hurd: Add getcontext, makecontext, setcontext, swapcontext

Adapted from the Linux x86 functions.

Not thoroughly tested, but manual testing as well as glibc tests look fine, and
manual -lpthread testing also looks fine (within the given bounds for a new
stack to be used with makecontext).

This has also been in use in Debian since 2013.

1 files changed, 130 insertions, 0 deletions

diff --git a/sysdeps/mach/hurd/i386/makecontext.S b/sysdeps/mach/hurd/i386/makecontext.S
new file mode 100644
index 0000000000..e2f8afc895
--- /dev/null
+++ b/sysdeps/mach/hurd/i386/makecontext.S
@@ -0,0 +1,130 @@
+/* Create new context.
+   Copyright (C) 2001-2019 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+#include "ucontext_i.h"
+
+
+ENTRY(__makecontext)
+	movl	4(%esp), %eax
+
+	/* Load the address of the function we are supposed to run.  */
+	movl	8(%esp), %ecx
+
+	/* Compute the address of the stack.  The information comes from
+	   to us_stack element.  */
+	movl	oSS_SP(%eax), %edx
+	movl	%ecx, oEIP(%eax)
+	addl	oSS_SIZE(%eax), %edx
+
+	/* Remember the number of parameters for the exit handler since
+	   it has to remove them.  We store the number in the EBX register
+	   which the function we will call must preserve.  */
+	movl	12(%esp), %ecx
+	movl	%ecx, oEBX(%eax)
+
+	/* Make room on the new stack for the parameters.
+	   Room for the arguments, return address (== L(exitcode)) and
+	   oLINK pointer is needed.  One of the pointer sizes is subtracted
+	   after aligning the stack.  */
+	negl	%ecx
+	leal	-4(%edx,%ecx,4), %edx
+	negl	%ecx
+
+	/* Align the stack.  */
+	andl	$0xfffffff0, %edx
+	subl	$4, %edx
+
+	/* Store the future stack pointer.  */
+	movl	%edx, oESP(%eax)
+
+	/* Put the next context on the new stack (from the uc_link
+	   element).  */
+	movl	oLINK(%eax), %eax
+	movl	%eax, 4(%edx,%ecx,4)
+
+	/* Copy all the parameters.  */
+	jecxz	2f
+1:	movl	12(%esp,%ecx,4), %eax
+	movl	%eax, (%edx,%ecx,4)
+	decl	%ecx
+	jnz	1b
+2:
+
+	/* If the function we call returns we must continue with the
+	   context which is given in the uc_link element.  To do this
+	   set the return address for the function the user provides
+	   to a little bit of helper code which does the magic (see
+	   below).  */
+#ifdef PIC
+	call	1f
+	cfi_adjust_cfa_offset (4)
+1:	popl	%ecx
+	cfi_adjust_cfa_offset (-4)
+	addl	$L(exitcode)-1b, %ecx
+	movl	%ecx, (%edx)
+#else
+	movl	$L(exitcode), (%edx)
+#endif
+	/* We need to terminate the FDE here instead of after ret because
+	   the unwinder looks at ra-1 for unwind information.  */
+	cfi_endproc
+
+	/* 'makecontext' returns no value.  */
+	ret
+
+	/* This is the helper code which gets called if a function which
+	   is registered with 'makecontext' returns.  In this case we
+	   have to install the context listed in the uc_link element of
+	   the context 'makecontext' manipulated at the time of the
+	   'makecontext' call.  If the pointer is NULL the process must
+	   terminate.  */
+L(exitcode):
+	/* This removes the parameters passed to the function given to
+	   'makecontext' from the stack.  EBX contains the number of
+	   parameters (see above).  */
+	leal	(%esp,%ebx,4), %esp
+
+	cmpl	$0, (%esp)		/* Check the next context.  */
+	je	2f			/* If it is zero exit.  */
+
+	call	HIDDEN_JUMPTARGET(__setcontext)
+	/* If this returns (which can happen if the syscall fails) we'll
+	   exit the program with the return error value (-1).  */
+	jmp L(call_exit)
+
+2:
+	/* Exit with status 0.  */
+	xorl	%eax, %eax
+
+L(call_exit):
+	/* Align the stack and pass the exit code (from %eax).  */
+	andl	$0xfffffff0, %esp
+	subl	$12, %esp
+	pushl	%eax
+
+	call	HIDDEN_JUMPTARGET(exit)
+	/* The 'exit' call should never return.  In case it does cause
+	   the process to terminate.  */
+	hlt
+	cfi_startproc
+END(__makecontext)
+
+weak_alias (__makecontext, makecontext)