Re: [PATCH 2/2] tests/tcg/s390x: Test SIGILL handling

[Ilya Leoshkevich <iii@linux.ibm.com>]

On Fri, 2021-05-21 at 09:54 +0200, David Hildenbrand wrote:
> On 21.05.21 05:01, Ilya Leoshkevich wrote:
> > Verify that s390x-specific uc_mcontext.psw.addr is reported
> > correctly.
> > 
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
> >   tests/tcg/s390x/Makefile.target |  1 +
> >   tests/tcg/s390x/sigill.c        | 41
> > +++++++++++++++++++++++++++++++++
> >   2 files changed, 42 insertions(+)
> >   create mode 100644 tests/tcg/s390x/sigill.c
> > 
> > diff --git a/tests/tcg/s390x/Makefile.target
> > b/tests/tcg/s390x/Makefile.target
> > index 241ef28f61..8699d829a5 100644
> > --- a/tests/tcg/s390x/Makefile.target
> > +++ b/tests/tcg/s390x/Makefile.target
> > @@ -8,3 +8,4 @@ TESTS+=exrl-trtr
> >   TESTS+=pack
> >   TESTS+=mvo
> >   TESTS+=mvc
> > +TESTS+=sigill
> > diff --git a/tests/tcg/s390x/sigill.c b/tests/tcg/s390x/sigill.c
> > new file mode 100644
> > index 0000000000..f8021dc6af
> > --- /dev/null
> > +++ b/tests/tcg/s390x/sigill.c
> > @@ -0,0 +1,41 @@
> > +#include <assert.h>
> > +#include <signal.h>
> > +#include <string.h>
> > +#include <ucontext.h>
> > +#include <unistd.h>
> > +
> > +extern char expected_si_addr[];
> > +extern char expected_psw_addr[];
> 
> Why "extern" ? For the magic inline asm below to work?

Yes - it cannot be static, because AFAIK there is no such thing as
static variable declaration (one can only define static variables).

> > +
> > +static void handle_signal(int sig, siginfo_t *info, void
> > *ucontext)
> > +{
> > +    if (sig != SIGILL) {
> > +        _exit(1);
> > +    }
> > +
> > +    if (info->si_addr != expected_si_addr) {
> > +        _exit(2);
> > +    }
> > +
> > +    if (((ucontext_t *)ucontext)->uc_mcontext.psw.addr !=
> > +            (unsigned long)expected_psw_addr) {
> > +        _exit(3);
> > +    }
> > +}
> > +
> > +int main(void)
> > +{
> > +    struct sigaction act;
> > +
> > +    memset(&act, 0, sizeof(act));
> > +    act.sa_sigaction = handle_signal;
> > +    act.sa_flags = SA_SIGINFO;
> > +
> > +    int ret = sigaction(SIGILL, &act, NULL);
> 
> Mixing code and declaration.

Ouch, will fix.

> > +    assert(ret == 0);
> > +
> > +    asm volatile("expected_si_addr:\t.byte\t0x00,0x00\n"
> > +                 "expected_psw_addr:");
> 
> At least I am confused how the right values actually end up in 
> expected_si_addr and expected_psw_addr.
> 
> Can we maybe add a comment? This looks quite hacky ;)

This whole construction is roughly the same as having sigill.s file
with:

.globl expected_si_addr
expected_si_addr: .byte 0,0
.globl expected_psw_addr
expected_psw_addr: br 14

and sigill.h file with:

void expected_si_addr(void);
extern char expected_psw_addr[];

Doing it this way would complicate the build, so I thought it would be
better to just put everything into a single file.