win: Add and use a custom CaptureContext() implementation

util/win/capture_context.asm

+; Copyright 2015 The Crashpad Authors. All rights reserved.
+;
+; Licensed under the Apache License, Version 2.0 (the "License");
+; you may not use this file except in compliance with the License.
+; You may obtain a copy of the License at
+;
+;     http://www.apache.org/licenses/LICENSE-2.0
+;
+; Unless required by applicable law or agreed to in writing, software
+; distributed under the License is distributed on an "AS IS" BASIS,
+; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+; See the License for the specific language governing permissions and
+; limitations under the License.
+
+; Detect ml64 assembling for x86_64 by checking for rax.
+ifdef rax
+_M_X64 equ 1
+else
+_M_IX86 equ 1
+endif
+
+ifdef _M_IX86
+.586
+.XMM
+.model flat
+endif
+
+offsetof macro structure, field
+  exitm <structure.&field>
+endm
+
+; The CONTEXT structure definitions that follow are based on those in <winnt.h>.
+; Field names are prefixed (as in c_Rax) to avoid colliding with the predefined
+; register names (such as Rax).
+
+ifdef _M_IX86
+
+CONTEXT_i386 equ 10000h
+CONTEXT_CONTROL equ CONTEXT_i386 or 1h
+CONTEXT_INTEGER equ CONTEXT_i386 or 2h
+CONTEXT_SEGMENTS equ CONTEXT_i386 or 4h
+CONTEXT_FLOATING_POINT equ CONTEXT_i386 or 8h
+CONTEXT_DEBUG_REGISTERS equ CONTEXT_i386 or 10h
+CONTEXT_EXTENDED_REGISTERS equ CONTEXT_i386 or 20h
+CONTEXT_XSTATE equ CONTEXT_i386 or 40h
+
+MAXIMUM_SUPPORTED_EXTENSION equ 512
+
+CONTEXT struct
+  c_ContextFlags dword ?
+
+  c_Dr0 dword ?
+  c_Dr1 dword ?
+  c_Dr2 dword ?
+  c_Dr3 dword ?
+  c_Dr6 dword ?
+  c_Dr7 dword ?
+
+  struct c_FloatSave
+    f_ControlWord dword ?
+    f_StatusWord dword ?
+    f_TagWord dword ?
+    f_ErrorOffset dword ?
+    f_ErrorSelector dword ?
+    f_DataOffset dword ?
+    f_DataSelector dword ?
+    f_RegisterArea byte 80 dup(?)
+
+    union
+      f_Spare0 dword ?  ; As in FLOATING_SAVE_AREA.
+      f_Cr0NpxState dword ?  ; As in WOW64_FLOATING_SAVE_AREA.
+    ends
+  ends
+
+  c_SegGs dword ?
+  c_SegFs dword ?
+  c_SegEs dword ?
+  c_SegDs dword ?
+
+  c_Edi dword ?
+  c_Esi dword ?
+  c_Ebx dword ?
+  c_Edx dword ?
+  c_Ecx dword ?
+  c_Eax dword ?
+
+  c_Ebp dword ?
+
+  c_Eip dword ?
+  c_SegCs dword ?
+
+  c_EFlags dword ?
+
+  c_Esp dword ?
+  c_SegSs dword ?
+
+  c_ExtendedRegisters byte MAXIMUM_SUPPORTED_EXTENSION dup(?)
+CONTEXT ends
+
+elseifdef _M_X64
+
+M128A struct 16
+  m_Low qword ?
+  m_High qword ?
+M128A ends
+
+CONTEXT_AMD64 equ 100000h
+CONTEXT_CONTROL equ CONTEXT_AMD64 or 1h
+CONTEXT_INTEGER equ CONTEXT_AMD64 or 2h
+CONTEXT_SEGMENTS equ CONTEXT_AMD64 or 4h
+CONTEXT_FLOATING_POINT equ CONTEXT_AMD64 or 8h
+CONTEXT_DEBUG_REGISTERS equ CONTEXT_AMD64 or 10h
+CONTEXT_XSTATE equ CONTEXT_AMD64 or 40h
+
+CONTEXT struct 16
+  c_P1Home qword ?
+  c_P2Home qword ?
+  c_P3Home qword ?
+  c_P4Home qword ?
+  c_P5Home qword ?
+  c_P6Home qword ?
+
+  c_ContextFlags dword ?
