Update copyright year
[openssl.git] / crypto / perlasm / x86_64-xlate.pl
index 4298b3f418c89227ded643202d694be23c8deff9..29a0eacfd532a6a41db6e986e144b33471920990 100755 (executable)
@@ -1,5 +1,5 @@
 #! /usr/bin/env perl
-# Copyright 2005-2016 The OpenSSL Project Authors. All Rights Reserved.
+# Copyright 2005-2019 The OpenSSL Project Authors. All Rights Reserved.
 #
 # Licensed under the OpenSSL license (the "License").  You may not use
 # this file except in compliance with the License.  You can obtain a copy
 # 7. Stick to explicit ip-relative addressing. If you have to use
 #    GOTPCREL addressing, stick to mov symbol@GOTPCREL(%rip),%r??.
 #    Both are recognized and translated to proper Win64 addressing
-#    modes. To support legacy code a synthetic directive, .picmeup,
-#    is implemented. It puts address of the *next* instruction into
-#    target register, e.g.:
-#
-#              .picmeup        %rax
-#              lea             .Label-.(%rax),%rax
+#    modes.
 #
 # 8. In order to provide for structured exception handling unified
 #    Win64 prologue copies %rsp value to %rax. For further details
@@ -100,7 +95,7 @@ elsif (!$gas)
     {  $nasm = $1 + $2*0.01; $PTR="";  }
     elsif (`ml64 2>&1` =~ m/Version ([0-9]+)\.([0-9]+)(\.([0-9]+))?/)
     {  $masm = $1 + $2*2**-16 + $4*2**-32;   }
-    die "no assembler found on %PATH" if (!($nasm || $masm));
+    die "no assembler found on %PATH%" if (!($nasm || $masm));
     $win64=1;
     $elf=0;
     $decor="\$L\$";
@@ -130,7 +125,7 @@ my %globals;
                $self->{sz} = "";
            } elsif ($self->{op} =~ /^p/ && $' !~ /^(ush|op|insrw)/) { # SSEn
                $self->{sz} = "";
-           } elsif ($self->{op} =~ /^v/) { # VEX
+           } elsif ($self->{op} =~ /^[vk]/) { # VEX or k* such as kmov
                $self->{sz} = "";
            } elsif ($self->{op} =~ /mov[dq]/ && $$line =~ /%xmm/) {
                $self->{sz} = "";
@@ -217,24 +212,33 @@ my %globals;
            }
            sprintf "\$%s",$self->{value};
        } else {
-           $self->{value} =~ s/0x([0-9a-f]+)/0$1h/ig if ($masm);
-           sprintf "%s",$self->{value};
+           my $value = $self->{value};
+           $value =~ s/0x([0-9a-f]+)/0$1h/ig if ($masm);
+           sprintf "%s",$value;
        }
     }
 }
 { package ea;          # pick up effective addresses: expr(%reg,%reg,scale)
+
+    my %szmap = (      b=>"BYTE$PTR",    w=>"WORD$PTR",
+                       l=>"DWORD$PTR",   d=>"DWORD$PTR",
+                       q=>"QWORD$PTR",   o=>"OWORD$PTR",
+                       x=>"XMMWORD$PTR", y=>"YMMWORD$PTR",
+                       z=>"ZMMWORD$PTR" ) if (!$gas);
+
     sub re {
        my      ($class, $line, $opcode) = @_;
        my      $self = {};
        my      $ret;
 
        # optional * ----vvv--- appears in indirect jmp/call
-       if ($$line =~ /^(\*?)([^\(,]*)\(([%\w,]+)\)/) {
+       if ($$line =~ /^(\*?)([^\(,]*)\(([%\w,]+)\)((?:{[^}]+})*)/) {
            bless $self, $class;
            $self->{asterisk} = $1;
            $self->{label} = $2;
            ($self->{base},$self->{index},$self->{scale})=split(/,/,$3);
            $self->{scale} = 1 if (!defined($self->{scale}));
+           $self->{opmask} = $4;
            $ret = $self;
            $$line = substr($$line,@+[0]); $$line =~ s/^\s+//;
 
