public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "kees at outflux dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109071] -Warray-bounds false positive warnings due to code duplication from jump threading
Date: Mon, 22 Apr 2024 20:15:59 +0000	[thread overview]
Message-ID: <bug-109071-4-cO70DI7xbq@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109071-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109071

--- Comment #8 from Kees Cook <kees at outflux dot net> ---
The warning is about:

      val = &sg->vals[index];


  poc.c:20:20: warning: array subscript 4 is above array bounds of 'int[4]'
[-Warray-bounds=]
   20 |     val = &sg->vals[index];
      |            ~~~~~~~~^~~~~~~


which happens before the warn(). And if the check is moved out of the
"assign()" function, the warning goes away:


    val = &sg->vals[index];

    if (index >= MAX_ENTRIES)
        warn();

    assign(0,    ptr, index);
    assign(*val, ptr, index);

Normally -Warray-bounds doesn't warn when a value is totally unknown (i.e.
"index" here can be [-INT_MAX,INT_MAX]). Why does the warning change when the
MAX_ENTRIES test is moved inside assign()?

  parent reply	other threads:[~2024-04-22 20:16 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-08 21:04 [Bug c/109071] New: -Warray-bounds warning when array index checked via inline kees at outflux dot net
2023-03-08 21:13 ` [Bug tree-optimization/109071] " pinskia at gcc dot gnu.org
2023-03-09 10:18 ` rguenth at gcc dot gnu.org
2023-03-09 16:15 ` kees at outflux dot net
2023-03-10 15:51 ` qinzhao at gcc dot gnu.org
2024-04-22 19:12 ` [Bug tree-optimization/109071] -Warray-bounds false positive warnings due to code duplication from jump threading qinzhao at gcc dot gnu.org
2024-04-22 19:21 ` kees at outflux dot net
2024-04-22 20:04 ` qinzhao at gcc dot gnu.org
2024-04-22 20:15 ` kees at outflux dot net [this message]
2024-04-22 21:19 ` qinzhao at gcc dot gnu.org
2024-05-13 14:21 ` qinzhao at gcc dot gnu.org
2024-05-14 16:19 ` qinzhao at gcc dot gnu.org

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bug-109071-4-cO70DI7xbq@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@gcc.gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).