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From: "mark at klomp dot org" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug general/29141] _FORTIFY_SOURCE=3 fail for gcc 12/glibc 2.35
Date: Wed, 11 May 2022 11:10:03 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29141

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mark at klomp dot org,
                   |                            |siddhesh at sourceware dot=
 org

--- Comment #1 from Mark Wielaard <mark at klomp dot org> ---
This is interesting. I recently fixed a similar warning in gdb (also for
-Werror=3Dstringop-overflow, but not _FORTIFY_SOURCE related):
https://sourceware.org/pipermail/gdb-patches/2022-May/188694.html

I have added Siddhesh to the CC who might have seen this earlier.
Background is that in elfutils we are trying to use _FORTIFY_SOURCE=3D3 whe=
n it
is available using this configure snippet:

# See if we can add -D_FORTIFY_SOURCE=3D2 or =3D3. Don't do it if it is alr=
eady
# (differently) defined or if it generates warnings/errors because we
# don't use the right optimisation level (string.h will warn about that).
AC_MSG_CHECKING([whether to add -D_FORTIFY_SOURCE=3D2 or =3D3 to CFLAGS])
case "$CFLAGS" in
  *-D_FORTIFY_SOURCE=3D*)
    AC_MSG_RESULT([no, already there])
    ;;
  *)
    save_CFLAGS=3D"$CFLAGS"
    # Try 3 first.
    CFLAGS=3D"-D_FORTIFY_SOURCE=3D3 $save_CFLAGS -Werror"
    fortified_cflags=3D""
    AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
      #include <string.h>
      int main() { return 0; }
    ]])], [ AC_MSG_RESULT([yes -D_FORTIFY_SOURCE=3D3])
            fortified_cflags=3D"-D_FORTIFY_SOURCE=3D3" ], [])

    # If that didn't work, try 2.
    if test -z "$fortified_cflags"; then
      CFLAGS=3D"-D_FORTIFY_SOURCE=3D2 $save_CFLAGS -Werror"
      AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
        #include <string.h>
        int main() { return 0; }
      ]])], [ AC_MSG_RESULT([yes -D_FORTIFY_SOURCE=3D2])
              fortified_cflags=3D"-D_FORTIFY_SOURCE=3D2" ],
              [ AC_MSG_RESULT([no, cannot be used])])
    fi
    CFLAGS=3D"$fortified_cflags $save_CFLAGS"
    CXXFLAGS=3D"$fortified_cflags $CXXFLAGS"
    ;;
esac


But it seems to produce gcc warnings like the above, so either our configure
foo is bad or we simply have to always use _FORTIFY_SOURCE=3D2.

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