@@ -275,6 +279,8 @@ my %globals;
            $self->{label} =~ s/\b([0-9]+)\b/$1>>0/eg;
        }
 
+       # if base register is %rbp or %r13, see if it's possible to
+       # flip base and index registers [for better performance]
        if (!$self->{label} && $self->{index} && $self->{scale}==1 &&
            $self->{base} =~ /(rbp|r13)/) {
                $self->{base} = $self->{index}; $self->{index} = $1;
@@ -284,19 +290,16 @@ my %globals;
            $self->{label} =~ s/^___imp_/__imp__/   if ($flavour eq "mingw64");
 
            if (defined($self->{index})) {
-               sprintf "%s%s(%s,%%%s,%d)",$self->{asterisk},
-                                       $self->{label},
+               sprintf "%s%s(%s,%%%s,%d)%s",
+                                       $self->{asterisk},$self->{label},
                                        $self->{base}?"%$self->{base}":"",
-                                       $self->{index},$self->{scale};
+                                       $self->{index},$self->{scale},
+                                       $self->{opmask};
            } else {
-               sprintf "%s%s(%%%s)",   $self->{asterisk},$self->{label},$self->{base};
+               sprintf "%s%s(%%%s)%s", $self->{asterisk},$self->{label},
+                                       $self->{base},$self->{opmask};
            }
        } else {
-           my %szmap = (       b=>"BYTE$PTR",  w=>"WORD$PTR",
-                       l=>"DWORD$PTR", d=>"DWORD$PTR",
-                       q=>"QWORD$PTR", o=>"OWORD$PTR",
-                       x=>"XMMWORD$PTR", y=>"YMMWORD$PTR", z=>"ZMMWORD$PTR" );
-
            $self->{label} =~ s/\./\$/g;
            $self->{label} =~ s/(?<![\w\$\.])0x([0-9a-f]+)/0$1h/ig;
            $self->{label} = "($self->{label})" if ($self->{label} =~ /[\*\+\-\/]/);
@@ -308,17 +311,20 @@ my %globals;
            ($mnemonic =~ /^vpbroadcast([qdwb])$/)      && ($sz=$1)  ||
            ($mnemonic =~ /^v(?!perm)[a-z]+[fi]128$/)   && ($sz="x");
 
+           $self->{opmask}  =~ s/%(k[0-7])/$1/;
+
            if (defined($self->{index})) {
-               sprintf "%s[%s%s*%d%s]",$szmap{$sz},
+               sprintf "%s[%s%s*%d%s]%s",$szmap{$sz},
                                        $self->{label}?"$self->{label}+":"",
                                        $self->{index},$self->{scale},
-                                       $self->{base}?"+$self->{base}":"";
+                                       $self->{base}?"+$self->{base}":"",
+                                       $self->{opmask};
            } elsif ($self->{base} eq "rip") {
                sprintf "%s[%s]",$szmap{$sz},$self->{label};
            } else {
-               sprintf "%s[%s%s]",$szmap{$sz},
+               sprintf "%s[%s%s]%s",   $szmap{$sz},
                                        $self->{label}?"$self->{label}+":"",
-                                       $self->{base};
+                                       $self->{base},$self->{opmask};
            }
        }
     }
@@ -330,10 +336,11 @@ my %globals;
        my      $ret;
 
