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Widen modiff counts to avoid wraparound

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Widen modification counts to at least 64 bits, to make
wraparound practically impossible.
* doc/lispref/buffers.texi (Buffer Modification):
Don’t say the modification-count can wrap around.
* src/buffer.c (Frestore_buffer_modified_p, Fbuffer_swap_text)
(modify_overlay):
* src/insdel.c (insert_1_both, insert_from_string_1)
(insert_from_gap, insert_from_buffer_1)
(adjust_after_replace, replace_range, replace_range_2)
(del_range_2, modify_text):
* src/textprop.c (modify_text_properties):
Use modiff_incr instead of incrementing	directly.
(Fbuffer_modified_tick, Fbuffer_chars_modified_tick):
Don’t assume modification counts fit into fixnums.
* src/buffer.h (struct buffer_text, struct buffer):
* src/cmds.c (internal_self_insert):
* src/fileio.c (Finsert_file_contents):
* src/indent.c (last_known_column_modified):
* src/keyboard.c (command_loop_1):
* src/marker.c (cached_modiff):
* src/syntax.c (find_start_modiff, parse_sexp_propertize)
(find_defun_start):
* src/window.h (struct window):
Use modiff_count for modification counts.
* src/editfns.c (Fsubst_char_in_region):
Copy instead of incrementing modification counts,
since integer overflow checking is not needed here.
* src/lisp.h (modiff_count): New type.
(modiff_incr, modiff_to_integer): New inline functions.
* src/pdumper.c (dump_buffer): Update hash.
This commit is contained in:
Paul Eggert 2019-01-31 10:29:50 -08:00
parent a68eee50eb
commit 05d2fc7170
15 changed files with 72 additions and 47 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
doc/lispref/buffers.texi
View file

@ -573,7 +573,6 @@ echo area; use @code{set-buffer-modified-p} (above) instead.
This function returns @var{buffer}'s modification-count. This is a
counter that increments every time the buffer is modified. If
@var{buffer} is @code{nil} (or omitted), the current buffer is used.
The counter can wrap around occasionally.
@end defun
@defun buffer-chars-modified-tick &optional buffer

25
src/buffer.c
View file

@ -1413,7 +1413,7 @@ state of the current buffer. Use with care. */)
/* If SAVE_MODIFF == auto_save_modified == MODIFF,
we can either decrease SAVE_MODIFF and auto_save_modified
or increase MODIFF. */
: MODIFF++);
: modiff_incr (&MODIFF));
return flag;
}
@ -1422,11 +1422,11 @@ DEFUN ("buffer-modified-tick", Fbuffer_modified_tick, Sbuffer_modified_tick,
0, 1, 0,
doc: /* Return BUFFER's tick counter, incremented for each change in text.
Each buffer has a tick counter which is incremented each time the
text in that buffer is changed. It wraps around occasionally.
No argument or nil as argument means use current buffer as BUFFER. */)
(register Lisp_Object buffer)
text in that buffer is changed. No argument or nil as argument means
use current buffer as BUFFER. */)
(Lisp_Object buffer)
{
return make_fixnum (BUF_MODIFF (decode_buffer (buffer)));
return modiff_to_integer (BUF_MODIFF (decode_buffer (buffer)));
}
DEFUN ("buffer-chars-modified-tick", Fbuffer_chars_modified_tick,
@ -1439,9 +1439,9 @@ values returned by two individual calls of `buffer-chars-modified-tick',
you can tell whether a character change occurred in that buffer in
between these calls. No argument or nil as argument means use current
buffer as BUFFER. */)
(register Lisp_Object buffer)
(Lisp_Object buffer)
{
return make_fixnum (BUF_CHARS_MODIFF (decode_buffer (buffer)));
return modiff_to_integer (BUF_CHARS_MODIFF (decode_buffer (buffer)));
}
DEFUN ("rename-buffer", Frename_buffer, Srename_buffer, 1, 2,
@ -2375,9 +2375,12 @@ results, see Info node `(elisp)Swapping Text'. */)
bset_point_before_scroll (current_buffer, Qnil);
bset_point_before_scroll (other_buffer, Qnil);
current_buffer->text->modiff++; other_buffer->text->modiff++;
current_buffer->text->chars_modiff++; other_buffer->text->chars_modiff++;
current_buffer->text->overlay_modiff++; other_buffer->text->overlay_modiff++;
modiff_incr (&current_buffer->text->modiff);
modiff_incr (&other_buffer->text->modiff);
modiff_incr (&current_buffer->text->chars_modiff);
modiff_incr (&other_buffer->text->chars_modiff);
modiff_incr (&current_buffer->text->overlay_modiff);
modiff_incr (&other_buffer->text->overlay_modiff);
current_buffer->text->beg_unchanged = current_buffer->text->gpt;
current_buffer->text->end_unchanged = current_buffer->text->gpt;
other_buffer->text->beg_unchanged = other_buffer->text->gpt;
@ -3913,7 +3916,7 @@ modify_overlay (struct buffer *buf, ptrdiff_t start, ptrdiff_t end)
bset_redisplay (buf);
++BUF_OVERLAY_MODIFF (buf);
modiff_incr (&BUF_OVERLAY_MODIFF (buf));
}
/* Remove OVERLAY from LIST. */

