)
ptr_t GC_SysVGetDataStart(size_t max_page_size, ptr_t etext_addr)
{
    word text_end = ((word)(etext_addr) + sizeof(word) - 1)
    		    & ~(sizeof(word) - 1);
    	/* etext rounded to word boundary	*/
    word next_page = ((text_end + (word)max_page_size - 1)
    		      & ~((word)max_page_size - 1));
    word page_offset = (text_end & ((word)max_page_size - 1));
    volatile char * result = (char *)(next_page + page_offset);
    /* Note that this isnt equivalent to just adding		*/
    /* max_page_size to &etext if &etext is at a page boundary	*/
    
    GC_setup_temporary_fault_handler();
    if (SETJMP(GC_jmp_buf) == 0) {
    	/* Try writing to the address.	*/
    	*result = *result;
        GC_reset_fault_handler();
    } else {
        GC_reset_fault_handler();
    	/* We got here via a longjmp.  The address is not readable.	*/
    	/* This is known to happen under Solaris 2.4 + gcc, which place	*/
    	/* string constants in the text segment, but after etext.	*/
    	/* Use plan B.  Note that we now know there is a gap between	*/
    	/* text and data segments, so plan A bought us something.	*/
    	result = (char *)GC_find_limit((ptr_t)(DATAEND), FALSE);
    }
    return((ptr_t)result);
}
# endif

# if defined(FREEBSD) && (defined(I386) || defined(X86_64) || defined(powerpc) || defined(__powerpc__)) && !defined(PCR)
/* Its unclear whether this should be identical to the above, or 	*/
/* whether it should apply to non-X86 architectures.			*/
/* For now we don't assume that there is always an empty page after	*/
/* etext.  But in some cases there actually seems to be slightly more.  */
/* This also deals with holes between read-only data and writable data.	*/
ptr_t GC_FreeBSDGetDataStart(size_t max_page_size, ptr_t etext_addr)
{
    word text_end = ((word)(etext_addr) + sizeof(word) - 1)
		     & ~(sizeof(word) - 1);
	/* etext rounded to word boundary	*/
    volatile word next_page = (text_end + (word)max_page_size - 1)
			      & ~((word)max_page_size - 1);
    volatile ptr_t result = (ptr_t)text_end;
    GC_setup_temporary_fault_handler();
    if (SETJMP(GC_jmp_buf) == 0) {
	/* Try reading at the address.				*/
	/* This should happen before there is another thread.	*/
	for (; next_page < (word)(DATAEND); next_page += (word)max_page_size)
	    *(volatile char *)next_page;
	GC_reset_fault_handler();
    } else {
	GC_reset_fault_handler();
	/* As above, we go to plan B	*/
	result = GC_find_limit((ptr_t)(DATAEND), FALSE);
    }
    return(result);
}

# endif


#ifdef AMIGA

#  define GC_AMIGA_DS
#  include "AmigaOS.c"
#  undef GC_AMIGA_DS

#else /* !OS2 && !Windows && !AMIGA */

void GC_register_data_segments(void)
{
#   if !defined(PCR) && !defined(MACOS)
#     if defined(REDIRECT_MALLOC) && defined(GC_SOLARIS_THREADS)
	/* As of Solaris 2.3, the Solaris threads implementation	*/
	/* allocates the data structure for the initial thread with	*/
	/* sbrk at process startup.  It needs to be scanned, so that	*/
	/* we don't lose some malloc allocated data structures		*/
	/* hanging from it.  We're on thin ice here ...			*/
        extern caddr_t sbrk();

	GC_add_roots_inner(DATASTART, (ptr_t)sbrk(0), FALSE);
#     else
	GC_add_roots_inner(DATASTART, (ptr_t)(DATAEND), FALSE);
#       if defined(DATASTART2)
          GC_add_roots_inner(DATASTART2, (ptr_t)(DATAEND2), FALSE);
#       endif
#     endif
#   endif
#   if defined(MACOS)
    {
#   if defined(THINK_C)
	extern void* GC_MacGetDataStart(void);
	/* globals begin above stack and end at a5. */
	GC_add_roots_inner((ptr_t)GC_MacGetDataStart(),
			   (ptr_t)LMGetCurrentA5(), FALSE);
#   else
#     if defined(__MWERKS__)
#       if !__POWERPC__
	  extern void* GC_MacGetDataStart(void);
	  /* MATTHEW: Function to handle Far Globals (CW Pro 3) */
#         if __option(far_data)
	  extern void* GC_MacGetDataEnd(void);
#         endif
	  /* globals begin above stack and end at a5. */
	  GC_add_roots_inner((ptr_t)GC_MacGetDataStart(),
          		     (ptr_t)LMGetCurrentA5(), FALSE);
	  /* MATTHEW: Handle Far Globals */          		     
#         if __option(far_data)
      /* Far globals follow he QD globals: */
	  GC_add_roots_inner((ptr_t)LMGetCurrentA5(),
          		     (ptr_t)GC_MacGetDataEnd(), FALSE);
#         endif
#       else
	  extern char __data_start__[], __data_end__[];
	  GC_add_roots_inner((ptr_t)&__data_start__,
	  		     (ptr_t)&__data_end__, FALSE);
#       endif /* __POWERPC__ */
#     endif /* __MWERKS__ */
#   endif /* !THINK_C */
    }
#   endif /* MACOS */

    /* Dynamic libraries are added at every collection, since they may  */
    /* change.								*/
}

# endif  /* ! AMIGA */
# endif  /* ! MSWIN32 && ! MSWINCE*/
# endif  /* ! OS2 */

/*
 * Auxiliary routines for obtaining memory from OS.
 */

# if !defined(OS2) && !defined(PCR) && !defined(AMIGA) \
	&& !defined(MSWIN32) && !defined(MSWINCE) \
	&& !defined(MACOS) && !defined(DOS4GW) && !defined(NONSTOP)

# define SBRK_ARG_T ptrdiff_t

#if defined(MMAP_SUPPORTED)

#ifdef USE_MMAP_FIXED
#   define GC_MMAP_FLAGS MAP_FIXED | MAP_PRIVATE
	/* Seems to yield better performance on Solaris 2, but can	*/
	/* be unreliable if something is already mapped at the address.	*/
#else
#   define GC_MMAP_FLAGS MAP_PRIVATE
#endif

#ifdef USE_MMAP_ANON
# define zero_fd -1
# if defined(MAP_ANONYMOUS)
#   define OPT_MAP_ANON MAP_ANONYMOUS
# else
#   define OPT_MAP_ANON MAP_ANON
# endif
#else
  static int zero_fd;