Chris Zankel writes:

The following patches add support for the Xtensa processor architecture
to uClibc. They are based on a recent SVN checkout (12/05/2007).

The first patch (attached to this post) adds Xtensa support to various
shared configuration and make files. The following patches then include
the Xtensa specific files and directories.

I welcome any feedback and would appreciate it if you could include the
patches into the mainline tree. I am certainly committed to maintain the port. 

Bob Wilson was kind enough to review the patches.

Some notes about the architecture: Xtensa is a configurable and
extensible processor architecture developed by Tensilica. For more
information, please visit: www.linux-xtensa.org.

1 files changed, 131 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/xtensa/setjmp.S b/libc/sysdeps/linux/xtensa/setjmp.S
new file mode 100644
index 000000000..5e81460c7
--- /dev/null
+++ b/libc/sysdeps/linux/xtensa/setjmp.S
@@ -0,0 +1,131 @@
+/* setjmp for Xtensa Processors.
+   Copyright (C) 2001, 2007 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, write to the Free
+   Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+   Boston, MA 02110-1301, USA.  */
+
+/* This implementation relies heavily on the Xtensa register window
+   mechanism.  Setjmp flushes all the windows except its own to the
+   stack and then copies registers from the save areas on the stack
+   into the jmp_buf structure, along with the return address of the call
+   to setjmp.  Longjmp invalidates all the windows except its own, and
+   then sets things up so that it will return to the right place,
+   using a window underflow to automatically restore the registers.
+
+   Note that it would probably be sufficient to only copy the
+   registers from setjmp's caller into jmp_buf.  However, we also copy
+   the save area located at the stack pointer of setjmp's caller.
+   This save area will typically remain intact until the longjmp call.
+   The one exception is when there is an intervening alloca in
+   setjmp's caller.  This is certainly an unusual situation and is
+   likely to cause problems in any case (the storage allocated on the
+   stack cannot be safely accessed following the longjmp).  As bad as
+   it is, on most systems this situation would not necessarily lead to
+   a catastrophic failure.  If we did not preserve the extra save area
+   on Xtensa, however, it would.  When setjmp's caller returns after a
+   longjmp, there will be a window underflow; an invalid return
+   address or stack pointer in the save area will almost certainly
+   lead to a crash.  Keeping a copy of the extra save area in the
+   jmp_buf avoids this with only a small additional cost.  If setjmp
+   and longjmp are ever time-critical, this could be removed.  */
+
+#include "sysdep.h"
+
+/* int setjmp (a2 = jmp_buf env) */
+
+ENTRY (_setjmp)
+	movi	a3, 0
+	j	1f
+END (_setjmp)
+libc_hidden_def (_setjmp)
+
+ENTRY (setjmp)
+	movi	a3, 1
+	j	1f
+END (setjmp)
+
+/* int __sigsetjmp (a2 = jmp_buf env,
+		    a3 = int savemask)  */
+
+ENTRY (__sigsetjmp)
+1:	
+	/* Flush registers.  */
+	movi	a4, __window_spill
+	callx4	a4
+
+	/* Preserve the second argument (savemask) in a15.  The selection
+ 	   of a15 is arbitrary, except it's otherwise unused.  There is no
+	   risk of triggering a window overflow since we just returned
+	   from __window_spill().  */
+	mov	a15, a3
+
+	/* Copy the register save area at (sp - 16).  */
+	addi	a5, a1, -16
+	l32i	a3, a5, 0
+	l32i	a4, a5, 4
+	s32i	a3, a2, 0
+	s32i	a4, a2, 4
+	l32i	a3, a5, 8
+	l32i	a4, a5, 12
+	s32i	a3, a2, 8
+	s32i	a4, a2, 12
+
+	/* Copy 0-8 words from the register overflow area.  */
+	extui	a3, a0, 30, 2
+	blti	a3, 2, .Lendsj
+	l32i	a7, a1, 4
+	slli	a4, a3, 4
+	sub	a5, a7, a4
+	addi	a6, a2, 16
+	addi	a7, a7, -16		// a7 = end of register overflow area
+.Lsjloop:
+	l32i	a3, a5, 0
+	l32i	a4, a5, 4
+	s32i	a3, a6, 0
+	s32i	a4, a6, 4
+	l32i	a3, a5, 8
+	l32i	a4, a5, 12
+	s32i	a3, a6, 8
+	s32i	a4, a6, 12
+	addi	a5, a5, 16
+	addi	a6, a6, 16
+	blt	a5, a7, .Lsjloop
+.Lendsj:
+
+	/* Copy the register save area at sp.  */
+	l32i	a3, a1, 0
+	l32i	a4, a1, 4
+	s32i	a3, a2, 48
+	s32i	a4, a2, 52
+	l32i	a3, a1, 8
+	l32i	a4, a1, 12
+	s32i	a3, a2, 56
+	s32i	a4, a2, 60
+
+	/* Save the return address, including the window size bits.  */
+	s32i	a0, a2, 64
+
+	/* a2 still addresses jmp_buf.  a15 contains savemask.  */
+	mov	a6, a2
+	mov	a7, a15
+	movi	a3, __sigjmp_save
+	callx4	a3
+	mov	a2, a6
+	retw
+END(__sigsetjmp)
+
+weak_extern(_setjmp)
+weak_extern(setjmp)