Implement getcontext, setcontext, makecontext, swapcontext
* common.din (getcontext): Export.
(makecontext): Export.
(setcontext): Export.
(swapcontext): Export.
* exceptions.cc (__unwind_single_frame): New static functions, 64 bit
only.
(setcontext): New function.
(getcontext): New function.
(swapcontext): New function.
(__cont_link_context): New function.
(makecontext): New function.
* include/cygwin/version.h (CYGWIN_VERSION_DLL_MAJOR): Bump to 2002.
(CYGWIN_VERSION_API_MINOR): Bump.
* include/ucontext.h (getcontext): Add prototype.
(setcontext): Ditto.
(swapcontext): Ditto.
(makecontext): Ditto.
* ntdll.h (NtContinue): Ditto.
* new-features.xml (ov-new2.2): Add new section. Document getcontext,
setcontext, makecontext, swapcontext.
* posix.xml (std-deprec): Add getcontext, setcontext, makecontext,
swapcontext.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen
@ -14,6 +14,7 @@ details. */
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#include "miscfuncs.h"
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#include <imagehlp.h>
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#include <stdlib.h>
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#include <stdarg.h>
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#include <syslog.h>
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#include <wchar.h>
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#include <ucontext.h>
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@ -1863,3 +1864,226 @@ _cygtls::signal_debugger (siginfo_t& si)
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ResumeThread (th);
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}
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}
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#ifdef __x86_64__
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static inline void
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__unwind_single_frame (PCONTEXT ctx)
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{
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/* Amazing, but true: On 32 bit, RtlCaptureContext returns the context
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matching the caller of getcontext, so all we have to do is call it.
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On 64 bit, RtlCaptureContext returns the exact context of its own
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caller, so we have to unwind virtually by a single frame to get the
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context of the caller of getcontext. */
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PRUNTIME_FUNCTION f;
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ULONG64 imagebase;
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UNWIND_HISTORY_TABLE hist;
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DWORD64 establisher;
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PVOID hdl;
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f = RtlLookupFunctionEntry (ctx->Rip, &imagebase, &hist);
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if (f)
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RtlVirtualUnwind (0, imagebase, ctx->Rip, f, ctx, &hdl, &establisher,
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NULL);
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else
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{
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ctx->Rip = *(ULONG_PTR *) ctx->Rsp;
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ctx->Rsp += 8;
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}
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}
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#endif
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extern "C" int
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setcontext (const ucontext_t *ucp)
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{
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PCONTEXT ctx = (PCONTEXT) &ucp->uc_mcontext;
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_my_tls.sigmask = ucp->uc_sigmask;
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#ifdef __x86_64__
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/* Apparently a call to NtContinue works on 64 bit as well, but using
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RtlRestoreContext is the blessed way. */
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RtlRestoreContext (ctx, NULL);
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#else
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NtContinue (ctx, FALSE);
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#endif
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/* If we got here, something was wrong. */
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set_errno (EINVAL);
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return -1;
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}
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#ifdef __x86_64__
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extern "C" int
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getcontext (ucontext_t *ucp)
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{
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PCONTEXT ctx = (PCONTEXT) &ucp->uc_mcontext;
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ctx->ContextFlags = CONTEXT_FULL;
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RtlCaptureContext (ctx);
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__unwind_single_frame (ctx);
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/* Successful getcontext is supposed to return 0. If we don't set rax to 0
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here, there's a chance that code like this:
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if (getcontext (&ctx) != 0)
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assumes that getcontext failed after calling setcontext (&ctx).
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Same goes for eax on 32 bit, see assembler implementation below. */
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ucp->uc_mcontext.rax = 0;
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ucp->uc_sigmask = ucp->uc_mcontext.oldmask = _my_tls.sigmask;
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/* Do not touch any other member of ucontext_t. */
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return 0;
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}
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extern "C" int
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swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
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{
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PCONTEXT ctx = (PCONTEXT) &oucp->uc_mcontext;
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ctx->ContextFlags = CONTEXT_FULL;
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RtlCaptureContext (ctx);
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__unwind_single_frame (ctx);
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/* See above. */
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oucp->uc_mcontext.rax = 0;
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oucp->uc_sigmask = oucp->uc_mcontext.oldmask = _my_tls.sigmask;
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return setcontext (ucp);
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}
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/* Trampoline function to set the context to uc_link. The pointer to the
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address of uc_link is stored in the callee-saved register $rbx. If uc_link
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is NULL, call exit. */
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__asm__ (" \n\
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.global __cont_link_context \n\
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__cont_link_context: \n\
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movq %rbx, %rsp \n\
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popq %rcx \n\
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testq %rcx, %rcx \n\
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je 1f \n\
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call setcontext \n\
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movq $0xff, %rcx \n\
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1: \n\
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call cygwin_exit \n\
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nop \n\
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");
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#else
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/* On 32 bit it's crucial to call RtlCaptureContext in a way which makes sure
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the callee-saved registers, especially $ebx, are not changed by the calling
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function. If so, makecontext/__cont_link_context would be broken.
