analyzer: new warning: -Wanalyzer-unterminated-string [PR105899]

This patch adds new functions to the analyzer for checking that
an argument at a callsite is a pointer to a valid null-terminated
string, and uses this for the following known functions:

- error (param 3, the format string)
- error_at_line (param 5, the format string)
- putenv
- strchr (1st param)
- strcpy (2nd param)
- strdup

Currently the check merely detects pointers to unterminated string
constants, and adds a new -Wanalyzer-unterminated-string to complain
about that.  I'm experimenting with detecting other ways in which
a buffer can fail to be null-terminated, and for other problems with
such buffers, but this patch at least adds the framework for wiring
up the check to specific parameters of known_functions.

gcc/analyzer/ChangeLog:
	PR analyzer/105899
	* analyzer.opt (Wanalyzer-unterminated-string): New.
	* call-details.cc
	(call_details::check_for_null_terminated_string_arg): New.
	* call-details.h
	(call_details::check_for_null_terminated_string_arg): New decl.
	* kf-analyzer.cc (class kf_analyzer_get_strlen): New.
	(register_known_analyzer_functions): Register it.
	* kf.cc (kf_error::impl_call_pre): Check that format arg is a
	valid null-terminated string.
	(kf_putenv::impl_call_pre): Likewise for the sole param.
	(kf_strchr::impl_call_pre): Likewise for the first param.
	(kf_strcpy::impl_call_pre): Likewise for the second param.
	(kf_strdup::impl_call_pre): Likewise for the sole param.
	* region-model.cc (get_strlen): New.
	(struct call_arg_details): New.
	(inform_about_expected_null_terminated_string_arg): New.
	(class unterminated_string_arg): New.
	(region_model::check_for_null_terminated_string_arg): New.
	* region-model.h
	(region_model::check_for_null_terminated_string_arg): New decl.

gcc/ChangeLog:
	PR analyzer/105899
	* doc/analyzer.texi (__analyzer_get_strlen): New.
	* doc/invoke.texi: Add -Wanalyzer-unterminated-string.

gcc/testsuite/ChangeLog:
	PR analyzer/105899
	* gcc.dg/analyzer/analyzer-decls.h (__analyzer_get_strlen): New.
	* gcc.dg/analyzer/error-1.c (test_error_unterminated): New.
	(test_error_at_line_unterminated): New.
	* gcc.dg/analyzer/null-terminated-strings-1.c: New test.
	* gcc.dg/analyzer/putenv-1.c (test_unterminated): New.
	* gcc.dg/analyzer/strchr-1.c (test_unterminated): New.
	* gcc.dg/analyzer/strcpy-1.c (test_unterminated): New.
	* gcc.dg/analyzer/strdup-1.c (test_unterminated): New.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>