https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88147
--- Comment #21 from David Malcolm <dmalcolm at gcc dot gnu.org> --- Author: dmalcolm Date: Tue Feb 12 01:09:31 2019 New Revision: 268789 URL: https://gcc.gnu.org/viewcvs?rev=268789&root=gcc&view=rev Log: linemap_line_start: protect against location_t overflow (PR lto/88147) 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. gcc/ChangeLog: David Malcolm <dmalc...@redhat.com> PR lto/88147 * input.c (selftest::test_line_offset_overflow): New selftest. (selftest::input_c_tests): Call it. libcpp/ChangeLog: Martin Liska <mli...@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. Modified: trunk/gcc/ChangeLog trunk/gcc/input.c trunk/libcpp/ChangeLog trunk/libcpp/line-map.c