+  c_MxCsr dword ?
+
+  c_SegCs word ?
+  c_SegDs word ?
+  c_SegEs word ?
+  c_SegFs word ?
+  c_SegGs word ?
+  c_SegSs word ?
+
+  c_EFlags dword ?
+
+  c_Dr0 qword ?
+  c_Dr1 qword ?
+  c_Dr2 qword ?
+  c_Dr3 qword ?
+  c_Dr6 qword ?
+  c_Dr7 qword ?
+
+  c_Rax qword ?
+  c_Rcx qword ?
+  c_Rdx qword ?
+  c_Rbx qword ?
+  c_Rsp qword ?
+  c_Rbp qword ?
+  c_Rsi qword ?
+  c_Rdi qword ?
+  c_R8 qword ?
+  c_R9 qword ?
+  c_R10 qword ?
+  c_R11 qword ?
+  c_R12 qword ?
+  c_R13 qword ?
+  c_R14 qword ?
+  c_R15 qword ?
+
+  c_Rip qword ?
+
+  union
+    struct c_FltSave
+      f_ControlWord word ?
+      f_StatusWord word ?
+      f_TagWord byte ?
+      f_Reserved1 byte ?
+      f_ErrorOpcode word ?
+      f_ErrorOffset dword ?
+      f_ErrorSelector word ?
+      f_Reserved2 word ?
+      f_DataOffset dword ?
+      f_DataSelector word ?
+      f_Reserved3 word ?
+      f_MxCsr dword ?
+      f_MxCsr_Mask dword ?
+      f_FloatRegisters M128A 8 dup(<?>)
+      f_XmmRegisters M128A 16 dup(<?>)
+      f_Reserved4 byte 96 dup(?)
+    ends
+    struct
+      fx_Header M128A 2 dup(<?>)
+      fx_Legacy M128A 8 dup(<?>)
+      fx_Xmm0 M128A <?>
+      fx_Xmm1 M128A <?>
+      fx_Xmm2 M128A <?>
+      fx_Xmm3 M128A <?>
+      fx_Xmm4 M128A <?>
+      fx_Xmm5 M128A <?>
+      fx_Xmm6 M128A <?>
+      fx_Xmm7 M128A <?>
+      fx_Xmm8 M128A <?>
+      fx_Xmm9 M128A <?>
+      fx_Xmm10 M128A <?>
+      fx_Xmm11 M128A <?>
+      fx_Xmm12 M128A <?>
+      fx_Xmm13 M128A <?>
+      fx_Xmm14 M128A <?>
+      fx_Xmm15 M128A <?>
+    ends
+  ends
+
+  c_VectorRegister M128A 26 dup(<?>)
+  c_VectorControl qword ?
+
+  c_DebugControl qword ?
+  c_LastBranchToRip qword ?
+  c_LastBranchFromRip qword ?
+  c_LastExceptionToRip qword ?
+  c_LastExceptionFromRip qword ?
+CONTEXT ends
+
+endif
+
+; namespace crashpad {
+; void CaptureContext(CONTEXT* context)
+; }  // namespace crashpad
+ifdef _M_IX86
+CAPTURECONTEXT_SYMBOL equ ?CaptureContext@crashpad@@YAXPAU_CONTEXT@@@Z
+elseifdef _M_X64
+CAPTURECONTEXT_SYMBOL equ ?CaptureContext@crashpad@@YAXPEAU_CONTEXT@@@Z
+endif
+
+_TEXT segment
+public CAPTURECONTEXT_SYMBOL
+
+ifdef _M_IX86
+
+CAPTURECONTEXT_SYMBOL proc
+
+  push ebp
+  mov ebp, esp
+
+  ; pushfd first, because some instructions affect eflags. eflags will be in
+  ; [ebp-4].
+  pushfd
+
+  ; Save the original value of ebx, and use ebx to hold the CONTEXT* argument.
+  ; The original value of ebx will be in [ebp-8].
+  push ebx
+  mov ebx, [ebp+8]
+
+  ; General-purpose registers whose values haven’t changed can be captured
+  ; directly.
+  mov [ebx.CONTEXT].c_Edi, edi
+  mov [ebx.CONTEXT].c_Esi, esi
+  mov [ebx.CONTEXT].c_Edx, edx
+  mov [ebx.CONTEXT].c_Ecx, ecx
+  mov [ebx.CONTEXT].c_Eax, eax
+
+  ; Now that the original value of edx has been saved, it can be repurposed to
+  ; hold other registers’ values.