        # optional * ----vvv--- appears in indirect jmp/call
-       if ($$line =~ /^(\*?)%(\w+)/) {
+       if ($$line =~ /^(\*?)%(\w+)((?:{[^}]+})*)/) {
            bless $self,$class;
            $self->{asterisk} = $1;
            $self->{value} = $2;
+           $self->{opmask} = $3;
            $opcode->size($self->size());
            $ret = $self;
            $$line = substr($$line,@+[0]); $$line =~ s/^\s+//;
@@ -357,8 +364,11 @@ my %globals;
     }
     sub out {
        my $self = shift;
-       if ($gas)       { sprintf "%s%%%s",$self->{asterisk},$self->{value}; }
-       else            { $self->{value}; }
+       if ($gas)       { sprintf "%s%%%s%s",   $self->{asterisk},
+                                               $self->{value},
+                                               $self->{opmask}; }
+       else            { $self->{opmask} =~ s/%(k[0-7])/$1/;
+                         $self->{value}.$self->{opmask}; }
     }
 }
 { package label;       # pick up labels, which end with :
@@ -382,9 +392,8 @@ my %globals;
 
        if ($gas) {
            my $func = ($globals{$self->{value}} or $self->{value}) . ":";
-           if ($win64  &&
-                       $current_function->{name} eq $self->{value} &&
-                       $current_function->{abi} eq "svr4") {
+           if ($win64  && $current_function->{name} eq $self->{value}
+                       && $current_function->{abi} eq "svr4") {
                $func .= "\n";
                $func .= "      movq    %rdi,8(%rsp)\n";
                $func .= "      movq    %rsi,16(%rsp)\n";
@@ -429,7 +438,7 @@ my %globals;
        }
     }
 }
-{ package expr;                # pick up expressioins
+{ package expr;                # pick up expressions
     sub re {
        my      ($class, $line, $opcode) = @_;
        my      $self = {};
@@ -457,21 +466,266 @@ my %globals;
        }
     }
 }
+{ package cfi_directive;
+    # CFI directives annotate instructions that are significant for
+    # stack unwinding procedure compliant with DWARF specification,
+    # see http://dwarfstd.org/. Besides naturally expected for this
+    # script platform-specific filtering function, this module adds
+    # three auxiliary synthetic directives not recognized by [GNU]
+    # assembler:
+    #
+    # - .cfi_push to annotate push instructions in prologue, which
+    #   translates to .cfi_adjust_cfa_offset (if needed) and
+    #   .cfi_offset;
+    # - .cfi_pop to annotate pop instructions in epilogue, which
+    #   translates to .cfi_adjust_cfa_offset (if needed) and
+    #   .cfi_restore;
+    # - [and most notably] .cfi_cfa_expression which encodes
+    #   DW_CFA_def_cfa_expression and passes it to .cfi_escape as
+    #   byte vector;
+    #
+    # CFA expressions were introduced in DWARF specification version
+    # 3 and describe how to deduce CFA, Canonical Frame Address. This
+    # becomes handy if your stack frame is variable and you can't
+    # spare register for [previous] frame pointer. Suggested directive
+    # syntax is made-up mix of DWARF operator suffixes [subset of]
+    # and references to registers with optional bias. Following example
+    # describes offloaded *original* stack pointer at specific offset
+    # from *current* stack pointer:
+    #
+    #   .cfi_cfa_expression     %rsp+40,deref,+8
+    #
+    # Final +8 has everything to do with the fact that CFA is defined
+    # as reference to top of caller's stack, and on x86_64 call to
+    # subroutine pushes 8-byte return address. In other words original
+    # stack pointer upon entry to a subroutine is 8 bytes off from CFA.
+
+    # Below constants are taken from "DWARF Expressions" section of the
+    # DWARF specification, section is numbered 7.7 in versions 3 and 4.
+    my %DW_OP_simple = (       # no-arg operators, mapped directly
+       deref   => 0x06,        dup     => 0x12,
+       drop    => 0x13,        over    => 0x14,
+       pick    => 0x15,        swap    => 0x16,
+       rot     => 0x17,        xderef  => 0x18,
+
+       abs     => 0x19,        and     => 0x1a,
+       div     => 0x1b,        minus   => 0x1c,
+       mod     => 0x1d,        mul     => 0x1e,
+       neg     => 0x1f,        not     => 0x20,
+       or      => 0x21,        plus    => 0x22,
