[PATCH] Add __enable_execute_stack() if required

[Christian Franke <Christian.Franke@t-online.de>]

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Some gcc versions generate a call to __enable_execute_stack() in 
trampolines for nested functions. This is the case for new Cygwin gcc-4.3.2.

Other GRUB2 target platforms may be affected - the following files in 
'gcc-4.3.2/gcc/config' source directory contains implementations of this 
function for libgcc:

alpha/osf.h
darwin.h
netbsd.h
openbsd.h
sol2.h
sparc/freebsd.h

This patch adds a dummy version of this function if necessary.

Christian

2008-09-16  Christian Franke  <franke@computer.org>

	* aclocal.m4 (grub_CHECK_ENABLE_EXECUTE_STACK): New function.
	* configure.ac: Call grub_CHECK_ENABLE_EXECUTE_STACK.
	* include/grub/misc.h [NEED_ENABLE_EXECUTE_STACK]:
	Export __enable_execute_stack() to modules.
	* kern/misc.c [NEED_ENABLE_EXECUTE_STACK] (__enable_execute_stack):
	New function.



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diff --git a/aclocal.m4 b/aclocal.m4
index ee6c4db..7be8d3b 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -379,6 +379,33 @@ dnl So use regparm 2 until a better test is found.
 	[Catch gcc bug])
 fi
 ])
+
+dnl Check if the C compiler generates calls to `__enable_execute_stack()'.
+AC_DEFUN(grub_CHECK_ENABLE_EXECUTE_STACK,[
+AC_MSG_CHECKING([whether `$CC' generates calls to `__enable_execute_stack()'])
+AC_LANG_CONFTEST([[
+void f (int (*p) (void));
+void g (int i)
+{
+  int nestedfunc (void) { return i; }
+  f (nestedfunc);
+}
+]])
+if AC_TRY_COMMAND([${CC-cc} ${CFLAGS} -S conftest.c]) && test -s conftest.s; then
+  true
+else
+  AC_MSG_ERROR([${CC-cc} failed to produce assembly code])
+fi
+if grep __enable_execute_stack conftest.s >/dev/null 2>&1; then
+  AC_DEFINE([NEED_ENABLE_EXECUTE_STACK], 1,
+	    [Define to 1 if GCC generates calls to __enable_execute_stack()])
+  AC_MSG_RESULT([yes])
+else
+  AC_MSG_RESULT([no])
+fi
+rm -f conftest*
+])
+
 \f
 dnl Check if the C compiler supports `-fstack-protector'.
 AC_DEFUN(grub_CHECK_STACK_PROTECTOR,[
diff --git a/configure.ac b/configure.ac
index c367454..2b0d146 100644
--- a/configure.ac
+++ b/configure.ac
@@ -305,6 +305,9 @@ fi
 # Compiler features.
 #
 
+# Need __enable_execute_stack() for nested function trampolines?
+grub_CHECK_ENABLE_EXECUTE_STACK
+
 # Smashing stack protector.
 grub_CHECK_STACK_PROTECTOR
 # Need that, because some distributions ship compilers that include
diff --git a/include/grub/misc.h b/include/grub/misc.h
index 3d89a60..15c18f5 100644
--- a/include/grub/misc.h
+++ b/include/grub/misc.h
@@ -82,6 +82,10 @@ grub_ssize_t EXPORT_FUNC(grub_utf8_to_ucs4) (grub_uint32_t *dest,
 grub_uint64_t EXPORT_FUNC(grub_divmod64) (grub_uint64_t n,
 					  grub_uint32_t d, grub_uint32_t *r);
 
+#ifdef NEED_ENABLE_EXECUTE_STACK
+void EXPORT_FUNC(__enable_execute_stack) (void *addr);
+#endif
+
 /* Inline functions.  */
 
 static inline unsigned int
diff --git a/kern/misc.c b/kern/misc.c
index bec6ebd..635eb72 100644
--- a/kern/misc.c
+++ b/kern/misc.c
@@ -1036,3 +1036,12 @@ grub_abort (void)
 }
 /* GCC emits references to abort().  */
 void abort (void) __attribute__ ((alias ("grub_abort")));
+
+#ifdef NEED_ENABLE_EXECUTE_STACK
+/* Some gcc versions generate a call to this function
+   in trampolines for nested functions.  */
+__enable_execute_stack (void *addr __attribute__ ((unused)))
+{
+}
+#endif
+