18
src/buffer.h
View file

@ -422,20 +422,20 @@ struct buffer_text
ptrdiff_t gpt_byte; /* Byte pos of gap in buffer. */
ptrdiff_t z_byte; /* Byte pos of end of buffer. */
ptrdiff_t gap_size; /* Size of buffer's gap. */
EMACS_INT modiff; /* This counts buffer-modification events
modiff_count modiff; /* This counts buffer-modification events
for this buffer. It is incremented for
each such event, and never otherwise
changed. */
EMACS_INT chars_modiff; /* This is modified with character change
modiff_count chars_modiff; /* This is modified with character change
events for this buffer. It is set to
modiff for each such event, and never
otherwise changed. */
EMACS_INT save_modiff; /* Previous value of modiff, as of last
modiff_count save_modiff; /* Previous value of modiff, as of last
time buffer visited or saved a file. */
EMACS_INT overlay_modiff; /* Counts modifications to overlays. */
modiff_count overlay_modiff; /* Counts modifications to overlays. */
EMACS_INT compact; /* Set to modiff each time when compact_buffer
modiff_count compact; /* Set to modiff each time when compact_buffer
is called for this buffer. */
/* Minimum value of GPT - BEG since last redisplay that finished. */
@ -446,12 +446,12 @@ struct buffer_text
/* MODIFF as of last redisplay that finished; if it matches MODIFF,
beg_unchanged and end_unchanged contain no useful information. */
EMACS_INT unchanged_modified;
modiff_count unchanged_modified;
/* BUF_OVERLAY_MODIFF of current buffer, as of last redisplay that
finished; if it matches BUF_OVERLAY_MODIFF, beg_unchanged and
end_unchanged contain no useful information. */
EMACS_INT overlay_unchanged_modified;
modiff_count overlay_unchanged_modified;
/* Properties of this buffer's text. */
INTERVAL intervals;
@ -812,11 +812,11 @@ struct buffer
off_t modtime_size;
/* The value of text->modiff at the last auto-save. */
EMACS_INT auto_save_modified;
modiff_count auto_save_modified;
/* The value of text->modiff at the last display error.
Redisplay of this buffer is inhibited until it changes again. */
EMACS_INT display_error_modiff;
modiff_count display_error_modiff;
/* The time at which we detected a failure to auto-save,
Or 0 if we didn't have a failure. */

2
src/cmds.c
View file

@ -423,7 +423,7 @@ internal_self_insert (int c, EMACS_INT n)
: UNIBYTE_TO_CHAR (XFIXNAT (Fprevious_char ())))
== Sword))
{
EMACS_INT modiff = MODIFF;
modiff_count modiff = MODIFF;
Lisp_Object sym;
sym = call0 (Qexpand_abbrev);

9
src/editfns.c
View file

@ -2291,10 +2291,11 @@ Both characters must have the same length of multi-byte form. */)
if (! NILP (noundo))
{
if (MODIFF - 1 == SAVE_MODIFF)
SAVE_MODIFF++;
if (MODIFF - 1 == BUF_AUTOSAVE_MODIFF (current_buffer))
BUF_AUTOSAVE_MODIFF (current_buffer)++;
modiff_count m = MODIFF;
if (SAVE_MODIFF == m - 1)
SAVE_MODIFF = m;
if (BUF_AUTOSAVE_MODIFF (current_buffer) == m - 1)
BUF_AUTOSAVE_MODIFF (current_buffer) = m;
}
/* The before-change-function may have moved the gap