+       shl     => 0x24,        shr     => 0x25,
+       shra    => 0x26,        xor     => 0x27,
+       );
+
+    my %DW_OP_complex = (      # used in specific subroutines
+       constu          => 0x10,        # uleb128
+       consts          => 0x11,        # sleb128
+       plus_uconst     => 0x23,        # uleb128
+       lit0            => 0x30,        # add 0-31 to opcode
+       reg0            => 0x50,        # add 0-31 to opcode
+       breg0           => 0x70,        # add 0-31 to opcole, sleb128
+       regx            => 0x90,        # uleb28
+       fbreg           => 0x91,        # sleb128
+       bregx           => 0x92,        # uleb128, sleb128
+       piece           => 0x93,        # uleb128
+       );
+
+    # Following constants are defined in x86_64 ABI supplement, for
+    # example available at https://www.uclibc.org/docs/psABI-x86_64.pdf,
+    # see section 3.7 "Stack Unwind Algorithm".
+    my %DW_reg_idx = (
+       "%rax"=>0,  "%rdx"=>1,  "%rcx"=>2,  "%rbx"=>3,
+       "%rsi"=>4,  "%rdi"=>5,  "%rbp"=>6,  "%rsp"=>7,
+       "%r8" =>8,  "%r9" =>9,  "%r10"=>10, "%r11"=>11,
+       "%r12"=>12, "%r13"=>13, "%r14"=>14, "%r15"=>15
+       );
+
+    my ($cfa_reg, $cfa_rsp);
+    my @cfa_stack;
+
+    # [us]leb128 format is variable-length integer representation base
+    # 2^128, with most significant bit of each byte being 0 denoting
+    # *last* most significant digit. See "Variable Length Data" in the
+    # DWARF specification, numbered 7.6 at least in versions 3 and 4.
+    sub sleb128 {
+       use integer;    # get right shift extend sign
+
+       my $val = shift;
+       my $sign = ($val < 0) ? -1 : 0;
+       my @ret = ();
+
+       while(1) {
+           push @ret, $val&0x7f;
+
+           # see if remaining bits are same and equal to most
+           # significant bit of the current digit, if so, it's
+           # last digit...
+           last if (($val>>6) == $sign);
+
+           @ret[-1] |= 0x80;
+           $val >>= 7;
+       }
+
+       return @ret;
+    }
+    sub uleb128 {
+       my $val = shift;
+       my @ret = ();
+
+       while(1) {
+           push @ret, $val&0x7f;
+
+           # see if it's last significant digit...
+           last if (($val >>= 7) == 0);
+
+           @ret[-1] |= 0x80;
+       }
+
+       return @ret;
+    }
+    sub const {
+       my $val = shift;
+
+       if ($val >= 0 && $val < 32) {
+            return ($DW_OP_complex{lit0}+$val);
+       }
+       return ($DW_OP_complex{consts}, sleb128($val));
+    }
+    sub reg {
+       my $val = shift;
+
+       return if ($val !~ m/^(%r\w+)(?:([\+\-])((?:0x)?[0-9a-f]+))?/);
+
+       my $reg = $DW_reg_idx{$1};
+       my $off = eval ("0 $2 $3");
+
+       return (($DW_OP_complex{breg0} + $reg), sleb128($off));
+       # Yes, we use DW_OP_bregX+0 to push register value and not
+       # DW_OP_regX, because latter would require even DW_OP_piece,
+       # which would be a waste under the circumstances. If you have
+       # to use DWP_OP_reg, use "regx:N"...
+    }
+    sub cfa_expression {
+       my $line = shift;
+       my @ret;
+
+       foreach my $token (split(/,\s*/,$line)) {
+           if ($token =~ /^%r/) {
+               push @ret,reg($token);
+           } elsif ($token =~ /((?:0x)?[0-9a-f]+)\((%r\w+)\)/) {
+               push @ret,reg("$2+$1");
+           } elsif ($token =~ /(\w+):(\-?(?:0x)?[0-9a-f]+)(U?)/i) {
+               my $i = 1*eval($2);
+               push @ret,$DW_OP_complex{$1}, ($3 ? uleb128($i) : sleb128($i));
+           } elsif (my $i = 1*eval($token) or $token eq "0") {
+               if ($token =~ /^\+/) {
+                   push @ret,$DW_OP_complex{plus_uconst},uleb128($i);
+               } else {
+                   push @ret,const($i);
+               }
+           } else {
+               push @ret,$DW_OP_simple{$token};
+           }
+       }
+
+       # Finally we return DW_CFA_def_cfa_expression, 15, followed by
+       # length of the expression and of course the expression itself.
+       return (15,scalar(@ret),@ret);
+    }
+    sub re {
+       my      ($class, $line) = @_;
+       my      $self = {};
+       my      $ret;
+
+       if ($$line =~ s/^\s*\.cfi_(\w+)\s*//) {
+           bless $self,$class;
+           $ret = $self;