+
+  ; The original ebx was saved on the stack above.
+  mov edx, dword ptr [ebp-8]
+  mov [ebx.CONTEXT].c_Ebx, edx
+
+  ; The original ebp was saved on the stack in this function’s prologue.
+  mov edx, dword ptr [ebp]
+  mov [ebx.CONTEXT].c_Ebp, edx
+
+  ; eip can’t be accessed directly, but the return address saved on the stack
+  ; by the call instruction that reached this function can be used.
+  mov edx, dword ptr [ebp+4]
+  mov [ebx.CONTEXT].c_Eip, edx
+
+  ; The original eflags was saved on the stack above.
+  mov edx, dword ptr [ebp-4]
+  mov [ebx.CONTEXT].c_EFlags, edx
+
+  ; esp was saved in ebp in this function’s prologue, but the caller’s esp is 8
+  ; more than this value: 4 for the original ebp saved on the stack in this
+  ; function’s prologue, and 4 for the return address saved on the stack by the
+  ; call instruction that reached this function.
+  lea edx, [ebp+8]
+  mov [ebx.CONTEXT].c_Esp, edx
+
+  ; The segment registers are 16 bits wide, but CONTEXT declares them as
+  ; unsigned 32-bit values, so zero the top half.
+  xor edx, edx
+  mov dx, gs
+  mov [ebx.CONTEXT].c_SegGs, edx
+  mov dx, fs
+  mov [ebx.CONTEXT].c_SegFs, edx
+  mov dx, es
+  mov [ebx.CONTEXT].c_SegEs, edx
+  mov dx, ds
+  mov [ebx.CONTEXT].c_SegDs, edx
+  mov dx, cs
+  mov [ebx.CONTEXT].c_SegCs, edx
+  mov dx, ss
+  mov [ebx.CONTEXT].c_SegSs, edx
+
+  ; Prepare for the string move that will populate the ExtendedRegisters area,
+  ; or the string store that will zero it.
+  cld
+
+  ; Use cpuid 1 to check whether fxsave is supported. If it is, perform it
+  ; before fnsave because fxsave is a less-destructive operation.
+  mov esi, ebx
+  mov eax, 1
+  cpuid
+  mov ebx, esi
+
+  test edx, 01000000  ; FXSR
+  jnz $FXSave
+
+  ; fxsave is not supported. Set ContextFlags to not include
+  ; CONTEXT_EXTENDED_REGISTERS, and zero the ExtendedRegisters area.
+  mov [ebx.CONTEXT].c_ContextFlags, CONTEXT_i386 or \
+                                    CONTEXT_CONTROL or \
+                                    CONTEXT_INTEGER or \
+                                    CONTEXT_SEGMENTS or \
+                                    CONTEXT_FLOATING_POINT
+  lea edi, [ebx.CONTEXT].c_ExtendedRegisters
+  xor eax, eax
+  mov ecx, MAXIMUM_SUPPORTED_EXTENSION / sizeof(dword)  ; 128
+  rep stosd
+  jmp $FXSaveDone
+
+$FXSave:
+  ; fxsave is supported. Set ContextFlags to include CONTEXT_EXTENDED_REGISTERS.
+  mov [ebx.CONTEXT].c_ContextFlags, CONTEXT_i386 or \
+                                    CONTEXT_CONTROL or \
+                                    CONTEXT_INTEGER or \
+                                    CONTEXT_SEGMENTS or \
+                                    CONTEXT_FLOATING_POINT or \
+                                    CONTEXT_EXTENDED_REGISTERS
+
+  ; fxsave requires a 16 byte-aligned destination memory area. Nothing
+  ; guarantees the alignment of a CONTEXT structure, so create a temporary
+  ; aligned fxsave destination on the stack.
+  and esp, 0fffffff0h
+  sub esp, MAXIMUM_SUPPORTED_EXTENSION
+
+  ; Zero out the temporary fxsave area before performing the fxsave. Some of the
+  ; fxsave area may not be written by fxsave, and some is definitely not written
+  ; by fxsave.
+  mov edi, esp
+  xor eax, eax
+  mov ecx, MAXIMUM_SUPPORTED_EXTENSION / sizeof(dword)  ; 128
+  rep stosd
+
+  fxsave [esp]
+
+  ; Copy the temporary fxsave area into the CONTEXT structure.