4
src/fileio.c
View file

@ -4618,7 +4618,7 @@ by calling `format-decode', which see. */)
ptrdiff_t opoint = PT;
ptrdiff_t opoint_byte = PT_BYTE;
ptrdiff_t oinserted = ZV - BEGV;
EMACS_INT ochars_modiff = CHARS_MODIFF;
modiff_count ochars_modiff = CHARS_MODIFF;
TEMP_SET_PT_BOTH (BEGV, BEGV_BYTE);
insval = call3 (Qformat_decode,
@ -4658,7 +4658,7 @@ by calling `format-decode', which see. */)
ptrdiff_t opoint = PT;
ptrdiff_t opoint_byte = PT_BYTE;
ptrdiff_t oinserted = ZV - BEGV;
EMACS_INT ochars_modiff = CHARS_MODIFF;
modiff_count ochars_modiff = CHARS_MODIFF;
TEMP_SET_PT_BOTH (BEGV, BEGV_BYTE);
insval = call1 (XCAR (p), make_fixnum (oinserted));

2
src/indent.c
View file

@ -49,7 +49,7 @@ ptrdiff_t last_known_column_point;
/* Value of MODIFF when current_column was called. */
static EMACS_INT last_known_column_modified;
static modiff_count last_known_column_modified;
static ptrdiff_t current_column_1 (void);
static ptrdiff_t position_indentation (ptrdiff_t);

18
src/insdel.c
View file

@ -903,7 +903,7 @@ insert_1_both (const char *string,
the insertion. This, together with recording the insertion,
will add up to the right stuff in the undo list. */
record_insert (PT, nchars);
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
memcpy (GPT_ADDR, string, nbytes);
@ -1031,7 +1031,7 @@ insert_from_string_1 (Lisp_Object string, ptrdiff_t pos, ptrdiff_t pos_byte,
#endif
record_insert (PT, nchars);
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
GAP_SIZE -= outgoing_nbytes;
@ -1088,7 +1088,7 @@ insert_from_gap (ptrdiff_t nchars, ptrdiff_t nbytes, bool text_at_gap_tail)
of this dance. */
invalidate_buffer_caches (current_buffer, GPT, GPT);
record_insert (GPT, nchars);
MODIFF++;
modiff_incr (&MODIFF);
GAP_SIZE -= nbytes;
if (! text_at_gap_tail)
@ -1228,7 +1228,7 @@ insert_from_buffer_1 (struct buffer *buf,
#endif
record_insert (PT, nchars);
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
GAP_SIZE -= outgoing_nbytes;
@ -1329,7 +1329,7 @@ adjust_after_replace (ptrdiff_t from, ptrdiff_t from_byte,
if (len == 0)
evaporate_overlays (from);
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
}
@ -1524,7 +1524,7 @@ replace_range (ptrdiff_t from, ptrdiff_t to, Lisp_Object new,
check_markers ();
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
if (adjust_match_data)
@ -1655,7 +1655,7 @@ replace_range_2 (ptrdiff_t from, ptrdiff_t from_byte,
check_markers ();
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
}
@ -1830,7 +1830,7 @@ del_range_2 (ptrdiff_t from, ptrdiff_t from_byte,
at the end of the text before the gap. */
adjust_markers_for_delete (from, from_byte, to, to_byte);
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
/* Relocate point as if it were a marker. */
@ -1884,7 +1884,7 @@ modify_text (ptrdiff_t start, ptrdiff_t end)
BUF_COMPUTE_UNCHANGED (current_buffer, start - 1, end);
if (MODIFF <= SAVE_MODIFF)
record_first_change ();
MODIFF++;
modiff_incr (&MODIFF);
CHARS_MODIFF = MODIFF;
bset_point_before_scroll (current_buffer, Qnil);

2
src/keyboard.c
View file

@ -1238,7 +1238,7 @@ static void adjust_point_for_property (ptrdiff_t, bool);
Lisp_Object
command_loop_1 (void)
{
EMACS_INT prev_modiff = 0;
modiff_count prev_modiff = 0;
struct buffer *prev_buffer = NULL;
bool already_adjusted = 0;

