[PATCH 2/2] New internal function __access_noerrno

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

This ia follow up patch for tunables requirement [1].  It Implement 
an internal version of __access called __access_noerrno that
avoids setting errno.  This is useful to check accessibility of files
very early on in process startup i.e. before TLS setup.  This allows
tunables to replace MALLOC_CHECK_ safely (i.e. check existence of
/etc/suid-debug to enable/disable MALLOC_CHECK) and at the same time
initialize very early so that it can override IFUNCs.

Checked on x86_64.

	Siddhesh Poyarekar  <siddhesh@sourceware.org>
	Adhemerval Zanella  <adhemerval.zanella@linaro.org>

	* hurd/hurd.h (__hurd_fail_noerrno): New function.
	* include/unistd.h [IS_IN (rtld) || !defined SHARED]: Declare
	__access_noerrno.
	* io/access.c (__access_noerrno): New function.
	* sysdeps/mach/hurd/access.c (hurd_fail_seterrno): New function.
	(hurd_fail_seterrno): Likewise.
	(access_common): Likewise.
	(__access_noerrno): Likewise.
	* sysdeps/nacl/access.c (__access_noerrno): Likewise.
	* sysdeps/unix/sysv/linux/access.c (__access_noerrno): Likewise.
	* sysdeps/nacl/nacl-interfaces.h (NACL_CALL_NOERRNO): New
	macro.

[1] https://sourceware.org/ml/libc-alpha/2016-11/msg00399.html
---
 ChangeLog                        | 13 +++++++++++++
 hurd/hurd.h                      | 30 ++++++++++++++++++++++++++++++
 include/unistd.h                 |  6 ++++++
 io/access.c                      |  8 +++++++-
 sysdeps/mach/hurd/access.c       | 37 +++++++++++++++++++++++++++++++------
 sysdeps/nacl/access.c            |  7 +++++++
 sysdeps/nacl/nacl-interfaces.h   |  4 ++++
 sysdeps/unix/sysv/linux/access.c | 15 +++++++++++++++
 8 files changed, 113 insertions(+), 7 deletions(-)

diff --git a/hurd/hurd.h b/hurd/hurd.h
index ec07827..8bcb1ec 100644
--- a/hurd/hurd.h
+++ b/hurd/hurd.h
@@ -75,6 +75,36 @@ __hurd_fail (error_t err)
   errno = err;
   return -1;
 }
+
+_HURD_H_EXTERN_INLINE int
+__hurd_fail_noerrno (error_t err)
+{
+  switch (err)
+    {
+    case EMACH_SEND_INVALID_DEST:
+    case EMIG_SERVER_DIED:
+      /* The server has disappeared!  */
+      err = EIEIO;
+      break;
+
+    case KERN_NO_SPACE:
+      err = ENOMEM;
+      break;
+
+    case KERN_INVALID_ARGUMENT:
+      err = EINVAL;
+      break;
+
+    case 0:
+      return 0;
+
+    default:
+      break;
+    }
+
+  errno = err;
+  return -1;
+}
 
 /* Basic ports and info, initialized by startup.  */
 
diff --git a/include/unistd.h b/include/unistd.h
index d2802b2..6144f41 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -181,6 +181,12 @@ extern int __getlogin_r_loginuid (char *name, size_t namesize)
 #   include <dl-unistd.h>
 #  endif
 
+#  if IS_IN (rtld) || !defined SHARED
+/* __access variant that does not set errno.  Used in very early initialization
+   code in libc.a and ld.so.  */
+extern __typeof (__access) __access_noerrno attribute_hidden;
+#  endif
+
 __END_DECLS
 # endif
 
diff --git a/io/access.c b/io/access.c
index 4534704..68b49ca 100644
--- a/io/access.c
+++ b/io/access.c
@@ -19,6 +19,13 @@
 #include <stddef.h>
 #include <unistd.h>
 
+/* Test for access to FILE without setting errno.   */
+int
+__access_noerrno (const char *file, int type)
+{
+  return -1;
+}
+
 /* Test for access to FILE.  */
 int
 __access (const char *file, int type)
@@ -33,5 +40,4 @@ __access (const char *file, int type)
   return -1;
 }
 stub_warning (access)
-
 weak_alias (__access, access)
diff --git a/sysdeps/mach/hurd/access.c b/sysdeps/mach/hurd/access.c
index c308340..620acea 100644
--- a/sysdeps/mach/hurd/access.c
+++ b/sysdeps/mach/hurd/access.c
@@ -22,9 +22,20 @@
 #include <hurd/lookup.h>
 #include <fcntl.h>
 
