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 <ch...@chris-wilson.co.uk>
---
tests/i915/gem_mmap_gtt.c | 79 ++++++++++++++++++++++++++++++++++++++-
1 file changed, 78 insertions(+), 1 deletion(-)
diff --git a/tests/i915/gem_mmap_gtt.c b/tests/i915/gem_mmap_gtt.c
index 1f4655af4..38b4d02d7 100644
--- a/tests/i915/gem_mmap_gtt.c
+++ b/tests/i915/gem_mmap_gtt.c
@@ -34,8 +34,11 @@
#include <inttypes.h>
#include <pthread.h>
#include <errno.h>
-#include <sys/stat.h>
+#include <signal.h>
#include <sys/ioctl.h>
+#include <sys/ptrace.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
#include "drm.h"
#include "igt.h"
@@ -501,6 +504,78 @@ 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
+
+ return NULL;
+}
+
+static void
+test_ptrace(int fd)
+{
+ unsigned long AA, CC;
+ unsigned long *gtt, *cpy;
+ uint32_t bo;
+ pid_t pid;
+
+ memset(&AA, 0xaa, sizeof(AA));
+ memset(&CC, 0x55, sizeof(CC));
+
+ cpy = malloc(OBJECT_SIZE);
+ memset(cpy, AA, OBJECT_SIZE);
+
+ bo = gem_create(fd, OBJECT_SIZE);
+ gtt = mmap_bo(fd, bo, OBJECT_SIZE);
+ memset(gtt, CC, OBJECT_SIZE);
+ gem_close(fd, bo);
+
+ igt_assert(!memchr_inv(gtt, CC, OBJECT_SIZE));
+ igt_assert(!memchr_inv(cpy, AA, OBJECT_SIZE));
+
+ igt_fork(child, 1) {
+ ptrace(PTRACE_TRACEME, 0, NULL, NULL);
+ raise(SIGSTOP);
+ }
+
+ /* Wait for the child to ready themselves [SIGSTOP] */
+ pid = wait(NULL);
+
+ ptrace(PTRACE_ATTACH, pid, NULL, NULL);
+ for (int i = 0; i < OBJECT_SIZE / sizeof(long); i++) {
+ long ret;
+
+ ret = ptrace(PTRACE_PEEKDATA, pid, gtt + i);
+ igt_assert_eq_u64(ret, CC);
+ cpy[i] = ret;
+
+ ret = ptrace(PTRACE_POKEDATA, pid, gtt + i, AA);
+ igt_assert_eq(ret, 0l);
+ }
+ ptrace(PTRACE_DETACH, pid, NULL, NULL);
+
+ /* Wakeup the child for it to exit */
+ kill(SIGCONT, pid);
+ igt_waitchildren();
+
+ /* The contents of the two buffers should now be swapped */
+ igt_assert(!memchr_inv(gtt, AA, OBJECT_SIZE));
+ igt_assert(!memchr_inv(cpy, CC, OBJECT_SIZE));
+
+ munmap(gtt, OBJECT_SIZE);
+ free(cpy);
+}
+
static bool is_coherent(int i915)
{
int val = 1; /* by default, we assume GTT is coherent, hence the test */
@@ -1084,6 +1159,8 @@ igt_main
test_write(fd);
igt_subtest("basic-write-gtt")
test_write_gtt(fd);
+ igt_subtest("ptrace")
+ test_ptrace(fd);
igt_subtest("coherency")
test_coherency(fd);
igt_subtest("clflush")
--
2.26.2
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