+  lea edi, [ebx.CONTEXT].c_ExtendedRegisters
+  mov esi, esp
+  mov ecx, MAXIMUM_SUPPORTED_EXTENSION / sizeof(dword)  ; 128
+  rep movsd
+
+  ; Free the stack space used for the temporary fxsave area.
+  lea esp, [ebp-8]
+
+  ; TODO(mark): AVX/xsave support.
+  ; https://code.google.com/p/crashpad/issues/detail?id=58
+
+$FXSaveDone:
+  ; fnsave reinitializes the FPU with an implicit finit operation, so use frstor
+  ; to restore the original state.
+  fnsave [ebx.Context].c_FloatSave

[scottmg, 2015/09/30 17:33:38]

Context -> CONTEXT for consistency (and the next 2)

+  frstor [ebx.Context].c_FloatSave
+
+  ; cr0 is inaccessible from user code, and this field would not be used anyway.
+  mov [ebx.Context].c_FloatSave.f_Cr0NpxState, 0
+
+  ; The debug registers can’t be read from user code, so zero them out in the
+  ; CONTEXT structure. context->ContextFlags doesn’t indicate that they are
+  ; present.
+  mov [ebx.CONTEXT].c_Dr0, 0
+  mov [ebx.CONTEXT].c_Dr1, 0
+  mov [ebx.CONTEXT].c_Dr2, 0
+  mov [ebx.CONTEXT].c_Dr3, 0
+  mov [ebx.CONTEXT].c_Dr6, 0
+  mov [ebx.CONTEXT].c_Dr7, 0
+
+  ; Clean up by restoring clobbered registers, even those considered volatile
+  ; by the ABI, so that the captured context represents the state at this
+  ; function’s exit.
+  mov edi, [ebx.CONTEXT].c_Edi
+  mov esi, [ebx.CONTEXT].c_Esi
+  mov edx, [ebx.CONTEXT].c_Edx
+  mov ecx, [ebx.CONTEXT].c_Ecx
+  mov eax, [ebx.CONTEXT].c_Eax
+  pop ebx
+  popfd
+
+  pop ebp
+
+  ret
+
+CAPTURECONTEXT_SYMBOL endp
+
+elseifdef _M_X64
+
+CAPTURECONTEXT_SYMBOL proc frame
+
+  push rbp
+  .pushreg rbp
+  mov rbp, rsp
+  .setframe rbp, 0
+
+  ; Note that 16-byte stack alignment is not maintained because this function
+  ; does not call out to any other.
+
+  ; pushfq first, because some instructions affect rflags. rflags will be in
+  ; [rbp-8].
+  pushfq
+  .allocstack 8
+  .endprolog
+
+  mov [rcx.CONTEXT].c_ContextFlags, CONTEXT_AMD64 or \
+                                    CONTEXT_CONTROL or \
+                                    CONTEXT_INTEGER or \
+                                    CONTEXT_SEGMENTS or \
+                                    CONTEXT_FLOATING_POINT
+
+  ; General-purpose registers whose values haven’t changed can be captured
+  ; directly.
+  mov [rcx.CONTEXT].c_Rax, rax
+  mov [rcx.CONTEXT].c_Rdx, rdx
+  mov [rcx.CONTEXT].c_Rbx, rbx
+  mov [rcx.CONTEXT].c_Rsi, rsi
+  mov [rcx.CONTEXT].c_Rdi, rdi
+  mov [rcx.CONTEXT].c_R8, r8
+  mov [rcx.CONTEXT].c_R9, r9
+  mov [rcx.CONTEXT].c_R10, r10
+  mov [rcx.CONTEXT].c_R11, r11
+  mov [rcx.CONTEXT].c_R12, r12
+  mov [rcx.CONTEXT].c_R13, r13
+  mov [rcx.CONTEXT].c_R14, r14
+  mov [rcx.CONTEXT].c_R15, r15
+
+  ; Because of the calling convention, there’s no way to recover the value of
+  ; the caller’s rcx as it existed prior to calling this function. This
+  ; function captures a snapshot of the register state at its return, which
+  ; involves rcx containing a pointer to its first argument.
+  mov [rcx.CONTEXT].c_Rcx, rcx
+
+  ; Now that the original value of rax has been saved, it can be repurposed to
+  ; hold other registers’ values.