22
src/lisp.h
View file

@ -3490,6 +3490,28 @@ integer_to_uintmax (Lisp_Object num, uintmax_t *n)
}
}
/* A modification count. These are wide enough, and incremented
rarely enough, so that they should never overflow a 60-bit counter
in practice, and the code below assumes this so a compiler can
generate better code if EMACS_INT is 64 bits. */
typedef intmax_t modiff_count;
INLINE modiff_count
modiff_incr (modiff_count *a)
{
modiff_count a0 = *a;
bool modiff_overflow = INT_ADD_WRAPV (a0, 1, a);
eassert (!modiff_overflow && *a >> 30 >> 30 == 0);
return a0;
}
INLINE Lisp_Object
modiff_to_integer (modiff_count a)
{
eassume (0 <= a && a >> 30 >> 30 == 0);
return make_int (a);
}
/* Defined in data.c. */
extern _Noreturn void wrong_choice (Lisp_Object, Lisp_Object);
extern void notify_variable_watchers (Lisp_Object, Lisp_Object,

2
src/marker.c
View file

@ -30,7 +30,7 @@ along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
static ptrdiff_t cached_charpos;
static ptrdiff_t cached_bytepos;
static struct buffer *cached_buffer;
static EMACS_INT cached_modiff;
static modiff_count cached_modiff;
/* Juanma Barranquero <lekktu@gmail.com> reported ~3x increased
bootstrap time when byte_char_debug_check is enabled; so this

2
src/pdumper.c
View file

@ -2797,7 +2797,7 @@ dump_hash_table (struct dump_context *ctx,
static dump_off
dump_buffer (struct dump_context *ctx, const struct buffer *in_buffer)
{
#if CHECK_STRUCTS && !defined (HASH_buffer_E8695CAE09)
#if CHECK_STRUCTS && !defined HASH_buffer_AE2C8CE357
# error "buffer changed. See CHECK_STRUCTS comment."
#endif
struct buffer munged_buffer = *in_buffer;

6
src/syntax.c
View file

@ -175,7 +175,7 @@ static ptrdiff_t find_start_value;
static ptrdiff_t find_start_value_byte;
static struct buffer *find_start_buffer;
static ptrdiff_t find_start_begv;
static EMACS_INT find_start_modiff;
static modiff_count find_start_modiff;
static Lisp_Object skip_chars (bool, Lisp_Object, Lisp_Object, bool);
@ -489,7 +489,7 @@ parse_sexp_propertize (ptrdiff_t charpos)
if (syntax_propertize__done <= charpos
&& syntax_propertize__done < zv)
{
EMACS_INT modiffs = CHARS_MODIFF;
modiff_count modiffs = CHARS_MODIFF;
safe_call1 (Qinternal__syntax_propertize,
make_fixnum (min (zv, 1 + charpos)));
if (modiffs != CHARS_MODIFF)
@ -608,7 +608,7 @@ find_defun_start (ptrdiff_t pos, ptrdiff_t pos_byte)
if (!NILP (Vcomment_use_syntax_ppss))
{
EMACS_INT modiffs = CHARS_MODIFF;
modiff_count modiffs = CHARS_MODIFF;
Lisp_Object ppss = call1 (Qsyntax_ppss, make_fixnum (pos));
if (modiffs != CHARS_MODIFF)
error ("syntax-ppss modified the buffer!");

2
src/textprop.c
View file

@ -89,7 +89,7 @@ modify_text_properties (Lisp_Object buffer, Lisp_Object start, Lisp_Object end)
BUF_COMPUTE_UNCHANGED (buf, b - 1, e);
if (MODIFF <= SAVE_MODIFF)
record_first_change ();
MODIFF++;
modiff_incr (&MODIFF);
bset_point_before_scroll (current_buffer, Qnil);

4
src/window.h
View file

@ -281,11 +281,11 @@ struct window
/* Displayed buffer's text modification events counter as of last time
display completed. */
EMACS_INT last_modified;
modiff_count last_modified;
/* Displayed buffer's overlays modification events counter as of last
complete update. */
EMACS_INT last_overlay_modified;
modiff_count last_overlay_modified;
/* Value of point at that time. Since this is a position in a buffer,
it should be positive. */