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, 103 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/x86_64/setcontext.S b/libc/sysdeps/linux/x86_64/setcontext.S
new file mode 100644
index 000000000..561ab9f75
--- /dev/null
+++ b/libc/sysdeps/linux/x86_64/setcontext.S
@@ -0,0 +1,103 @@
+/* Install given context.
+   Copyright (C) 2002-2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Andreas Jaeger <aj@suse.de>, 2002.
+
+   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"
+
+
+/*  int __setcontext (const ucontext_t *ucp)
+
+  Restores the machine context in UCP and thereby resumes execution
+  in that context.
+
+  This implementation is intended to be used for *synchronous* context
+  switches only.  Therefore, it does not have to restore anything
+  other than the PRESERVED state.  */
+
+ENTRY(__setcontext)
+	/* Save argument since syscall will destroy it.  */
+	pushq	%rdi
+	cfi_adjust_cfa_offset(8)
+
+	/* Set the signal mask with
+	   rt_sigprocmask (SIG_SETMASK, mask, NULL, _NSIG/8).  */
+	leaq	oSIGMASK(%rdi), %rsi
+	xorl	%edx, %edx
+	movl	$SIG_SETMASK, %edi
+	movl	$_NSIG8,%r10d
+	movl	$__NR_rt_sigprocmask, %eax
+	syscall
+	popq	%rdi			/* Reload %rdi, adjust stack.  */
+	cfi_adjust_cfa_offset(-8)
+	cmpq	$-4095, %rax		/* Check %rax for error.  */
+	jae	SYSCALL_ERROR_LABEL	/* Jump to error handler if error.  */
+
+	/* Restore the floating-point context.  Not the registers, only the
+	   rest.  */
+	movq	oFPREGS(%rdi), %rcx
+	fldenv	(%rcx)
+	ldmxcsr oMXCSR(%rdi)
+
+
+	/* Load the new stack pointer, the preserved registers and
+	   registers used for passing args.  */
+	cfi_def_cfa(%rdi, 0)
+	cfi_offset(%rbx,oRBX)
+	cfi_offset(%rbp,oRBP)
+	cfi_offset(%r12,oR12)
+	cfi_offset(%r13,oR13)
+	cfi_offset(%r14,oR14)
+	cfi_offset(%r15,oR15)
+	cfi_offset(%rsp,oRSP)
+	cfi_offset(%rip,oRIP)
+
+	movq	oRSP(%rdi), %rsp
+	movq	oRBX(%rdi), %rbx
+	movq	oRBP(%rdi), %rbp
+	movq	oR12(%rdi), %r12
+	movq	oR13(%rdi), %r13
+	movq	oR14(%rdi), %r14
+	movq	oR15(%rdi), %r15
+
+	/* The following ret should return to the address set with
+	getcontext.  Therefore push the address on the stack.  */
+	movq	oRIP(%rdi), %rcx
+	pushq	%rcx
+
+	movq	oRSI(%rdi), %rsi
+	movq	oRDX(%rdi), %rdx
+	movq	oRCX(%rdi), %rcx
+	movq	oR8(%rdi), %r8
+	movq	oR9(%rdi), %r9
+
+	/* Setup finally  %rdi.  */
+	movq	oRDI(%rdi), %rdi
+
+	/* End FDE here, we fall into another context.  */
+	cfi_endproc
+	cfi_startproc
+
+	/* Clear rax to indicate success.  */
+	xorl	%eax, %eax
+L(pseudo_end):
+	ret
+PSEUDO_END(__setcontext)
+
+weak_alias (__setcontext, setcontext)