Re: [PATCH 3/3] tests/tcg/s390x: Test BRASL and BRCL with large negative offsets

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

On Fri, 2022-03-11 at 19:57 +0100, David Hildenbrand wrote:
> On 11.03.22 19:49, Ilya Leoshkevich wrote:
> > Add a small test in order to prevent regressions.
> > 
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
> >  tests/tcg/s390x/Makefile.target        |  1 +
> >  tests/tcg/s390x/branch-relative-long.c | 29
> > ++++++++++++++++++++++++++
> >  2 files changed, 30 insertions(+)
> >  create mode 100644 tests/tcg/s390x/branch-relative-long.c
> > 
> > diff --git a/tests/tcg/s390x/Makefile.target
> > b/tests/tcg/s390x/Makefile.target
> > index 257c568c58..fd34b130f7 100644
> > --- a/tests/tcg/s390x/Makefile.target
> > +++ b/tests/tcg/s390x/Makefile.target
> > @@ -15,6 +15,7 @@ TESTS+=mvc
> >  TESTS+=shift
> >  TESTS+=trap
> >  TESTS+=signals-s390x
> > +TESTS+=branch-relative-long
> >  
> >  ifneq ($(HAVE_GDB_BIN),)
> >  GDB_SCRIPT=$(SRC_PATH)/tests/guest-debug/run-test.py
> > diff --git a/tests/tcg/s390x/branch-relative-long.c
> > b/tests/tcg/s390x/branch-relative-long.c
> > new file mode 100644
> > index 0000000000..b9fcee9873
> > --- /dev/null
> > +++ b/tests/tcg/s390x/branch-relative-long.c
> > @@ -0,0 +1,29 @@
> > +#include <assert.h>
> > +#include <stddef.h>
> > +#include <sys/mman.h>
> > +
> > +int main(void)
> > +{
> > +    const unsigned short opcodes[] = {
> > +        0xc005,  /* brasl %r0 */
> > +        0xc0f4,  /* brcl 0xf */
> > +    };
> > +    size_t length = 0x100000006;
> > +    unsigned char *buf;
> > +    int i;
> > +
> > +    buf = mmap(NULL, length, PROT_READ | PROT_WRITE | PROT_EXEC,
> > +               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> > +    assert(buf != MAP_FAILED);
> > +
> > +    *(unsigned short *)&buf[0] = 0x07fe;  /* br %r14 */
> > +    *(unsigned int *)&buf[0x100000002] = 0x80000000;
> > +    for (i = 0; i < sizeof(opcodes) / sizeof(opcodes[0]); i++) {
> > +        *(unsigned short *)&buf[0x100000000] = opcodes[i];
> > +        ((void (*)(void))&buf[0x100000000])();
> > +    }
> 
> Hmmm, can't we write some "nice" inline asm instead?
> 
> 

If we do this in a straightforward way, then the resulting binary will
be 4G large.

But maybe there is a way to play games with sections, I'll need to
think about it.