source: patches/grub-0.97-use_mmap-2.patch@ 6cd0ea5

grub/asmstub.c

@@ -42 +42 @@
 #include <sys/time.h>
 #include <termios.h>
 #include <signal.h>
+#include <sys/mman.h>
 
 #ifdef __linux__
 # include <sys/ioctl.h>         /* ioctl */
@@ -79 +80 @@
 struct apm_info apm_bios_info;
 
 /* Emulation requirements. */
-char *grub_scratch_mem = 0;
+void *grub_scratch_mem = 0;
 
 struct geometry *disks = 0;
 
@@ -103 +104 @@
 static unsigned int serial_speed;
 #endif /* SIMULATE_SLOWNESS_OF_SERIAL */
 
+/* This allocates page-aligned storage of the specified size, which must be
+ * a multiple of the page size as determined by calling sysconf(_SC_PAGESIZE)
+ */
+#ifdef __linux__
+static void *
+grub_mmap_alloc(size_t len)
+{
+  int mmap_flags = MAP_ANONYMOUS|MAP_PRIVATE;
+
+#ifdef MAP_32BIT
+  mmap_flags |= MAP_32BIT;
+#endif
+  /* Mark the simulated stack executable, as GCC uses stack trampolines
+   * to implement nested functions. */
+  return mmap(NULL, len, PROT_READ|PROT_WRITE|PROT_EXEC, mmap_flags, -1, 0);
+}
+#else /* !defined(__linux__) */
+static void *
+grub_mmap_alloc(size_t len)
+{
+  int fd = 0, offset = 0, ret = 0;
+  void *pa = MAP_FAILED; 
+  char template[] = "/tmp/grub_mmap_alloc_XXXXXX";
+  int e;
+
+  fd = mkstemp(template);
+  if (fd < 0)
+    return pa;
+
+  unlink(template);
+
+  ret = ftruncate(fd, len);
+  if (ret < 0)
+    return pa;
+
+  /* Mark the simulated stack executable, as GCC uses stack trampolines
+   * to implement nested functions. */
+  pa = mmap(NULL, len, PROT_READ|PROT_WRITE|PROT_EXEC,
+                  MAP_PRIVATE, fd, offset);
+
+  e = errno;
+  close(fd);
+  errno = e;
+  return pa;
+}
+#endif /* defined(__linux__) */
+
 /* The main entry point into this mess. */
 int
 grub_stage2 (void)
 {
   /* These need to be static, because they survive our stack transitions. */
   static int status = 0;
-  static char *realstack;
-  char *scratch, *simstack;
+  static void *realstack;
+  void *simstack_alloc_base, *simstack;
+  size_t simstack_size, page_size;
   int i;
 
   auto void doit (void);
@@ -142 +191 @@
     }
 
   assert (grub_scratch_mem == 0);
-  scratch = malloc (0x100000 + EXTENDED_MEMSIZE + 15);
-  assert (scratch);
-  grub_scratch_mem = (char *) ((((int) scratch) >> 4) << 4);
+
+  /* Allocate enough pages for 0x100000 + EXTENDED_SIZE + 15, and
+   * make sure the memory is aligned to a multiple of the system's
+   * page size */
+  page_size = sysconf (_SC_PAGESIZE);
+  simstack_size = ( 0x100000 + EXTENDED_MEMSIZE + 15);
+  if (simstack_size % page_size)
+    {
+      /* If we're not on a page_size boundary, round up to the next one */
+      simstack_size &= ~(page_size-1);
+      simstack_size += page_size;
+    }
+
+  /* Add one for a PROT_NONE boundary page at each end. */
+  simstack_size += 2 * page_size;
+
+  simstack_alloc_base = grub_mmap_alloc(simstack_size);
+  assert (simstack_alloc_base != MAP_FAILED);
+
+  /* mark pages above and below our simstack area as innaccessable.
+   * If the implementation we're using doesn't support that, then the
+   * new protection modes are undefined.  It's safe to just ignore
+   * them, though.  It'd be nice if we knew that we'd get a SEGV for
+   * touching the area, but that's all.  it'd be nice to have. */
+  mprotect (simstack_alloc_base, page_size, PROT_NONE);
+  mprotect ((void *)((unsigned long)simstack_alloc_base +
+                         simstack_size - page_size),  page_size, PROT_NONE);
+
+  grub_scratch_mem = (void *)((unsigned long)simstack_alloc_base + page_size);
 
