[Bug c++/61294] New: [4.9 Regression] erroneous memset used with constant zero length parameter warning

[Bug c++/61294] New: [4.9 Regression] erroneous memset used with constant zero length parameter warning

[orion at cora dot nwra.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

            Bug ID: 61294
           Summary: [4.9 Regression] erroneous memset used with constant
                    zero length parameter warning
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: orion at cora dot nwra.com

Created attachment 32846
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=32846&action=edit
preprocessed test case

$ g++ -std=c++11 -O2 -c test.cxx
In function 'void* memset(void*, int, size_t)',
    inlined from 'static void
vtkDistributedDataFilter::AddConstantUnsignedCharPointArray(vtkUnstructuredGrid*,
const char*, unsigned char)' at test.cxx:31883:29:
test.cxx:15303:32: warning: call to '__warn_memset_zero_len' declared with
attribute warning: memset used with constant zero length parameter; this could
be due to transposed parameters
       __warn_memset_zero_len ();
                                ^

# g++ -v
Using built-in specs.
COLLECT_GCC=/usr/bin/g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.9.0/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --enable-multilib --with-system-zlib
--enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --disable-libgcj
--with-isl=/builddir/build/BUILD/gcc-4.9.0-20140518/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.9.0-20140518/obj-x86_64-redhat-linux/cloog-install
--enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.9.0 20140518 (Red Hat 4.9.0-5) (GCC)

No warning with 4.8.2 (or without -O2)

[Bug c++/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Happens on an isolated path where GCC optimized

 if (len)
   ....

 memset (p, val, len);

to

 if (len == 0)
   {
  ....
   memset (p, val, 0);
   }
 else
   {
 .....
   memset (p, val, len);
   }

can happen and there is no good way around that, thus it's a false positive.

It's the

   if (grid->Points)

check that is false when the compiler can compute the 'len' parameter will
be zero.  Maybe that helps you deciding whether it really is a false positive
or not (well, yes, whether you are calling memset with len == 0, which
might be valid, but we warn about it).

[Bug c++/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2014-05-26
     Ever confirmed|0                           |1

[Bug c++/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.9.1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
That is,

inline vtkIdType vtkPointSet::GetNumberOfPoints()
{
  if (this->Points)
    {
    return this->Points->GetNumberOfPoints();
    }
  else
    {
    return 0;
    }
}

and


void vtkDistributedDataFilter::AddConstantUnsignedCharPointArray(
  vtkUnstructuredGrid *grid, const char *arrayName, unsigned char val)
{
  vtkIdType npoints = grid->GetNumberOfPoints();
  unsigned char *vals = new unsigned char [npoints];
  memset(vals, val, npoints);
}

may allocate zero points and initialize zero points due to that extra
"safety" check.  If you put a assert (npoints > 0) in there then
the warning will go away.

[Bug c++/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[orion at cora dot nwra.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

--- Comment #3 from Orion Poplawski <orion at cora dot nwra.com> ---
Hmm, now all of a sudden I don't seem to be able to reproduce this.  Thanks for
your comments though.  I play around if it re-appears.  The problem was
compounded by the use of -Wl,--fatal-warnings so it was preventing linkage.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
                 CC|                            |jason at gcc dot gnu.org
          Component|c++                         |middle-end

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
It's clearly a false positive; the warning is intended to catch calls where the
user wrote a 0 directly in the argument list for memset (which suggests
accidentally transposed arguments), not cases where some execution path might
result in a 0 argument (which works fine).  The only question is what there is
to fix either in GCC or GLIBC to avoid this false positive.

A simple way to work around this is to guard the memset with if (npoints > 0).

The false positive seems to come up fairly often:

https://sourceware.org/ml/binutils/2012-02/msg00073.html
https://bugzilla.redhat.com/show_bug.cgi?id=452219
https://www.nsnam.org/bugzilla/show_bug.cgi?id=1165

Changing component to middle-end.

Reduced C testcase:

typedef __SIZE_TYPE__ size_t;
extern void *malloc (size_t __size) __attribute__ ((__malloc__)) __attribute__
((__warn_unused_result__));
extern void *memset (void *__s, int __c, size_t __n) __attribute__
((__nonnull__ (1)));
extern void __warn_memset_zero_len (void) __attribute__((__warning__ ("memset
used with constant zero length parameter; this could be due to transposed
parameters")));
extern __inline __attribute__((__always_inline__))
__attribute__((__artificial__))
void *
  memset (void *__dest, int __ch, size_t __len)
{
  if (__builtin_constant_p (__len) && __len == 0
      && (!__builtin_constant_p (__ch) || __ch != 0))
    {
      __warn_memset_zero_len ();
      return __dest;
    }
  return __builtin___memset_chk (__dest, __ch, __len,
                 __builtin_object_size (__dest, 0));
}

int i;
inline int f()
{
  if (i)
    return i;
  else
    return 0;
}

void g(unsigned char val)
{
  int len = f();
  void *p = malloc (len);
  memset (p, val, len);
}