+           undef $self->{value};
+           my $dir = $1;
+
+           SWITCH: for ($dir) {
+           # What is $cfa_rsp? Effectively it's difference between %rsp
+           # value and current CFA, Canonical Frame Address, which is
+           # why it starts with -8. Recall that CFA is top of caller's
+           # stack...
+           /startproc/ && do { ($cfa_reg, $cfa_rsp) = ("%rsp", -8); last; };
+           /endproc/   && do { ($cfa_reg, $cfa_rsp) = ("%rsp",  0);
+                               # .cfi_remember_state directives that are not
+                               # matched with .cfi_restore_state are
+                               # unnecessary.
+                               die "unpaired .cfi_remember_state" if (@cfa_stack);
+                               last;
+                             };
+           /def_cfa_register/
+                       && do { $cfa_reg = $$line; last; };
+           /def_cfa_offset/
+                       && do { $cfa_rsp = -1*eval($$line) if ($cfa_reg eq "%rsp");
+                               last;
+                             };
+           /adjust_cfa_offset/
+                       && do { $cfa_rsp -= 1*eval($$line) if ($cfa_reg eq "%rsp");
+                               last;
+                             };
+           /def_cfa/   && do { if ($$line =~ /(%r\w+)\s*,\s*(.+)/) {
+                                   $cfa_reg = $1;
+                                   $cfa_rsp = -1*eval($2) if ($cfa_reg eq "%rsp");
+                               }
+                               last;
+                             };
+           /push/      && do { $dir = undef;
+                               $cfa_rsp -= 8;
+                               if ($cfa_reg eq "%rsp") {
+                                   $self->{value} = ".cfi_adjust_cfa_offset\t8\n";
+                               }
+                               $self->{value} .= ".cfi_offset\t$$line,$cfa_rsp";
+                               last;
+                             };
+           /pop/       && do { $dir = undef;
+                               $cfa_rsp += 8;
+                               if ($cfa_reg eq "%rsp") {
+                                   $self->{value} = ".cfi_adjust_cfa_offset\t-8\n";
+                               }
+                               $self->{value} .= ".cfi_restore\t$$line";
+                               last;
+                             };
+           /cfa_expression/
+                       && do { $dir = undef;
+                               $self->{value} = ".cfi_escape\t" .
+                                       join(",", map(sprintf("0x%02x", $_),
+                                                     cfa_expression($$line)));
+                               last;
+                             };
+           /remember_state/
+                       && do { push @cfa_stack, [$cfa_reg, $cfa_rsp];
+                               last;
+                             };
+           /restore_state/
+                       && do { ($cfa_reg, $cfa_rsp) = @{pop @cfa_stack};
+                               last;
+                             };
+           }
+
+           $self->{value} = ".cfi_$dir\t$$line" if ($dir);
+
+           $$line = "";
+       }
+
+       return $ret;
+    }
+    sub out {
+       my $self = shift;
+       return ($elf ? $self->{value} : undef);
+    }
+}
 { package directive;   # pick up directives, which start with .
     sub re {
        my      ($class, $line) = @_;
        my      $self = {};
        my      $ret;
        my      $dir;
-       my      %opcode =       # lea 2f-1f(%rip),%dst; 1: nop; 2:
-               (       "%rax"=>0x01058d48,     "%rcx"=>0x010d8d48,
-                       "%rdx"=>0x01158d48,     "%rbx"=>0x011d8d48,
-                       "%rsp"=>0x01258d48,     "%rbp"=>0x012d8d48,
-                       "%rsi"=>0x01358d48,     "%rdi"=>0x013d8d48,
-                       "%r8" =>0x01058d4c,     "%r9" =>0x010d8d4c,
-                       "%r10"=>0x01158d4c,     "%r11"=>0x011d8d4c,
-                       "%r12"=>0x01258d4c,     "%r13"=>0x012d8d4c,
-                       "%r14"=>0x01358d4c,     "%r15"=>0x013d8d4c      );
+
+       # chain-call to cfi_directive
+       $ret = cfi_directive->re($line) and return $ret;
 
