diff mbox series

[committed] linemap_line_start: protect against location_t overflow (PR lto/88147)

Message ID 1549936961-49884-1-git-send-email-dmalcolm@redhat.com
State New
Headers show
Series [committed] linemap_line_start: protect against location_t overflow (PR lto/88147) | expand

Commit Message

David Malcolm Feb. 12, 2019, 2:02 a.m. UTC 
PR lto/88147 reports an assertion failure due to a bogus location_t value
when adding a line to a pre-existing line map, when there's a large
difference between the two line numbers.

For some "large differences", this leads to a location_t value that exceeds
LINE_MAP_MAX_LOCATION, in which case linemap_line_start returns 0.  This
isn't ideal, but at least should lead to safe degradation of location
information.

However, if the difference is very large, it's possible for the line
number offset (relative to the start of the map) to be sufficiently large
that overflow occurs when left-shifted by the column-bits, and hence
the check against the LINE_MAP_MAX_LOCATION limit fails, leading to
a seemingly-valid location_t value, but encoding the wrong location.  This
triggers the assertion failure:
  linemap_assert (SOURCE_LINE (map, r) == to_line);

The fix (thanks to Martin) is to check for overflow when determining
whether to reuse an existing map, and to not reuse it if it would occur.

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.

Committed to trunk as r268789.

gcc/ChangeLog: David Malcolm  <dmalcolm@redhat.com>
	PR lto/88147
	* input.c (selftest::test_line_offset_overflow): New selftest.
	(selftest::input_c_tests): Call it.

libcpp/ChangeLog: Martin Liska  <mliska@suse.cz>
	PR lto/88147
	* line-map.c (linemap_line_start): Don't reuse the existing line
	map if the line offset is sufficiently large to cause overflow
	when computing location_t values.
---
 gcc/input.c       | 30 ++++++++++++++++++++++++++++++
 libcpp/line-map.c |  4 ++++
 2 files changed, 34 insertions(+)
diff mbox series

Patch

diff --git a/gcc/input.c b/gcc/input.c
index bf1ca66..c589d70 100644
--- a/gcc/input.c
+++ b/gcc/input.c
@@ -3557,6 +3557,34 @@  for_each_line_table_case (void (*testcase) (const line_table_case &))
   ASSERT_EQ (num_cases_tested, 2 * 12);
 }
 
+/* Verify that when presented with a consecutive pair of locations with
+   a very large line offset, we don't attempt to consolidate them into
+   a single ordinary linemap where the line offsets within the line map
+   would lead to overflow (PR lto/88147).  */
+
+static void
+test_line_offset_overflow ()
+{
+  line_table_test ltt (line_table_case (5, 0));
+
+  linemap_add (line_table, LC_ENTER, false, "foo.c", 0);
+  linemap_line_start (line_table, 1, 100);
+  location_t loc_a = linemap_line_start (line_table, 2578, 255);
+  assert_loceq ("foo.c", 2578, 0, loc_a);
+
+  const line_map_ordinary *ordmap_a = LINEMAPS_LAST_ORDINARY_MAP (line_table);
+  ASSERT_EQ (ordmap_a->m_column_and_range_bits, 13);
+  ASSERT_EQ (ordmap_a->m_range_bits, 5);
+
+  location_t loc_b = linemap_line_start (line_table, 404198, 512);
+  assert_loceq ("foo.c", 404198, 0, loc_b);
+
+  /* We should have started a new linemap, rather than attempting to store
+     a very large line offset.  */
+  const line_map_ordinary *ordmap_b = LINEMAPS_LAST_ORDINARY_MAP (line_table);
+  ASSERT_NE (ordmap_a, ordmap_b);
+}
+
 /* Run all of the selftests within this file.  */
 
 void
@@ -3596,6 +3624,8 @@  input_c_tests ()
   for_each_line_table_case (test_lexer_char_constants);
 
   test_reading_source_line ();
+
+  test_line_offset_overflow ();
 }
 
 } // namespace selftest
diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index ff679ed..0e30b4b 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -742,6 +742,10 @@  linemap_line_start (struct line_maps *set, linenum_type to_line,
       if (line_delta < 0
 	  || last_line != ORDINARY_MAP_STARTING_LINE_NUMBER (map)
 	  || SOURCE_COLUMN (map, highest) >= (1U << (column_bits - range_bits))
+	  || ( /* We can't reuse the map if the line offset is sufficiently
+		  large to cause overflow when computing location_t values.  */
+	      (to_line - ORDINARY_MAP_STARTING_LINE_NUMBER (map))
+	      >= (1U << (CHAR_BIT * sizeof (linenum_type) - column_bits)))
 	  || range_bits < map->m_range_bits)
 	map = linemap_check_ordinary
 	        (const_cast <line_map *>