Here, in dwarfread.c:process_full_comp_unit:
/* Set symtab language to language from DW_AT_language. If the
compilation is from a C file generated by language preprocessors, do
not set the language if it was already deduced by start_subfile. */
if (!(cu->language == language_c
&& COMPUNIT_FILETABS (cust)->language != language_c))
COMPUNIT_FILETABS (cust)->language = cu->language;
in case start_subfile doesn't manage to deduce a language
COMPUNIT_FILETABS(cust)->language ends up as language_unknown, not
language_c. So the condition above evals false and we never set the
language from the cu's language.
gdb/ChangeLog:
2015-08-20 Pedro Alves <palves@redhat.com>
* dwarf2read.c (process_full_comp_unit): To tell whether
start_subfile managed to deduce a language, test for
language_unknown instead of language_c.
gdb/testsuite/ChangeLog:
2015-08-20 Pedro Alves <palves@redhat.com>
* gdb.dwarf2/comp-unit-lang.exp: New file.
* gdb.dwarf2/comp-unit-lang.c: New file.