        if ($$line =~ /^\s*(\.\w+)/) {
            bless $self,$class;
@@ -481,12 +735,6 @@ my %globals;
            $$line = substr($$line,@+[0]); $$line =~ s/^\s+//;
 
            SWITCH: for ($dir) {
-               /\.picmeup/ && do { if ($$line =~ /(%r[\w]+)/i) {
-                                       $dir="\t.long";
-                                       $$line=sprintf "0x%x,0x90000000",$opcode{$1};
-                                   }
-                                   last;
-                                 };
                /\.global|\.globl|\.extern/
                            && do { $globals{$$line} = $prefix . $$line;
                                    $$line = $globals{$$line} if ($prefix);
@@ -644,7 +892,7 @@ my %globals;
                                                        $var=~s/^(0b[0-1]+)/oct($1)/eig;
                                                        $var=~s/^0x([0-9a-f]+)/0$1h/ig if ($masm);
                                                        if ($sz eq "D" && ($current_segment=~/.[px]data/ || $dir eq ".rva"))
-                                                       { $var=~s/([_a-z\$\@][_a-z0-9\$\@]*)/$nasm?"$1 wrt ..imagebase":"imagerel $1"/egi; }
+                                                       { $var=~s/^([_a-z\$\@][_a-z0-9\$\@]*)/$nasm?"$1 wrt ..imagebase":"imagerel $1"/egi; }
                                                        $var;
                                                    };
 
@@ -691,15 +939,6 @@ my %globals;
     }
 }
 
-sub rex {
- my $opcode=shift;
- my ($dst,$src,$rex)=@_;
-
-   $rex|=0x04 if($dst>=8);
-   $rex|=0x01 if($src>=8);
-   push @$opcode,($rex|0x40) if ($rex);
-}
-
 # Upon initial x86_64 introduction SSE>2 extensions were not introduced
 # yet. In order not to be bothered by tracing exact assembler versions,
 # but at the same time to provide a bare security minimum of AES-NI, we
@@ -710,6 +949,15 @@ sub rex {
 my %regrm = (  "%eax"=>0, "%ecx"=>1, "%edx"=>2, "%ebx"=>3,
                "%esp"=>4, "%ebp"=>5, "%esi"=>6, "%edi"=>7      );
 
+sub rex {
+ my $opcode=shift;
+ my ($dst,$src,$rex)=@_;
+
+   $rex|=0x04 if($dst>=8);
+   $rex|=0x01 if($src>=8);
+   push @$opcode,($rex|0x40) if ($rex);
+}
+
 my $movq = sub {       # elderly gas can't handle inter-register movq
   my $arg = shift;
   my @opcode=(0x66);
@@ -833,6 +1081,10 @@ my $rdseed = sub {
     }
 };
 
