[Bug analyzer/106626] Improvements to wording of -Wanalyzer-out-of-bounds

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106626

--- Comment #3 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:7c655699ed51b0c987e5472767db48b19044ae05

commit r13-4427-g7c655699ed51b0c987e5472767db48b19044ae05
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Wed Nov 30 21:26:42 2022 -0500

    analyzer: add note about valid subscripts [PR106626]

    Consider -fanalyzer on:

    #include <stdint.h>

    int32_t arr[10];

    void int_arr_write_element_after_end_off_by_one(int32_t x)
    {
      arr[10] = x;
    }

    Trunk x86_64: https://godbolt.org/z/17zn3qYY4

    Currently we emit:

    <source>: In function 'int_arr_write_element_after_end_off_by_one':
    <source>:7:11: warning: buffer overflow [CWE-787]
[-Wanalyzer-out-of-bounds]
        7 |   arr[10] = x;
          |   ~~~~~~~~^~~
      event 1
        |
        |    3 | int32_t arr[10];
        |      |         ^~~
        |      |         |
        |      |         (1) capacity is 40 bytes
        |
        +--> 'int_arr_write_element_after_end_off_by_one': events 2-3
               |
               |    5 | void int_arr_write_element_after_end_off_by_one(int32_t
x)
               |      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
               |      |      |
               |      |      (2) entry to
'int_arr_write_element_after_end_off_by_one'
               |    6 | {
               |    7 |   arr[10] = x;
               |      |   ~~~~~~~~~~~
               |      |           |
               |      |           (3) out-of-bounds write from byte 40 till
byte 43 but 'arr' ends at byte 40
               |
    <source>:7:11: note: write of 4 bytes to beyond the end of 'arr'
        7 |   arr[10] = x;
          |   ~~~~~~~~^~~

    This is worded in terms of bytes, due to the way -Wanalyzer-out-of-bounds
    is implemented, but this isn't what the user wrote.

    This patch tries to get closer to the user's code by adding a note about
    array bounds when we're referring to an array.  In the above example it
    adds this trailing note:

      note: valid subscripts for 'arr' are '[0]' to '[9]'

    gcc/analyzer/ChangeLog:
            PR analyzer/106626
            * bounds-checking.cc (out_of_bounds::maybe_describe_array_bounds):
            New.
            (buffer_overflow::emit): Call maybe_describe_array_bounds.
            (buffer_overread::emit): Likewise.
            (buffer_underflow::emit): Likewise.
            (buffer_underread::emit): Likewise.

    gcc/testsuite/ChangeLog:
            PR analyzer/106626
            * gcc.dg/analyzer/call-summaries-2.c: Add dg-message for expected
            note about valid indexes.
            * gcc.dg/analyzer/out-of-bounds-1.c: Likewise, fixing up existing
            dg-message directives.
            * gcc.dg/analyzer/out-of-bounds-write-char-arr.c: Likewise.
            * gcc.dg/analyzer/out-of-bounds-write-int-arr.c: Likewise.

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