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From: "dcb314 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/103939] New: memset with sizeof in wrong place not detected ?
Date: Fri, 07 Jan 2022 11:21:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103939

            Bug ID: 103939
           Summary: memset with sizeof in wrong place not detected ?
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
  Target Milestone: ---

For this C++ code:

$ more jan7d.cc

#include <cstring>

struct S
{
        int a;
        int b;
        int c;
        int d;
};

void f( S * ps)
{
   memset(ps, sizeof(S), 0xff);
}

compiled with recent gcc trunk:

$ /home/dcb/gcc/results/bin/gcc -c -g -O2 -Wall -Wextra -pedantic jan7d.cc
$=20

compiled by clang-13:

$ /usr/bin/clang++ -c -g -O2 -Wall -Wextra -pedantic jan7d.cc
jan7d.cc:14:15: warning: setting buffer to a 'sizeof' expression; did you m=
ean
to transpose the last two arguments? [-Wmemset-transposed-args]
   memset(ps, sizeof(S), 0xff);
              ^
jan7d.cc:14:15: note: cast the second argument to 'int' to silence
1 warning generated.=