   /* FIXME: simulate the memory holes using mprot, if available. */
 
@@ -217 +292 @@
   device_map = 0;
   free (disks);
   disks = 0;
-  free (scratch);
+  munmap(simstack_alloc_base, simstack_size);
   grub_scratch_mem = 0;
 
   if (serial_device)

stage2/builtins.c

@@ -130 +130 @@
   grub_printf ("[%d,%d,%d]", sector, offset, length);
 }
 
-
 
+/* blocklist_read_helper nee disk_read_blocklist_func was a nested
+ * function, to which pointers were taken and exposed globally.  Even
+ * in the GNU-C nested functions extension, they have local linkage,
+ * and aren't guaranteed to be accessable *at all* outside of their 
+ * containing scope.
+ *
+ * Above and beyond all of that, the variables within blocklist_func_context
+ * are originally local variables, with local (not even static) linkage,
+ * from within blocklist_func.  These were each referenced by
+ * disk_read_blocklist_func, which is only called from other functions
+ * through a globally scoped pointer.
+ * 
+ * The documentation in GCC actually uses the words "all hell will break
+ * loose" to describe this scenario.
+ *
+ * Also, "start_sector" was also used uninitialized, but gcc doesn't warn
+ * about it (possibly because of the scoping madness?)
+ */
+   
+static struct {
+       int start_sector;
+       int num_sectors;
+       int num_entries;
+       int last_length;
+} blocklist_func_context = {
+       .start_sector = 0,
+       .num_sectors = 0,
+       .num_entries = 0,
+       .last_length = 0
+};
+
+/* Collect contiguous blocks into one entry as many as possible,
+   and print the blocklist notation on the screen.  */
+static void
+blocklist_read_helper (int sector, int offset, int length)
+{
+  int *start_sector = &blocklist_func_context.start_sector;
+  int *num_sectors = &blocklist_func_context.num_sectors;
+  int *num_entries = &blocklist_func_context.num_entries;
+  int *last_length = &blocklist_func_context.last_length;
+
+  if (*num_sectors > 0)
+  {
+    if (*start_sector + *num_sectors == sector
+      && offset == 0 && *last_length == SECTOR_SIZE)
+    {
+      *num_sectors++;
+      *last_length = length;
+      return;
+    }
+    else
+    {
+      if (*last_length == SECTOR_SIZE)
+        grub_printf ("%s%d+%d", *num_entries ? "," : "",
+          *start_sector - part_start, *num_sectors);
+      else if (*num_sectors > 1)
+        grub_printf ("%s%d+%d,%d[0-%d]", *num_entries ? "," : "",
+          *start_sector - part_start, *num_sectors-1,
+          *start_sector + *num_sectors-1 - part_start, 
+          *last_length);
+      else
+        grub_printf ("%s%d[0-%d]", *num_entries ? "," : "",
+          *start_sector - part_start, *last_length);
+      *num_entries++;
+      *num_sectors = 0;
+    }
+  }
+
+  if (offset > 0)
+  {
+    grub_printf("%s%d[%d-%d]", *num_entries ? "," : "",
+          sector-part_start, offset, offset+length);
+    *num_entries++;
+  }
+  else
+  {
+    *start_sector = sector;
+    *num_sectors = 1;
+    *last_length = length;
+  }
+}
+
 /* blocklist */
 static int
 blocklist_func (char *arg, int flags)
 {
   char *dummy = (char *) RAW_ADDR (0x100000);
-  int start_sector;
-  int num_sectors = 0;
-  int num_entries = 0;
-  int last_length = 0;
 
-  auto void disk_read_blocklist_func (int sector, int offset, int length);
-  
-  /* Collect contiguous blocks into one entry as many as possible,
-     and print the blocklist notation on the screen.  */
-  auto void disk_read_blocklist_func (int sector, int offset, int length)
-    {
-      if (num_sectors > 0)
-        {
-          if (start_sector + num_sectors == sector
-              && offset == 0 && last_length == SECTOR_SIZE)
-            {
-              num_sectors++;
-              last_length = length;
-              return;
-            }
-          else
-            {
-              if (last_length == SECTOR_SIZE)
-                grub_printf ("%s%d+%d", num_entries ? "," : "",
-                             start_sector - part_start, num_sectors);
-              else if (num_sectors > 1)
-                grub_printf ("%s%d+%d,%d[0-%d]", num_entries ? "," : "",
-                             start_sector - part_start, num_sectors-1,
-                             start_sector + num_sectors-1 - part_start, 
-                             last_length);
-              else
-                grub_printf ("%s%d[0-%d]", num_entries ? "," : "",
-                             start_sector - part_start, last_length);
-              num_entries++;
-              num_sectors = 0;
-            }
-        }
-
-      if (offset > 0)
-        {
-          grub_printf("%s%d[%d-%d]", num_entries ? "," : "",
-                      sector-part_start, offset, offset+length);
-          num_entries++;
-        }
-      else
-        {
-          start_sector = sector;
-          num_sectors = 1;
-          last_length = length;
-        }
-    }
+  int *start_sector = &blocklist_func_context.start_sector;
+  int *num_sectors = &blocklist_func_context.num_sectors;
+  int *num_entries = &blocklist_func_context.num_entries;
 
   /* Open the file.  */

stage2/shared.h

@@ -36 +36 @@
 
 /* Maybe redirect memory requests through grub_scratch_mem. */
 #ifdef GRUB_UTIL
-extern char *grub_scratch_mem;
-# define RAW_ADDR(x) ((x) + (int) grub_scratch_mem)
+extern void *grub_scratch_mem;
+# define RAW_ADDR(x) ((x) + (unsigned long) grub_scratch_mem)
 # define RAW_SEG(x) (RAW_ADDR ((x) << 4) >> 4)
 #else
 # define RAW_ADDR(x) (x)