[Intel-gfx] [PATCH igt 02/10] igt/gem_mmap_gtt: Simulate gdb inspecting a GTT mmap using ptrace()

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-07-31 10:41:06)
> 
> On 28/07/2017 13:08, Chris Wilson wrote:
> > gdb uses ptrace() to peek and poke bytes of the target's address space.
> > The kernel must implement an vm_ops->access() handler or else gdb will
> > be unable to inspect the pointer and report it as out-of-bounds. Worse
> > than useless as it causes immediate suspicion of the valid GTT pointer.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >   tests/gem_mmap_gtt.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 79 insertions(+)
> > 
> > diff --git a/tests/gem_mmap_gtt.c b/tests/gem_mmap_gtt.c
> > index 4ff5e7f1..61c08406 100644
> > --- a/tests/gem_mmap_gtt.c
> > +++ b/tests/gem_mmap_gtt.c
> > @@ -36,6 +36,8 @@
> >   #include <errno.h>
> >   #include <sys/stat.h>
> >   #include <sys/ioctl.h>
> > +#include <sys/ptrace.h>
> > +#include <sys/wait.h>
> >   #include "drm.h"
> >   
> >   #include "igt.h"
> > @@ -310,6 +312,81 @@ test_write_gtt(int fd)
> >       munmap(src, OBJECT_SIZE);
> >   }
> >   
> > +static void *memchr_inv(const void *s, int c, size_t n)
> > +{
> > +     const uint8_t *us = s;
> > +     const uint8_t uc = c;
> > +
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wcast-qual"
> > +     while (n--) {
> > +             if (*us != uc)
> > +                     return (void *) us;
> > +             us++;
> > +     }
> > +#pragma GCC diagnostic pop
> 
> Stripping away constness wouldn't work with a simpler:

Or just saying const void *memchr_inv().

In this case we don't need memchr_inv, as just a bool will do,
so memchr_eq().

> 
> uint8_t *us = (uint8_t *)s?
> 
> > +
> > +     return NULL;
> > +}
> > +
> > +static void
> > +test_ptrace(int fd)
> > +{
> > +     long AA, CC;
> > +     long *gtt, *copy;
> > +     uint32_t bo;
> > +     pid_t pid;
> > +
> > +     memset(&AA, 0xaa, sizeof(AA));
> > +     memset(&CC, 0x55, sizeof(CC));
> > +
> > +     copy = malloc(OBJECT_SIZE);
> > +     memset(copy, AA, OBJECT_SIZE);
> > +
> > +     bo = gem_create(fd, OBJECT_SIZE);
> > +     gtt = mmap_bo(fd, bo);
> > +     memset(gtt, CC, OBJECT_SIZE);
> > +     gem_close(fd, bo);
> > +
> > +     igt_assert(!memchr_inv(gtt, CC, OBJECT_SIZE));
> > +     igt_assert(!memchr_inv(copy, AA, OBJECT_SIZE));
> > +
> > +     switch ((pid = fork())) {
> > +             case -1:
> > +                     igt_assert(pid != -1);
> > +                     break;
> > +
> > +             case 0:
> > +                     ptrace(PTRACE_TRACEME, 0, NULL, NULL);
> > +                     raise(SIGSTOP);
> > +                     raise(SIGKILL);
> > +                     exit(0);
> > +                     break;
> > +
> > +             default:
> > +                     /* Wait for the child to ready themselves */
> > +                     wait(NULL);
> > +
> > +                     ptrace(PTRACE_ATTACH, pid, NULL, NULL);
> > +                     for (int i = 0; i < OBJECT_SIZE/sizeof(long); i++) {
> > +                             copy[i] = ptrace(PTRACE_PEEKDATA, pid, gtt+i, NULL);
> > +                             ptrace(PTRACE_POKEDATA, pid, gtt + i, AA);
> 
> Inconsistent whitespace in the above three lines. First and second need 
> a tidy.

? The whitespace carries meaning for me.