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Fix linemap corruption after very wide source lines (PR c++/72803)

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PR c++/72803 describes an issue where a fix-it hint is to be emitted at
column 512 of a 511-column source line, leading to an ICE.

The root cause is a bug in linemap_line_start, when transitioning from
lines >= 512 in width to narrow lines.

The wide line in the reproducer has a line map with:
  m_column_and_range_bits = 15, m_range_bits = 5
giving 10 effective bits for representing columns, so that columns <= 1023
can be represented.

When parsing the following line,
  linemap_line_start (..., ..., max_column_hint=0);
is called.  This leads to the "add_map" logic, due to this condition:
      || (max_column_hint <= 80 && effective_column_bits >= 10)
i.e. the new line is sufficiently narrower than the old one to
potentially use a new linemap (so as to conserve values within the
location_t space).

It then attempts to avoid allocating a new line map.  Part of the logic
to determine if we really need a new line map is this condition:
   SOURCE_COLUMN (map, highest) >= (1U << column_bits)
The above condition is incorrect: we need to determine if the highest
column we've handed out will fit within the proposed *effective* column
bits, but "column_bits" here is the column plus the range bits, rather
than just the column bits.

Hence in this case linemap_line_start erroneously decides that we don't
need a new line map, and updates the column bits within the existing
line map, so any location_t values we've already handed out within it
that are offset from the start by
  >= (1<<new_column_and_range_bits)
effectively change meaning, leading to incorrect line&column information
when decoding them, and various "interesting" ways for the linemap
code to fail.

The fix is to use the effective column bits in the above conditional.

gcc/ChangeLog:
	PR c++/72803
	* input.c (selftest::test_accessing_ordinary_linemaps): Verify
	that the transition from a max line width >= 1<<10 to narrower
	lines works correctly.

gcc/testsuite/ChangeLog:
	PR c++/72803
	* g++.dg/diagnostic/pr72803.C: New test case.

libcpp/ChangeLog:
	PR c++/72803
	* line-map.c (linemap_line_start): When determining if the highest
	column given out so far will fit into a proposed change to the
	current map, use the effective number of column bits, rather than
	the total number of column + range bits.

From-SVN: r244199
This commit is contained in:
David Malcolm 2017-01-07 21:33:59 +00:00 • committed by David Malcolm
parent ff98fa955b
commit 5ccf1d8d10
6 changed files with 42 additions and 1 deletions
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7
gcc/ChangeLog
View file

@ -1,3 +1,10 @@
2017-01-07 David Malcolm <dmalcolm@redhat.com>
PR c++/72803
* input.c (selftest::test_accessing_ordinary_linemaps): Verify
that the transition from a max line width >= 1<<10 to narrower
lines works correctly.
2017-01-07 Alexandre Oliva <aoliva@redhat.com>
* doc/options.texi (PerFunction): New.

12
gcc/input.c
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@ -1688,6 +1688,17 @@ test_accessing_ordinary_linemaps (const line_table_case &case_)
linemap_line_start (line_table, 3, 2000);
location_t loc_e = linemap_position_for_column (line_table, 700);
/* Transitioning back to a short line. */
linemap_line_start (line_table, 4, 0);
location_t loc_back_to_short = linemap_position_for_column (line_table, 100);
if (should_have_column_data_p (loc_back_to_short))
{
/* Verify that we switched to short lines in the linemap. */
line_map_ordinary *map = LINEMAPS_LAST_ORDINARY_MAP (line_table);
ASSERT_EQ (7, map->m_column_and_range_bits - map->m_range_bits);
}
linemap_add (line_table, LC_LEAVE, false, NULL, 0);
/* Multiple files. */
@ -1702,6 +1713,7 @@ test_accessing_ordinary_linemaps (const line_table_case &case_)
assert_loceq ("foo.c", 2, 1, loc_c);
assert_loceq ("foo.c", 2, 17, loc_d);
assert_loceq ("foo.c", 3, 700, loc_e);
assert_loceq ("foo.c", 4, 100, loc_back_to_short);
assert_loceq ("bar.c", 1, 150, loc_f);
ASSERT_FALSE (is_location_from_builtin_token (loc_a));

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2017-01-07 David Malcolm <dmalcolm@redhat.com>
PR c++/72803
* g++.dg/diagnostic/pr72803.C: New test case.
2017-01-07 Martin Sebor <msebor@redhat.com>
* gcc.dg/attr-alloc_size-3.c: Remove regex made redundant by r243461.

9
gcc/testsuite/g++.dg/diagnostic/pr72803.C Normal file
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@ -0,0 +1,9 @@
/* Long line, with a close brace at column 511, hence with the insertion
point for the missing semicolon at column 512. */
class test { }
# 1 "" 1
// The line directive appears to be necessary to trigger the ICE
// { dg-error "style of line directive is a GCC extension" "" { target *-*-* } .-2 }
/* Verify that we get the correct line and column for the diagnostic. */
// { dg-error "512: expected .;. after class definition" "" { target *-*-* } 3 }

8
libcpp/ChangeLog
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@ -1,3 +1,11 @@
2017-01-07 David Malcolm <dmalcolm@redhat.com>
PR c++/72803
* line-map.c (linemap_line_start): When determining if the highest
column given out so far will fit into a proposed change to the
current map, use the effective number of column bits, rather than
the total number of column + range bits.
2017-01-01 Jakub Jelinek <jakub@redhat.com>
Update copyright years.

2
libcpp/line-map.c
View file

@ -752,7 +752,7 @@ linemap_line_start (struct line_maps *set, linenum_type to_line,
single line we can sometimes just increase its column_bits instead. */
if (line_delta < 0
|| last_line != ORDINARY_MAP_STARTING_LINE_NUMBER (map)
|| SOURCE_COLUMN (map, highest) >= (1U << column_bits)
|| SOURCE_COLUMN (map, highest) >= (1U << (column_bits - range_bits))
|| range_bits < map->m_range_bits)
map = linemap_check_ordinary
(const_cast <line_map *>