aarch64: morello: add purecap ld.so _start code

The purecap version of aarch64 dl-start.S. Note: self relocation of
ld.so is handled by the rtld bootstrap code.

The ldso internal _dl_start still expects continuous argc, argv, envp,
auxv, so that's emulated (since the purecap ELF entry passes them in
separate registers).

1 files changed, 110 insertions, 0 deletions

diff --git a/sysdeps/aarch64/morello/dl-start.c b/sysdeps/aarch64/morello/dl-start.c
new file mode 100644
index 0000000..f1b792d
--- /dev/null
+++ b/sysdeps/aarch64/morello/dl-start.c
@@ -0,0 +1,110 @@
+/* ld.so _start code.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <assert.h>
+#include <ldsodefs.h>
+
+asm(""
+".global	_start\n"
+".type		_start, %function\n"
+"_start:\n"
+"	.cfi_startproc\n"
+"	.cfi_undefined c30\n"
+"	mov	c29, czr\n"
+"	mov	c30, czr\n"
+"	b	__real_start\n"
+"	.cfi_endproc\n"
+"	.size _start, .-_start\n");
+
+typedef void (entry_t) (int, char **, char **, void *, void (*)(void));
+
+__attribute__ ((noinline, noreturn))
+void
+_dl_start_user (uintptr_t *args, entry_t *entry)
+{
+  /* Setup argv, envp, auxv for the application.  */
+  uintptr_t *p;
+  long n;
+  int argc = args[0];
+  p = args + 1;
+  n = argc + 1;
+  char **argv = (char **) __builtin_cheri_bounds_set (p, n * sizeof *p);
+  p += n;
+  for (n = 0; p[n]; n++);
+  n++;
+  char **envp = (char **) __builtin_cheri_bounds_set (p, n * sizeof *p);
+  p += n;
+  for (n = 0; p[n] != AT_NULL; n += 2);
+  n += 2;
+  uintptr_t *auxv = __builtin_cheri_bounds_set (p, n * sizeof *p);
+
+  _dl_init (GL(dl_ns)[LM_ID_BASE]._ns_loaded, argc, argv, envp);
+  entry (argc, argv, envp, auxv, _dl_fini);
+  __builtin_trap ();
+}
+
+/* Count the array length needed for traditional ELF entry.  */
+static inline long
+count_args (int argc, char **argv, char **envp, uintptr_t *auxv)
+{
+  char **p;
+  uintptr_t *q;
+  long nargs = argc + 2;
+  for (p = envp; *p != NULL; p++);
+  nargs += p - envp + 1;
+  for (q = auxv; *q != AT_NULL; q += 2);
+  nargs += q - auxv + 2;
+  return nargs;
+}
+
+/* Generic ld.so start code in rtld.c.  */
+uintptr_t
+_dl_start (void *) attribute_hidden;
+
+/* ld.so entry point.  */
+void
+__real_start (int argc, char **argv, char **envp, void *auxv)
+{
+  long nargs = count_args (argc, argv, envp, auxv);
+  {
+    /* _dl_start requires continuous argv, envp, auxv.  */
+    uintptr_t args[nargs];
+    long i = 0, j;
+    args[i++] = argc;
+    for (j = 0; argv[j] != NULL; j++)
+      args[i++] = (uintptr_t) argv[j];
+    args[i++] = 0;
+    for (j = 0; envp[j] != NULL; j++)
+      args[i++] = (uintptr_t) envp[j];
+    args[i++] = 0;
+    uintptr_t *a = auxv;
+    for (j = 0; a[j] != AT_NULL; j += 2)
+      {
+	args[i++] = a[j];
+	args[i++] = a[j+1];
+      }
+    args[i++] = AT_NULL;
+    args[i++] = 0;
+    assert (i == nargs);
+
+    /* Run ls.so setup.  */
+    entry_t *entry = (entry_t *) _dl_start (args);
+    _dl_start_user (args, entry);
+  }
+}