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>

0 files changed, 0 insertions, 0 deletions