libc: add {get,set,swap,make}context user context manipulation functions

Add the obsolescent SUSv3 family of user context manipulating functions
for arm, i386, mips, x86_64.

Signed-off-by: Timon ter Braak <timonterbraak@gmail.com>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

1 files changed, 110 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/i386/swapcontext.S b/libc/sysdeps/linux/i386/swapcontext.S
new file mode 100644
index 000000000..ee5d0e4d5
--- /dev/null
+++ b/libc/sysdeps/linux/i386/swapcontext.S
@@ -0,0 +1,110 @@
+/* Save current context and install the given one.
+   Copyright (C) 2001-2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2001.
+
+   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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+#include "ucontext_i.h"
+
+
+ENTRY(__swapcontext)
+	/* Load address of the context data structure we save in.  */
+	movl	4(%esp), %eax
+
+	/* Return value of swapcontext.  EAX is the only register whose
+	   value is not preserved.  */
+	movl	$0, oEAX(%eax)
+
+	/* Save the 32-bit register values and the return address.  */
+	movl	%ecx, oECX(%eax)
+	movl	%edx, oEDX(%eax)
+	movl	%edi, oEDI(%eax)
+	movl	%esi, oESI(%eax)
+	movl	%ebp, oEBP(%eax)
+	movl	(%esp), %ecx
+	movl	%ecx, oEIP(%eax)
+	leal	4(%esp), %ecx
+	movl	%ecx, oESP(%eax)
+	movl	%ebx, oEBX(%eax)
+
+	/* Save the FS segment register.  */
+	xorl	%edx, %edx
+	movw	%fs, %dx
+	movl	%edx, oFS(%eax)
+
+	/* We have separate floating-point register content memory on the
+	   stack.  We use the __fpregs_mem block in the context.  Set the
+	   links up correctly.  */
+	leal	oFPREGSMEM(%eax), %ecx
+	movl	%ecx, oFPREGS(%eax)
+	/* Save the floating-point context.  */
+	fnstenv	(%ecx)
+
+	/* Load address of the context data structure we have to load.  */
+	movl	8(%esp), %ecx
+
+	/* Save the current signal mask and install the new one.  */
+	pushl	%ebx
+	leal	oSIGMASK(%eax), %edx
+	leal	oSIGMASK(%ecx), %ecx
+	movl	$SIG_SETMASK, %ebx
+	movl	$__NR_sigprocmask, %eax
+	ENTER_KERNEL
+	popl	%ebx
+	cmpl	$-4095, %eax		/* Check %eax for error.  */
+	jae	SYSCALL_ERROR_LABEL	/* Jump to error handler if error.  */
+
+	/* EAX was modified, reload it.  */
+	movl	8(%esp), %eax
+
+	/* Restore the floating-point context.  Not the registers, only the
+	   rest.  */
+	movl	oFPREGS(%eax), %ecx
+	fldenv	(%ecx)
+
+	/* Restore the FS segment register.  We don't touch the GS register
+	   since it is used for threads.  */
+	movl	oFS(%eax), %edx
+	movw	%dx, %fs
+
+	/* Fetch the address to return to.  */
+	movl	oEIP(%eax), %ecx
+
+	/* Load the new stack pointer.  */
+	movl	oESP(%eax), %esp
+
+	/* Push the return address on the new stack so we can return there.  */
+	pushl	%ecx
+
+	/* Load the values of all the 32-bit registers (except ESP).
+	   Since we are loading from EAX, it must be last.  */
+	movl	oEDI(%eax), %edi
+	movl	oESI(%eax), %esi
+	movl	oEBP(%eax), %ebp
+	movl	oEBX(%eax), %ebx
+	movl	oEDX(%eax), %edx
+	movl	oECX(%eax), %ecx
+	movl	oEAX(%eax), %eax
+
+	/* The following 'ret' will pop the address of the code and jump
+	   to it.  */
+L(pseudo_end):
+	ret
+PSEUDO_END(__swapcontext)
+
+weak_alias (__swapcontext, swapcontext)