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, 126 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/xtensa/__longjmp.S b/libc/sysdeps/linux/xtensa/__longjmp.S
new file mode 100644
index 000000000..0fa939095
--- /dev/null
+++ b/libc/sysdeps/linux/xtensa/__longjmp.S
@@ -0,0 +1,126 @@
+/* longjmp 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"
+
+
+ENTRY (__longjmp)
+
+	/* Invalidate all but the current window.  Reading and writing
+	   special registers WINDOWBASE and WINDOWSTART are
+	   privileged operations, so user processes must call the
+	   slower __window_spill() to do the job.  */
+
+	movi	a4, __window_spill
+	callx4	a4
+
+	/* Return to the return address of the setjmp, using the
+	   window size bits from the setjmp call so that the caller
+	   will be able to find the return value that we put in a2.  */
+
+	l32i	a0, a2, 64
+
+	/* Copy the first 4 saved registers from jmp_buf into the save area
+	   at the current sp so that the values will be restored to registers
+	   when longjmp returns. */
+
+	addi	a7, a1, -16
+	l32i	a4, a2, 0
+	l32i	a5, a2, 4
+	s32i	a4, a7, 0
+	s32i	a5, a7, 4
+	l32i	a4, a2, 8
+	l32i	a5, a2, 12
+	s32i	a4, a7, 8
+	s32i	a5, a7, 12
+
+	/* Copy the remaining 0-8 saved registers.  */
+	extui	a7, a0, 30, 2
+	blti	a7, 2, .Lendlj
+	l32i	a8, a2, 52
+	slli	a4, a7, 4
+	sub	a6, a8, a4
+	addi	a5, a2, 16
+	addi	a8, a8, -16		// a8 = end of register overflow area
+.Lljloop:
+	l32i	a7, a5, 0
+	l32i	a4, a5, 4
+	s32i	a7, a6, 0
+	s32i	a4, a6, 4
+	l32i	a7, a5, 8
+	l32i	a4, a5, 12
+	s32i	a7, a6, 8
+	s32i	a4, a6, 12
+	addi	a5, a5, 16
+	addi	a6, a6, 16
+	blt	a6, a8, .Lljloop
+.Lendlj:
+
+	/* The 4 words saved from the register save area at the target's
+	   sp are copied back to the target procedure's save area.  The
+	   only point of this is to prevent a catastrophic failure in
+	   case the contents were moved by an alloca after calling
+	   setjmp.  This is a bit paranoid but it doesn't cost much.  */
+
+	l32i	a7, a2, 4		// load the target stack pointer
+	addi	a7, a7, -16		// find the destination save area
+	l32i	a4, a2, 48
+	l32i	a5, a2, 52
+	s32i	a4, a7, 0
+	s32i	a5, a7, 4
+	l32i	a4, a2, 56
+	l32i	a5, a2, 60
+	s32i	a4, a7, 8
+	s32i	a5, a7, 12
+
+	/* Return v ? v : 1.  */
+	movi	a2, 1
+	movnez	a2, a3, a3
+
+	retw
+END (__longjmp)
+
+libc_hidden_def (__longjmp)