-/* Test for access to FILE by our real user and group IDs.  */
-int
-__access (const char *file, int type)
+static int
+hurd_fail_seterrno (error_t err)
+{
+  return __hurd_fail (err);
+}
+
+static int
+hurd_fail_noerrno (error_t err)
+{
+  return __hurd_fail_noerrno (err);
+}
+
+static int
+access_common (const char *file, int type, int (*errfunc) (error_t))
 {
   error_t err;
   file_t rcrdir, rcwdir, io;
@@ -120,13 +131,13 @@ __access (const char *file, int type)
   if (rcwdir != MACH_PORT_NULL)
     __mach_port_deallocate (__mach_task_self (), rcwdir);
   if (err)
-    return __hurd_fail (err);
+    return errfunc (err);
 
   /* Find out what types of access we are allowed to this file.  */
   err = __file_check_access (io, &allowed);
   __mach_port_deallocate (__mach_task_self (), io);
   if (err)
-    return __hurd_fail (err);
+    return errfunc (err);
 
   flags = 0;
   if (type & R_OK)
@@ -138,9 +149,23 @@ __access (const char *file, int type)
 
   if (flags & ~allowed)
     /* We are not allowed all the requested types of access.  */
-    return __hurd_fail (EACCES);
+    return errfunc (EACESS);
 
   return 0;
 }
 
+/* Test for access to FILE by our real user and group IDs without setting
+   errno.  */
+int
+__access_noerrno (const char *file, int type)
+{
+  return access_common (file, type, hurd_fail_noerrno);
+}
+
+/* Test for access to FILE by our real user and group IDs.  */
+int
+__access (const char *file, int type)
+{
+  return access_common (file, type, hurd_fail);
+}
 weak_alias (__access, access)
diff --git a/sysdeps/nacl/access.c b/sysdeps/nacl/access.c
index 95a0fb7..4266d63 100644
--- a/sysdeps/nacl/access.c
+++ b/sysdeps/nacl/access.c
@@ -19,6 +19,13 @@
 #include <unistd.h>
 #include <nacl-interfaces.h>
 
+/* Test for access to FILE without setting errno.  */
+int
+__access (const char *file, int type)
+{
+  return NACL_CALL_NOERRNO (__nacl_irt_dev_filename.access (file, type), 0);
+}
+
 /* Test for access to FILE.  */
 int
 __access (const char *file, int type)
diff --git a/sysdeps/nacl/nacl-interfaces.h b/sysdeps/nacl/nacl-interfaces.h
index b7b45bb..edd3217 100644
--- a/sysdeps/nacl/nacl-interfaces.h
+++ b/sysdeps/nacl/nacl-interfaces.h
@@ -113,4 +113,8 @@ __nacl_fail (int err)
 #define NACL_CALL(err, val) \
   ({ int _err = (err); _err ? __nacl_fail (_err) : (val); })
 
+/* Same as NACL_CALL but without setting errno.  */
+#define NACL_CALL_NOERRNO(err, val) \
+  ({ int _err = (err); _err ? _err : (val); })
+
 #endif  /* nacl-interfaces.h */
diff --git a/sysdeps/unix/sysv/linux/access.c b/sysdeps/unix/sysv/linux/access.c
index cdb7908..004da1b 100644
--- a/sysdeps/unix/sysv/linux/access.c
+++ b/sysdeps/unix/sysv/linux/access.c
@@ -19,6 +19,21 @@
 #include <unistd.h>
 #include <sysdep-cancel.h>
 
+int
+__access_noerro (const char *file, int type)
+{
+  int res;
+  INTERNAL_SYSCALL_DECL (err);
+#ifdef __NR_access
+  res = INTERNAL_SYSCALL_CALL (access, err, file, type);
+#else
+  res = INTERNAL_SYSCALL_CALL (faccessat, err, AT_FDCWD, file, type);
+#endif
+  if (INTERNAL_SYSCALL_ERROR_P (res, err))
+    return INTERNAL_SYSCALL_ERRNO (res, err);
+  return 0;
+}
+
 /* Test for access to FILE.  */
 int
 __access (const char *file, int type)
-- 
2.7.4