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I wonder if we just shouldn't move this warning to GCC and in glibc remove it
if sufficiently new GCC version is used.
GCC could then warn about this in the FEs, only in the cases where user likely
made a mistake (i.e. when third argument is literal 0 (rather than e.g. an
expression folded to 0) and second argument is not literal 0.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Mon Jul 14 07:36:39 2014
New Revision: 212510

URL: https://gcc.gnu.org/viewcvs?rev=212510&root=gcc&view=rev
Log:
    PR middle-end/61294
gcc/c-family/
    * c.opt (Wmemset-transposed-args): New warning.
gcc/c/
    * c-parser.c (c_parser_expr_list): Add new argument literal_zero_mask.
    If non-NULL, call c_parser_check_literal_zero.
    (c_parser_check_literal_zero): New function.
    (c_parser_postfix_expression_after_primary): Adjust
    c_parser_expr_list caller, handle -Wmemset-transposed-args.
gcc/cp/
    * cp-tree.h (LITERAL_ZERO_P): Define.
    * parser.c (cp_parser_parenthesized_expression_list): Add
    want_literal_zero_p argument, if true, for literal zeros
    insert INTEGER_CSTs with LITERAL_ZERO_P flag set.
    (cp_parser_postfix_expression): Adjust
    cp_parser_parenthesized_expression_list caller, handle
    -Wmemset-transposed-args.
    (literal_zeros): New variable.
gcc/
    * doc/invoke.texi (-Wmemset-transposed-args): Document.
gcc/testsuite/
    * c-c++-common/Wmemset-transposed-args1.c: New test.
    * c-c++-common/Wmemset-transposed-args2.c: New test.
    * g++.dg/warn/Wmemset-transposed-args-1.C: New test.

Added:
    trunk/gcc/testsuite/c-c++-common/Wmemset-transposed-args1.c
    trunk/gcc/testsuite/c-c++-common/Wmemset-transposed-args2.c
    trunk/gcc/testsuite/g++.dg/warn/Wmemset-transposed-args-1.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c.opt
    trunk/gcc/c/ChangeLog
    trunk/gcc/c/c-parser.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/parser.c
    trunk/gcc/doc/invoke.texi
    trunk/gcc/testsuite/ChangeLog

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.1                       |4.9.2

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.1 has been released.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amodra at gmail dot com

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 62033 has been marked as a duplicate of this bug. ***

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.2                       |4.9.3

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.2 has been released.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
           Priority|P3                          |P2
      Known to work|                            |5.0

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
doesn't exactly work with GCC 5 now but requires an updated GLIBC AFAICS.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |carlos at redhat dot com

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Carlos/Siddhesh, can you please adjust the glibc headers, so that for
__GNUC_PREREQ (5, 0) it doesn't contain the __warn_memset_zero_len stuff, as
GCC will handle warning about it?

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[carlos at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

carlos at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |carlos at gcc dot gnu.org

--- Comment #12 from carlos at gcc dot gnu.org ---
(In reply to Jakub Jelinek from comment #11)
> Carlos/Siddhesh, can you please adjust the glibc headers, so that for
> __GNUC_PREREQ (5, 0) it doesn't contain the __warn_memset_zero_len stuff, as
> GCC will handle warning about it?

Siddhesh will have a look at fixing this in master.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[siddhesh at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

--- Comment #13 from Siddhesh Poyarekar <siddhesh at redhat dot com> ---
Fixed in glibc:

commit 1721f0a406e52f976f9daf6f59acf42c1dbd33ff
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Nov 27 11:15:45 2014 +0530

    Don't use __warn_memset_zero_len for gcc-5.0 or newer

    gcc now warns when the arguments to memset may have been accidentally
    transposed (i.e. length set to zero instead of the byte), so we don't
    need that bit of the code in glibc headers anymore.

    Tested on x86_64.  Coe generated by gcc 4.8 is identical with or
    without the patch.  I also tested gcc master, which does not result in
    any new failures.  It does fail quite a few FORTIFY_SOURCE tests, but
    those failures are not due to this patch.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.3 has been released.

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.3                       |4.9.4

[Bug middle-end/61294] [4.9 Regression] erroneous memset used with constant zero length parameter warning

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61294

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |martin at v dot loewis.de

--- Comment #16 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 16794 has been marked as a duplicate of this bug. ***