b4eb6c7533
use set_mcontext() to restore the context in sigreturn(). Since we put the syscall number and the syscall arguments in the trapframe (we don't save the scratch registers for syscalls, which allows us to reuse the space to our advantage), create a MD specific flag so that we save the scratch registers even for syscalls. We would not be able to restart a syscall otherwise. The signal trampoline does not need to flush the regiters anymore, because get_mcontext() already handles that. In fact, if we set up the context correctly, we do not need to have a trampoline at all. This change however only minimally changes the trampoline code. In follow-up commits this can be further optimized. Note that normally we preserve cfm and iip in the trapframe created by the EPC syscall path when we restore a context in set_mcontext() because those fields are not normally set for a synchronuous context. The kernel puts the return address and frame info of the syscall stub in there. By preserving these fields we hide this detail from userland which allows us to use setcontext(2) for user created contexts. However, sigreturn() is commonly called from the trampoline, which means that if we preserve cfm and iip in all cases, we would return to the trampoline after the sigreturn(), which means we hit the safety net: we call exit(2). So, we do not preserve cfm and iip when we have a synchronous context that also has scratch registers (the uncommon context created by sendsig() only), under the assumption that if such a context is created in userland, something special is going on and the use of cfm and iip is then just another quirk. All this is invisible in the common case.
105 lines
4.6 KiB
C
105 lines
4.6 KiB
C
/*-
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* Copyright (c) 1999, 2003 Marcel Moolenaar
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer
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* in this position and unchanged.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#ifndef _MACHINE_UCONTEXT_H_
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#define _MACHINE_UCONTEXT_H_
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#include <machine/_regset.h>
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/*
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* The mc_flags field provides the necessary clues when dealing with the gory
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* details of ia64 specific contexts. A comprehensive explanation is added for
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* everybody's sanity, including the author's.
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*
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* The first and foremost variation in the context is synchronous contexts
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* (= synctx) versus asynchronous contexts (= asynctx). A synctx is created
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* synchronously WRT program execution and has the advantage that none of the
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* scratch registers have to be saved. They are assumed to be clobbered by the
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* call to the function that creates the context. An asynctx needs to have the
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* scratch registers preserved because it can describe any point in a thread's
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* (or process') execution.
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*
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* Below a description of the flags and their meaning:
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*
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* _MC_FLAGS_ASYNC_CONTEXT
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* If set, indicates that mc_scratch and mc_scratch_fp are both
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* valid. IFF not set, _MC_FLAGS_RETURN_VALID indicates if the
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* return registers are valid or not.
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* _MC_FLAGS_HIGHFP_VALID
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* If set, indicates that the high FP registers (f32-f127) are
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* valid. This flag is very likely not going to be set for any
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* sensible synctx, but is not explicitly disallowed. Any synctx
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* that has this flag may or may not have the high FP registers
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* restored. In short: don't do it.
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* _MC_FLAGS_KSE_SET_MBOX
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* This flag is special to setcontext(2) and swapcontext(2). It
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* instructs the kernel to write the value in mc_special.isr to
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* the memory address pointed to by mc_special.ifa. This allows
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* the kernel to switch to a new context in a KSE based threaded
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* program. Note that this is a non-srandard extension to the
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* otherwise standard system calls and use of this flag should be
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* limited to KSE.
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* _MC_FLAGS_RETURN_VALID
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* If set and _MC_FLAGS_ASYNC_CONTEXT is not set indicates that
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* the ABI defined return registers are valid. Both getcontext(2)
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* and swapcontext(2) need to save the system call return values.
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* Any synctx that does not have this flag may still have the
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* return registers restored from the context.
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* _MC_FLAGS_SCRATCH_VALID
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* If set and _MC_FLAGS_ASYNC_CONTEXT is not set indicates that
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* the scratch registers, but not the FP registers are valid.
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* This flag is set in contexts passed to signal handlers. This
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* flag is a superset of _MC_FLAGS_RETURN_VALID. If both flags
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* are set, this flag takes precedence.
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*/
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typedef struct __mcontext {
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unsigned long mc_flags;
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#define _MC_FLAGS_ASYNC_CONTEXT 0x0001
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#define _MC_FLAGS_HIGHFP_VALID 0x0002
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#define _MC_FLAGS_KSE_SET_MBOX 0x0004
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#define _MC_FLAGS_RETURN_VALID 0x0008
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#define _MC_FLAGS_SCRATCH_VALID 0x0010
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unsigned long _reserved_;
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struct _special mc_special;
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struct _callee_saved mc_preserved;
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struct _callee_saved_fp mc_preserved_fp;
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struct _caller_saved mc_scratch;
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struct _caller_saved_fp mc_scratch_fp;
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struct _high_fp mc_high_fp;
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} mcontext_t;
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#ifdef _KERNEL
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/* Flags for get_mcontext(). See also <sys/ucontext.h>. */
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#define GET_MC_IA64_SCRATCH 0x10
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#endif
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#endif /* !_MACHINE_UCONTEXT_H_ */
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