[Bug c++/106738] New: -Wlarger-than triggering for *.LASAN0 section

[Bug c++/106738] New: -Wlarger-than triggering for *.LASAN0 section

[frolov.da at phystech dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106738

            Bug ID: 106738
           Summary: -Wlarger-than triggering for *.LASAN0 section
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: frolov.da at phystech dot edu
  Target Milestone: ---

The behaviour of the warning flag -Wlarger-than is described in documentationL

> warn whenever an object is defined whose size exceeds byte-size. 
> -Wlarger-than=‘PTRDIFF_MAX’ is enabled by default. Warnings controlled by the
> option can be disabled either by specifying byte-size of ‘SIZE_MAX’ or more or 
> by -Wno-larger-than.
> Also warn for calls to bounded functions such as memchr or strnlen that
> specify a bound greater than the largest possible object, which is
> ‘PTRDIFF_MAX’ bytes by default.

I've tried to build the next example:

#include <assert.h>
void foo () {
    assert (false);
}

$ g++ -O2 -c -Wlarger-than=16 -fsanitize=address minimal.cpp

And got a warning:
cc1plus: warning: size of ‘*.LASAN0’ 192 bytes exceeds maximum object size 16
[-Wlarger-than=]

It looks like a false triggering. From my point of view the user should not
monitor the size of the analyzer section.

Moreover, if we would try to add another assert:

#include <assert.h>
void foo () {
    assert (false);
}
void goo () {
    assert (false);
}

Then we'll get:
cc1plus: warning: size of ‘*.LASAN0’ 256 bytes exceeds maximum object size 16
[-Wlarger-than=]

[Bug c++/106738] -Wlarger-than triggering for *.LASAN0 section

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106738

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
           Keywords|                            |diagnostic
   Last reconfirmed|                            |2022-08-25

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug middle-end/106738] -Wlarger-than triggering for *.LASAN0 section

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106738

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Maybe DECL_IGNORED_P or DECL_ARTIFICIAL should be checked before calling
warning in stor-layout.cc?

Because:
in asan.cc:
      ASM_GENERATE_INTERNAL_LABEL (buf, "LASAN", 0);
      var = build_decl (UNKNOWN_LOCATION, VAR_DECL, get_identifier (buf),
                        type);
      TREE_STATIC (var) = 1;
      TREE_PUBLIC (var) = 0;
      DECL_ARTIFICIAL (var) = 1;
      DECL_IGNORED_P (var) = 1;

...
in stor-layout.cc before doing the warning call:
  /* If requested, warn about definitions of large data objects.  */
  if ((code == PARM_DECL || (code == VAR_DECL && !DECL_NONLOCAL_FRAME (decl)))
      && !DECL_EXTERNAL (decl))