tests/tcg: Check that shmat() does not break /proc/self/maps

Add a regression test for a recently fixed issue, where shmat()
desynced the guest and the host view of the address space and caused
open("/proc/self/maps") to SEGV.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <jwyuvao4apydvykmsnvacwshdgy3ixv7qvkh4dbxm3jkwgnttw@k4wpaayou7oq>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tests/tcg/multiarch/linux/linux-shmat-maps.c

@@ -0,0 +1,55 @@
+/*
+ * Test that shmat() does not break /proc/self/maps.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <assert.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <unistd.h>
+
+int main(void)
+{
+    char buf[128];
+    int err, fd;
+    int shmid;
+    ssize_t n;
+    void *p;
+
+    shmid = shmget(IPC_PRIVATE, 1, IPC_CREAT | 0600);
+    assert(shmid != -1);
+
+    /*
+     * The original bug required a non-NULL address, which skipped the
+     * mmap_find_vma step, which could result in a host mapping smaller
+     * than the target mapping.  Choose an address at random.
+     */
+    p = shmat(shmid, (void *)0x800000, SHM_RND);
+    if (p == (void *)-1) {
+        /*
+         * Because we are now running the testcase for all guests for which
+         * we have a cross-compiler, the above random address might conflict
+         * with the guest executable in some way.  Rather than stopping,
+         * continue with a system supplied address, which should never fail.
+         */
+        p = shmat(shmid, NULL, 0);
+        assert(p != (void *)-1);
+    }
+
+    fd = open("/proc/self/maps", O_RDONLY);
+    assert(fd != -1);
+    do {
+        n = read(fd, buf, sizeof(buf));
+        assert(n >= 0);
+    } while (n != 0);
+    close(fd);
+
+    err = shmdt(p);
+    assert(err == 0);
+    err = shmctl(shmid, IPC_RMID, NULL);
+    assert(err == 0);
+
+    return EXIT_SUCCESS;
+}