* fileio.c: Fix bugs with large file offsets.

The previous code assumed that file offsets (off_t values) fit in
EMACS_INT variables, which is not true on typical 32-bit hosts.
The code messed up by falsely reporting buffer overflow in cases
such as (insert-file-contents "big" nil 1 2) into an empty buffer
when "big" contains more than 2**29 bytes, even though this
inserts just one byte and does not overflow the buffer.
(Finsert_file_contents): Store file offsets as off_t
values, not as EMACS_INT values.  Check for overflow when
converting between EMACS_INT and off_t.  When checking for
buffer overflow or for overlap, take the offsets into account.
Don't use EMACS_INT for small values where int suffices.
When checking for overlap, fix a typo: ZV was used where
ZV_BYTE was intended.
(Fwrite_region): Don't assume off_t fits into 'long'.
* buffer.h (struct buffer.modtime_size): Now off_t, not EMACS_INT.

1 files changed, 62 insertions, 30 deletions

diff --git a/src/fileio.c b/src/fileio.c
index 60ee35bb399..fe0fb593208 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3179,6 +3179,7 @@ variable `last-coding-system-used' to the coding system actually used.  */)
   EMACS_INT inserted = 0;
   int nochange = 0;
   register EMACS_INT how_much;
+  off_t beg_offset, end_offset;
   register EMACS_INT unprocessed;
   int count = SPECPDL_INDEX ();
   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4, gcpro5;
@@ -3284,15 +3285,6 @@ variable `last-coding-system-used' to the coding system actually used.  */)
   record_unwind_protect (close_file_unwind, make_number (fd));
 
 
-  /* Check whether the size is too large or negative, which can happen on a
-     platform that allows file sizes greater than the maximum off_t value.  */
-  if (! not_regular
-      && ! (0 <= st.st_size && st.st_size <= BUF_BYTES_MAX))
-    buffer_overflow ();
-
-  /* Prevent redisplay optimizations.  */
-  current_buffer->clip_changed = 1;
-
   if (!NILP (visit))
     {
       if (!NILP (beg) || !NILP (end))
@@ -3302,26 +3294,64 @@ variable `last-coding-system-used' to the coding system actually used.  */)
     }
 
   if (!NILP (beg))
-    CHECK_NUMBER (beg);
+    {
+      if (! (RANGED_INTEGERP (0, beg, TYPE_MAXIMUM (off_t))))
+        wrong_type_argument (intern ("file-offset"), beg);
+      beg_offset = XFASTINT (beg);
+    }
   else
-    XSETFASTINT (beg, 0);
+    beg_offset = 0;
 
   if (!NILP (end))
-    CHECK_NUMBER (end);
+    {
+      if (! (RANGED_INTEGERP (0, end, TYPE_MAXIMUM (off_t))))
+        wrong_type_argument (intern ("file-offset"), end);
+      end_offset = XFASTINT (end);
+    }
   else
     {
-      if (! not_regular)
+      if (not_regular)
+        end_offset = TYPE_MAXIMUM (off_t);
+      else
         {
-          XSETINT (end, st.st_size);
+          end_offset = st.st_size;
+
+          /* A negative size can happen on a platform that allows file
+             sizes greater than the maximum off_t value.  */
+          if (end_offset < 0)
+            buffer_overflow ();
 
           /* The file size returned from stat may be zero, but data
              may be readable nonetheless, for example when this is a
              file in the /proc filesystem.  */
-          if (st.st_size == 0)
-            XSETINT (end, READ_BUF_SIZE);
+          if (end_offset == 0)
+            end_offset = READ_BUF_SIZE;
         }
     }
 
+  /* Check now whether the buffer will become too large,
+     in the likely case where the file's length is not changing.
+     This saves a lot of needless work before a buffer overflow.  */
+  if (! not_regular)
+    {
+      /* The likely offset where we will stop reading.  We could read
+         more (or less), if the file grows (or shrinks) as we read it.  */
+      off_t likely_end = min (end_offset, st.st_size);
+
+      if (beg_offset < likely_end)
+        {
+          ptrdiff_t buf_bytes =
+            Z_BYTE - (!NILP (replace) ? ZV_BYTE - BEGV_BYTE  : 0);
+          ptrdiff_t buf_growth_max = BUF_BYTES_MAX - buf_bytes;
+          off_t likely_growth = likely_end - beg_offset;
+          if (buf_growth_max < likely_growth)
+            buffer_overflow ();
+        }
+    }
+
+  /* Prevent redisplay optimizations.  */
+  current_buffer->clip_changed = 1;
+
   if (EQ (Vcoding_system_for_read, Qauto_save_coding))
     {
       coding_system = coding_inherit_eol_type (Qutf_8_emacs, Qunix);
@@ -3465,9 +3495,9 @@ variable `last-coding-system-used' to the coding system actually used.  */)
          give up on handling REPLACE in the optimized way.  */
       int giveup_match_end = 0;
 
