[Bug analyzer/108689] New: RFE: more precise handling of "fread"-style functions in -fanalyzer

[Bug analyzer/108689] New: RFE: more precise handling of "fread"-style functions in -fanalyzer

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108689

            Bug ID: 108689
           Summary: RFE: more precise handling of "fread"-style functions
                    in -fanalyzer
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

We currently handle calls to "fread" (in sm-file.cc's class kf_fread) by
assuming that any call to fread fully clobbers the memory region pointed to.

This misses cases where e.g. the code doesn't check that the read succeeded, or
that the sizes are wrong.

We should probably bifurcate the analysis to cover:
- errors
- full read
- partial read

or somesuch.

(and do the same for "read").

[Bug analyzer/108689] RFE: more precise handling of "fread"-style functions in -fanalyzer

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108689

--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:c300e251f5b22d15b126f3c643cd55a119994e48

commit r13-5733-gc300e251f5b22d15b126f3c643cd55a119994e48
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Tue Feb 7 16:10:20 2023 -0500

    analyzer: fix -Wanalyzer-use-of-uninitialized-value false +ve on "read"
[PR108661]

    My integration testing shows many false positives from
    -Wanalyzer-use-of-uninitialized-value.

    One cause turns out to be that as of r13-1404-g97baacba963c06
    fd_state_machine::on_stmt recognizes calls to "read", and returns true,
    so that region_model::on_call_post doesn't call handle_unrecognized_call
    on them, and so the analyzer erroneously "thinks" that the buffer
    pointed to by "read" is never touched by the "read" call.

    This works for "fread" because sm-file.cc implements kf_fread, which
    handles calls to "fread" by clobbering the buffer pointed to.  In the
    long term we should probably be smarter about this and bifurcate the
    analysis to consider e.g. errors vs full reads vs partial reads, etc
    (which I'm tracking in PR analyzer/108689).

    In the meantime, this patch adds a kf_read for "read" analogous to the
    one for "fread", fixing 6 false positives seen in git-2.39.0 and
    2 in haproxy-2.7.1.

    gcc/analyzer/ChangeLog:
            PR analyzer/108661
            * sm-fd.cc (class kf_read): New.
            (register_known_fd_functions): Register "read".
            * sm-file.cc (class kf_fread): Update comment.

    gcc/testsuite/ChangeLog:
            PR analyzer/108661
            * gcc.dg/analyzer/fread-pr108661.c: New test.
            * gcc.dg/analyzer/read-pr108661.c: New test.

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