+# Not all AVX-capable assemblers recognize AMD XOP extension. Since we
+# are using only two instructions hand-code them in order to be excused
+# from chasing assembler versions...
+
 sub rxb {
  my $opcode=shift;
  my ($dst,$src1,$src2,$rxb)=@_;
@@ -872,10 +1124,15 @@ my $vprotq = sub {
     }
 };
 
+# Intel Control-flow Enforcement Technology extension. All functions and
+# indirect branch targets will have to start with this instruction...
+
 my $endbranch = sub {
     (0xf3,0x0f,0x1e,0xfa);
 };
 
+########################################################################
+
 if ($nasm) {
     print <<___;
 default        rel
@@ -1004,7 +1261,7 @@ close STDOUT;
 # the area above user stack pointer in true asynchronous manner...
 #
 # All the above means that if assembler programmer adheres to Unix
-# register and stack layout, but disregards the "red zone" existense,
+# register and stack layout, but disregards the "red zone" existence,
 # it's possible to use following prologue and epilogue to "gear" from
 # Unix to Win64 ABI in leaf functions with not more than 6 arguments.
 #
@@ -1062,6 +1319,7 @@ close STDOUT;
 #      movq    -16(%rcx),%rbx
 #      movq    -8(%rcx),%r15
 #      movq    %rcx,%rsp       # restore original rsp
+# magic_epilogue:
 #      ret
 # .size function,.-function
 #
@@ -1074,11 +1332,16 @@ close STDOUT;
 # EXCEPTION_DISPOSITION handler (EXCEPTION_RECORD *rec,ULONG64 frame,
 #              CONTEXT *context,DISPATCHER_CONTEXT *disp)
 # {    ULONG64 *rsp = (ULONG64 *)context->Rax;
-#      if (context->Rip >= magic_point)
-#      {   rsp = ((ULONG64 **)context->Rsp)[0];
-#          context->Rbp = rsp[-3];
-#          context->Rbx = rsp[-2];
-#          context->R15 = rsp[-1];
+#      ULONG64  rip = context->Rip;
+#
+#      if (rip >= magic_point)
+#      {   rsp = (ULONG64 *)context->Rsp;
+#          if (rip < magic_epilogue)
+#          {   rsp = (ULONG64 *)rsp[0];
+#              context->Rbp = rsp[-3];
+#              context->Rbx = rsp[-2];
+#              context->R15 = rsp[-1];
+#          }
 #      }
 #      context->Rsp = (ULONG64)rsp;
 #      context->Rdi = rsp[1];
@@ -1170,16 +1433,15 @@ close STDOUT;
 # instruction and reflecting it in finer grade unwind logic in handler.
 # After all, isn't it why it's called *language-specific* handler...
 #
-# Attentive reader can notice that exceptions would be mishandled in
-# auto-generated "gear" epilogue. Well, exception effectively can't
-# occur there, because if memory area used by it was subject to
-# segmentation violation, then it would be raised upon call to the
-# function (and as already mentioned be accounted to caller, which is
-# not a problem). If you're still not comfortable, then define tail
-# "magic point" just prior ret instruction and have handler treat it...
+# SE handlers are also involved in unwinding stack when executable is
+# profiled or debugged. Profiling implies additional limitations that
+# are too subtle to discuss here. For now it's sufficient to say that
+# in order to simplify handlers one should either a) offload original
+# %rsp to stack (like discussed above); or b) if you have a register to
+# spare for frame pointer, choose volatile one.
 #
 # (*)  Note that we're talking about run-time, not debug-time. Lack of
 #      unwind information makes debugging hard on both Windows and
-#      Unix. "Unlike" referes to the fact that on Unix signal handler
+#      Unix. "Unlike" refers to the fact that on Unix signal handler
 #      will always be invoked, core dumped and appropriate exit code
 #      returned to parent (for user notification).