-      if (XINT (beg) != 0)
+      if (beg_offset != 0)
         {
-          if (emacs_lseek (fd, XINT (beg), SEEK_SET) < 0)
+          if (lseek (fd, beg_offset, SEEK_SET) < 0)
             report_file_error ("Setting file position",
                                Fcons (orig_filename, Qnil));
         }
@@ -3515,7 +3545,7 @@ variable `last-coding-system-used' to the coding system actually used.  */)
       immediate_quit = 0;
       /* If the file matches the buffer completely,
          there's no need to replace anything.  */
-      if (same_at_start - BEGV_BYTE == XINT (end))
+      if (same_at_start - BEGV_BYTE == end_offset)
         {
           emacs_close (fd);
           specpdl_ptr--;
@@ -3530,16 +3560,17 @@ variable `last-coding-system-used' to the coding system actually used.  */)
          already found that decoding is necessary, don't waste time.  */
       while (!giveup_match_end)
         {
-          EMACS_INT total_read, nread, bufpos, curpos, trial;
+          int total_read, nread, bufpos, trial;
+          off_t curpos;
 
           /* At what file position are we now scanning?  */
-          curpos = XINT (end) - (ZV_BYTE - same_at_end);
+          curpos = end_offset - (ZV_BYTE - same_at_end);
           /* If the entire file matches the buffer tail, stop the scan.  */
           if (curpos == 0)
             break;
           /* How much can we scan in the next step?  */
           trial = min (curpos, sizeof buffer);
-          if (emacs_lseek (fd, curpos - trial, SEEK_SET) < 0)
+          if (lseek (fd, curpos - trial, SEEK_SET) < 0)
             report_file_error ("Setting file position",
                                Fcons (orig_filename, Qnil));
 
@@ -3606,13 +3637,14 @@ variable `last-coding-system-used' to the coding system actually used.  */)
 
           /* Don't try to reuse the same piece of text twice.  */
           overlap = (same_at_start - BEGV_BYTE
-                     - (same_at_end + st.st_size - ZV));
+                     - (same_at_end
+                        + (! NILP (end) ? end_offset : st.st_size) - ZV_BYTE));
           if (overlap > 0)
             same_at_end += overlap;
 
           /* Arrange to read only the nonmatching middle part of the file.  */
-          XSETFASTINT (beg, XINT (beg) + (same_at_start - BEGV_BYTE));
-          XSETFASTINT (end, XINT (end) - (ZV_BYTE - same_at_end));
+          beg_offset += same_at_start - BEGV_BYTE;
+          end_offset -= ZV_BYTE - same_at_end;
 
           del_range_byte (same_at_start, same_at_end, 0);
           /* Insert from the file at the proper position.  */
@@ -3657,7 +3689,7 @@ variable `last-coding-system-used' to the coding system actually used.  */)
       /* First read the whole file, performing code conversion into
          CONVERSION_BUFFER.  */
 
-      if (emacs_lseek (fd, XINT (beg), SEEK_SET) < 0)
+      if (lseek (fd, beg_offset, SEEK_SET) < 0)
         report_file_error ("Setting file position",
                            Fcons (orig_filename, Qnil));
 
@@ -3824,7 +3856,7 @@ variable `last-coding-system-used' to the coding system actually used.  */)
     }
 
   if (! not_regular)
-    total = XINT (end) - XINT (beg);
+    total = end_offset - beg_offset;
   else
     /* For a special file, all we can do is guess.  */
     total = READ_BUF_SIZE;
@@ -3845,9 +3877,9 @@ variable `last-coding-system-used' to the coding system actually used.  */)
   if (GAP_SIZE < total)
     make_gap (total - GAP_SIZE);
 
-  if (XINT (beg) != 0 || !NILP (replace))
+  if (beg_offset != 0 || !NILP (replace))
     {
-      if (emacs_lseek (fd, XINT (beg), SEEK_SET) < 0)
+      if (lseek (fd, beg_offset, SEEK_SET) < 0)
         report_file_error ("Setting file position",
                            Fcons (orig_filename, Qnil));
     }
@@ -4576,7 +4608,7 @@ This calls `write-region-annotate-functions' at the start, and
 
   if (!NILP (append) && !NILP (Ffile_regular_p (filename)))
     {
-      long ret;
+      off_t ret;
 
       if (NUMBERP (append))
         ret = emacs_lseek (desc, XINT (append), SEEK_CUR);