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Both functions are split into the first half in assembler, and the second
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half in C to allow easy access to _my_tls. */
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extern "C" int
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__getcontext (ucontext_t *ucp)
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{
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ucp->uc_mcontext.eax = 0;
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ucp->uc_sigmask = ucp->uc_mcontext.oldmask = _my_tls.sigmask;
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return 0;
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}
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__asm__ (" \n\
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.global _getcontext \n\
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_getcontext: \n\
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pushl %ebp \n\
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movl %esp, %ebp \n\
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movl 8(%esp), %eax \n\
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pushl %eax \n\
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call _RtlCaptureContext@4 \n\
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popl %ebp \n\
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jmp ___getcontext \n\
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nop \n\
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");
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extern "C" int
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__swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
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{
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oucp->uc_mcontext.eax = 0;
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oucp->uc_sigmask = oucp->uc_mcontext.oldmask = _my_tls.sigmask;
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return setcontext (ucp);
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}
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__asm__ (" \n\
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.global _swapcontext \n\
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_swapcontext: \n\
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pushl %ebp \n\
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movl %esp, %ebp \n\
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movl 8(%esp), %eax \n\
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pushl %eax \n\
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call _RtlCaptureContext@4 \n\
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popl %ebp \n\
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jmp ___swapcontext \n\
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nop \n\
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");
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/* Trampoline function to set the context to uc_link. The pointer to the
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address of uc_link is stored in the callee-saved register $ebx. If uc_link
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is NULL, call exit. */
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__asm__ (" \n\
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.global ___cont_link_context \n\
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___cont_link_context: \n\
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movl %ebx, %esp \n\
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movl (%esp), %eax \n\
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testl %eax, %eax \n\
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je 1f \n\
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call _setcontext \n\
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movl $0xff, (%esp) \n\
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1: \n\
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call _cygwin_exit \n\
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nop \n\
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");
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#endif
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/* makecontext is modelled after GLibc's makecontext. The stack from uc_stack
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is prepared so that it starts with a pointer to the linked context uc_link,
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followed by the arguments to func, and finally at the bottom the "return"
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address set to __cont_link_context. In the ucp context, rbx/ebx is set to
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point to the stack address where the pointer to uc_link is stored. The
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requirement to make this work is that rbx/ebx are callee-saved registers
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per the ABI. If any function is called which doesn't follow the ABI
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conventions, e.g. assembler code, this method will break. But that's ok. */
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extern "C" void
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makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
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{
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extern void __cont_link_context (void);
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uintptr_t *sp;
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va_list ap;
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sp = (uintptr_t *) ((uintptr_t) ucp->uc_stack.ss_sp
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+ ucp->uc_stack.ss_size);
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sp -= (argc + 1);
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sp = (uintptr_t *) ((uintptr_t) sp & ~0xf);
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--sp;
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sp[0] = (uintptr_t) __cont_link_context;
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sp[argc + 1] = (uintptr_t) ucp->uc_link;
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#ifdef __x86_64__
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ucp->uc_mcontext.rip = (uint64_t) func;
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ucp->uc_mcontext.rbx = (uint64_t) (sp + argc + 1);
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ucp->uc_mcontext.rsp = (uint64_t) sp;
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#else
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ucp->uc_mcontext.eip = (uint32_t) func;
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ucp->uc_mcontext.ebx = (uint32_t) (sp + argc + 1);
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ucp->uc_mcontext.esp = (uint32_t) sp;
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#endif
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va_start (ap, argc);
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for (int i = 0; i < argc; ++i)
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#ifdef __x86_64__
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switch (i)
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{
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case 0:
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ucp->uc_mcontext.rcx = va_arg (ap, uintptr_t);
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break;
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case 1:
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ucp->uc_mcontext.rdx = va_arg (ap, uintptr_t);
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break;
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case 2:
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ucp->uc_mcontext.r8 = va_arg (ap, uintptr_t);
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break;
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case 3:
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ucp->uc_mcontext.r9 = va_arg (ap, uintptr_t);
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break;
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default:
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sp[i + 1] = va_arg (ap, uintptr_t);
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break;
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}
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#else
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sp[i + 1] = va_arg (ap, uintptr_t);
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#endif
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va_end (ap);
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}
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