csu: Implement and use _dl_early_allocate during static startup

This implements mmap fallback for a brk failure during TLS
allocation.

scripts/tls-elf-edit.py is updated to support the new patching method.
The script no longer requires that in the input object is of ET_DYN
type.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

2 files changed, 87 insertions, 0 deletions

diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 4a5e698..5d03693 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1211,6 +1211,11 @@ extern struct link_map * _dl_get_dl_main_map (void)
 # endif
 #endif
 
+/* Perform early memory allocation, avoding a TCB dependency.
+   Terminate the process if allocation fails.  May attempt to use
+   brk.  */
+void *_dl_early_allocate (size_t size) attribute_hidden;
+
 /* Initialize the DSO sort algorithm to use.  */
 #if !HAVE_TUNABLES
 static inline void
diff --git a/sysdeps/unix/sysv/linux/dl-early_allocate.c b/sysdeps/unix/sysv/linux/dl-early_allocate.c
new file mode 100644
index 0000000..52c538e
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/dl-early_allocate.c
@@ -0,0 +1,82 @@
+/* Early memory allocation for the dynamic loader.  Generic version.
+   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/>.  */
+
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
+#include <startup.h>
+
+#include <ldsodefs.h>
+#include <stddef.h>
+#include <string.h>
+#include <sysdep.h>
+#include <unistd.h>
+
+#include <brk_call.h>
+#include <mmap_call.h>
+
+/* Defined in brk.c.  */
+extern void *__curbrk;
+
+void *
+_dl_early_allocate (size_t size)
+{
+  void *result;
+
+  if (__curbrk != NULL)
+    /* If the break has been initialized, brk must have run before,
+       so just call it once more.  */
+    {
+      result = __sbrk (size);
+      if (result == (void *) -1)
+        result = NULL;
+    }
+  else
+    {
+      /* If brk has not been invoked, there is no need to update
+         __curbrk.  The first call to brk will take care of that.  */
+      void *previous = __brk_call (0);
+      result = __brk_call (previous + size);
+      if (result == previous)
+        result = NULL;
+      else
+        result = previous;
+    }
+
+  /* If brk fails, fall back to mmap.  This can happen due to
+     unfortunate ASLR layout decisions and kernel bugs, particularly
+     for static PIE.  */
+  if (result == NULL)
+    {
+      long int ret;
+      int prot = PROT_READ | PROT_WRITE;
+      int flags = MAP_PRIVATE | MAP_ANONYMOUS;
+#ifdef __NR_mmap2
+      ret = MMAP_CALL_INTERNAL (mmap2, 0, size, prot, flags, -1, 0);
+#else
+      ret = MMAP_CALL_INTERNAL (mmap, 0, size, prot, flags, -1, 0);
+#endif
+      if (INTERNAL_SYSCALL_ERROR_P (ret))
+        result = NULL;
+      else
+        result = (void *) ret;
+    }
+
+  return result;
+}