analyzer: fix leak false positives on "*UNKNOWN = PTR;" [PR108252]

analyzer: fix leak false positives on "*UNKNOWN = PTR;" [PR108252]

PR analyzer/108252 reports a false positive from -Wanalyzer-malloc-leak on
code like this:

  *ptr_ptr = strdup(EXPR);

where ptr_ptr is an UNKNOWN_VALUE.

When we handle:
  *UNKNOWN = PTR;
store::set_value normally marks *PTR as having escaped, and this means
we don't report PTR as leaking when the last usage of PTR is lost.

However this only works for cases where PTR is a region_svalue.
In the example in the bug, it's a conjured_svalue, rather than a
region_svalue.  A similar problem can arise for FDs, which aren't
pointers.

This patch fixes the bug by updating store::set_value to mark any
values stored via *UNKNOWN = VAL as not leaking.

Additionally, sm-malloc.cc's known_allocator_p hardcodes strdup and
strndup as allocators (and thus transitioning their result to
"unchecked"), but we don't implement known_functions for these, leading
to the LHS being a CONJURED_SVALUE, rather than a region_svalue to a
heap-allocated region.  A similar issue happens with functions marked
with __attribute__((malloc)).  As part of a "belt and braces" fix, the
patch also updates the handling of these functions, so that they use
heap-allocated regions.

gcc/analyzer/ChangeLog:
	PR analyzer/108252
	* kf.cc (class kf_strdup): New.
	(class kf_strndup): New.
	(register_known_functions): Register them.
	* region-model.cc (region_model::on_call_pre): Use
	&HEAP_ALLOCATED_REGION for the default result of an external
	function with the "malloc" attribute, rather than CONJURED_SVALUE.
	(region_model::get_or_create_region_for_heap_alloc): Allow
	"size_in_bytes" to be NULL.
	* store.cc (store::set_value): When handling *UNKNOWN = VAL,
	mark VAL as "maybe bound".

gcc/testsuite/ChangeLog:
	PR analyzer/108252
	* gcc.dg/analyzer/attr-malloc-pr108252.c: New test.
	* gcc.dg/analyzer/fd-leak-pr108252.c: New test.
	* gcc.dg/analyzer/flex-with-call-summaries.c: Remove xfail from
	warning false +ve directives.
	* gcc.dg/analyzer/pr103217-2.c: Add -Wno-analyzer-too-complex.
	* gcc.dg/analyzer/pr103217-3.c: Likewise.
	* gcc.dg/analyzer/strdup-pr108252.c: New test.
	* gcc.dg/analyzer/strndup-pr108252.c: New test.

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