Bug#1055750: gfortran: [armhf] Yield SIGBUS when compiling with -fstack-clash-protection

[Rafael Laboissière <rafael@debian.org>]

The attached file bug-1055750.tgz contains a minimal code that 
triggers the bug on an armhf system : 
 
    $ ./run 
    ***** Compile without -fstack-clash-protection & run 
    /usr/bin/ld: warning: /tmp/cc9l2GJa.o: requires executable stack (because the .note.GNU-stack section is executable) 
    ***** Compile with -fstack-clash-protection & run 
    /usr/bin/ld: warning: /tmp/ccP0miz5.o: requires executable stack (because the .note.GNU-stack section is executable)

    Program received signal SIGBUS: Access to an undefined portion of a memory object.

    Backtrace for this error:
    Bus error

* Rafael Laboissière <rafael@debian.org> [2023-11-10 15:52]:

> Package: gfortran
> Version: 13.2.0-1
> Severity: normal
>
> Dear Maintainer,
>
> The motivation for the present bug report comes from Bug#1055228. Since 
> version 1.22.1 of dpkg-dev was released (on October 30), the plplot 
> package FTBFS due to a failing compilation of one of Fortran examples, 
> which is exercised as a unit test during package building.
>
> The package built fine previously. The problem is triggered by the change 
> in dpkg-buildflags, which now includes -fstack-clash-protection in 
> FFLAGS.
>
> I am attaching to this bug message a shell script that can reliably 
> trigger the bug on an armhf system. Here is the output:
>
>    $ ./gfortran-stack-clash-protection-armhf-bug.sh
>    […]
>    Program received signal SIGBUS: Access to an undefined portion of a memory object.
>
>    Backtrace for this error:
>    Bus error
>
> Note that the bug does not happen on amd64. Also, it does not happen on 
> armhf when the option -fstack-clash-protection is not used in the 
> invocation of gfortran.
>
> As far as I can tell, the problem is due to a global variable (tr) that 
> is not correctly accessed in a private function (mypltr) of the x09f 
> program. Here is what gdb tells me:
>
>    $ gdb x09f
>    […]
>    (gdb) run -dev ps -o /dev/null
>    Starting program: /home/rafael/fortran/x09f -dev ps -o /dev/null
>    [Thread debugging using libthread_db enabled]
>    Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".
>
>    Program received signal SIGBUS, Bus error.
>    0x00400dfe in x09f::mypltr (x=0, y=1, xt=1, yt=34) at x09f.f90:193
>    193             xt = tr(1) * x + tr(2) * y + tr(3)
>
> My knowledge of Fortran and gfortran is way too scarce and, therefore, I 
> cannot debug the problem deeper.  There may be a programming error in 
> x09f.f90 or this may be a problem with gfortran on armhf when option 
> -fstack-clash-protection is given.
>
> Any help will be appreciated.
>
> Best,
>
> Rafael Laboissière

Attachment: bug-1055750.tgz
Description: application/gtar-compressed