+
+  ; Save mxcsr. This is duplicated in context->FltSave.MxCsr, saved by fxsave
+  ; below.
+  stmxcsr [rcx.CONTEXT].c_MxCsr
+
+  ; Segment registers.
+  mov [rcx.CONTEXT].c_SegCs, cs
+  mov [rcx.CONTEXT].c_SegDs, ds
+  mov [rcx.CONTEXT].c_SegEs, es
+  mov [rcx.CONTEXT].c_SegFs, fs
+  mov [rcx.CONTEXT].c_SegGs, gs
+  mov [rcx.CONTEXT].c_SegSs, ss
+
+  ; The original rflags was saved on the stack above. Note that the CONTEXT
+  ; structure only stores eflags, the low 32 bits. The high 32 bits in rflags
+  ; are reserved.
+  mov rax, qword ptr [rbp-8]
+  mov [rcx.CONTEXT].c_EFlags, eax
+
+  ; rsp was saved in rbp in this function’s prologue, but the caller’s rsp is
+  ; 16 more than this value: 8 for the original rbp saved on the stack in this
+  ; function’s prologue, and 8 for the return address saved on the stack by the
+  ; call instruction that reached this function.
+  lea rax, [rbp+16]
+  mov [rcx.CONTEXT].c_Rsp, rax
+
+  ; The original rbp was saved on the stack in this function’s prologue.
+  mov rax, qword ptr [rbp]
+  mov [rcx.CONTEXT].c_Rbp, rax
+
+  ; rip can’t be accessed directly, but the return address saved on the stack by
+  ; the call instruction that reached this function can be used.
+  mov rax, qword ptr [rbp+8]
+  mov [rcx.CONTEXT].c_Rip, rax
+
+  ; Zero out the fxsave area before performing the fxsave. Some of the fxsave
+  ; area may not be written by fxsave, and some is definitely not written by
+  ; fxsave. Also, zero out the unused VectorRegister and VectorControl fields,
+  ; and the debug control register fields.

[scottmg, 2015/09/30 17:33:38]

Maybe something about "the rest of the structure" to correspond to the code.

+  mov rbx, rcx
+  cld
+  lea rdi, [rcx.CONTEXT].c_FltSave
+  xor rax, rax
+  mov rcx, (sizeof(CONTEXT) - offsetof(CONTEXT, c_FltSave)) / \
+           sizeof(qword)  ; 122
+  rep stosq
+  mov rcx, rbx
+
+  ; Save the floating point (including SSE) state. The CONTEXT structure is
+  ; declared as 16-byte-aligned, which is correct for this operation.
+  fxsave [rcx.CONTEXT].c_FltSave
+
+  ; TODO(mark): AVX/xsave support.
+  ; https://code.google.com/p/crashpad/issues/detail?id=58
+
+  ; The register parameter home address fields aren’t used, so zero them out.
+  mov [rcx.CONTEXT].c_P1Home, 0
+  mov [rcx.CONTEXT].c_P2Home, 0
+  mov [rcx.CONTEXT].c_P3Home, 0
+  mov [rcx.CONTEXT].c_P4Home, 0
+  mov [rcx.CONTEXT].c_P5Home, 0
+  mov [rcx.CONTEXT].c_P6Home, 0
+
+  ; The debug registers can’t be read from user code, so zero them out in the
+  ; CONTEXT structure. context->ContextFlags doesn’t indicate that they are
+  ; present.
+  mov [rcx.CONTEXT].c_Dr0, 0
+  mov [rcx.CONTEXT].c_Dr1, 0
+  mov [rcx.CONTEXT].c_Dr2, 0
+  mov [rcx.CONTEXT].c_Dr3, 0
+  mov [rcx.CONTEXT].c_Dr6, 0
+  mov [rcx.CONTEXT].c_Dr7, 0
+
+  ; Clean up by restoring clobbered registers, even those considered volatile by
+  ; the ABI, so that the captured context represents the state at this
+  ; function’s exit.
+  mov rax, [rcx.CONTEXT].c_Rax
+  mov rbx, [rcx.CONTEXT].c_Rbx
+  mov rdi, [rcx.CONTEXT].c_Rdi
+  popfq
+
+  pop rbp
+
+  ret
+
+CAPTURECONTEXT_SYMBOL endp
+
+endif
+
+_TEXT ends
+end