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1 | package # hide hide not just from PAUSE but from everyone - shoo shoo shooooo! |
2 | Devel::PeekPoke::PP; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
7 | use 5.008001; # because 5.6 doesn't have B::PV::object_2svref |
8 | |
9 | use Carp; |
10 | use Config; |
11 | use Devel::PeekPoke::Constants qw/PTR_SIZE PTR_PACK_TYPE/; |
12 | use B (); # for B::PV |
13 | |
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14 | use constant { |
15 | _MAX_ADDR => 'FF' x PTR_SIZE, |
16 | _PERLVERSION => "$]", # we do not support every perl, as we rely on the implementation of SV/SvPV |
17 | }; |
18 | |
19 | BEGIN { |
20 | # we know we start from 5.8.1 |
21 | if ( (_PERLVERSION =~ /^5\.(\d{3})/)[0] % 2 ) { |
22 | die "@{[ __PACKAGE__ ]} does not function on development perl versions (by design)\n"; |
23 | } |
24 | elsif (_PERLVERSION < 5.010) { |
25 | constant->import({ |
26 | _SV_SIZE => PTR_SIZE + 4 + 4, # SvANY + 32bit refcnt + 32bit flags |
27 | _XPV_SIZE => PTR_SIZE + $Config{sizesize} + $Config{sizesize}, # PVX ptr + cur + len |
28 | _SVU_OFFSET => 0, |
29 | }); |
30 | } |
31 | elsif (_PERLVERSION < 5.016) { |
32 | constant->import({ |
33 | _SV_SIZE => PTR_SIZE + 4 + 4 + $Config{ivsize}, # SvANY + 32bit refcnt + 32bit flags + SV_U |
34 | _XPV_SIZE => undef, # it isn't really undefined, we just do not care |
35 | _SVU_OFFSET => PTR_SIZE + 4 + 4, |
36 | }); |
37 | } |
38 | else { |
39 | # do not take any chanes with not-yet-released perls - things may change |
40 | die "@{[ __PACKAGE__ ]} does not *yet* support this perl $], please file a bugreport (it is very very easy to fix)\n"; |
41 | } |
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42 | } |
43 | |
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44 | sub _pack_address { |
45 | my ($digits) = (defined $_[0] and $_[0] =~ /^(\d+)$/) |
46 | or croak "Invalid address '$_[0]' - expecting an integer"; |
47 | |
48 | my $p = pack(PTR_PACK_TYPE, $_[0]); |
49 | |
50 | # FIXME - is there a saner way to check for overflows? |
51 | no warnings 'portable'; # hex() with a 64bit value |
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52 | croak "Your system does not support addresses larger than 0x@{[ _MAX_ADDR ]}, you supplied $digits" |
53 | if ( $_[0] > hex(_MAX_ADDR) or uc(unpack('H*', $p)) eq _MAX_ADDR ); |
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54 | |
55 | return $p; |
56 | } |
57 | |
58 | sub peek { |
59 | #my($location, $len_bytes) = @_; |
60 | croak "Peek where and how much?" unless (defined $_[0]) and $_[1]; |
61 | unpack "P$_[1]", _pack_address($_[0]); |
62 | } |
63 | |
64 | # this implementation is based on (a portably written version of) |
65 | # http://www.perlmonks.org/?node_id=379428 |
66 | # there should be a much simpler way according to Reini Urban, but I |
67 | # was not able to make it work: https://gist.github.com/1151345 |
68 | sub poke { |
69 | my($location, $bytes) = @_; |
70 | croak "Poke where and what?" unless (defined $location) and (defined $bytes); |
71 | |
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72 | # sanity check and properly pack address |
73 | my $addr = _pack_address($location); |
74 | |
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75 | # sanity check is (imho) warranted as described here: |
76 | # http://blogs.perl.org/users/aristotle/2011/08/utf8-flag.html#comment-36499 |
77 | if (utf8::is_utf8($bytes) and $bytes =~ /([^\x00-\x7F])/) { |
78 | croak( ord($1) > 255 |
79 | ? "Expecting a byte string, but received characters" |
80 | : "Expecting a byte string, but received what looks like *possible* characters, please utf8_downgrade the input" |
81 | ); |
82 | } |
83 | |
84 | # this should be constant once we pass the regex check above... right? |
85 | my $len = length($bytes); |
86 | |
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87 | # construct a B::PV object, backed by a SV/SvPV to a dummy string length($bytes) |
88 | # long, and substitute $location as the actual string storage |
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89 | # we specifically use the same length so we do not have to deal with resizing |
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90 | my $dummy = 'X' x $len; |
91 | my $dummy_addr = \$dummy + 0; |
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92 | |
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93 | my $ghost_sv_contents = peek($dummy_addr, _SV_SIZE); |
94 | |
95 | if (_XPV_SIZE) { # 5.8 xpv stuff |
96 | my $xpv_addr = unpack(PTR_PACK_TYPE, peek($dummy_addr, PTR_SIZE) ); |
97 | my $xpv_contents = peek( $xpv_addr, _XPV_SIZE ); # we do not care about cur/len (they will be the same) |
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98 | |
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99 | substr( $xpv_contents, 0, PTR_SIZE ) = $addr; # replace pvx in xpv with the "string buffer" location |
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100 | substr( $ghost_sv_contents, 0, PTR_SIZE) = pack ('P', $xpv_contents ); # replace xpv in sv |
101 | } |
102 | else { # new style 5.10+ SVs |
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103 | substr( $ghost_sv_contents, _SVU_OFFSET, PTR_SIZE ) = $addr; |
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104 | } |
105 | |
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106 | my $ghost_string_ref = bless( \ unpack( |
107 | PTR_PACK_TYPE, |
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108 | # it is crucial to create a copy of $sv_contents, and work with a temporary |
109 | # memory location. Otherwise perl memory allocation will kick in and wreak |
110 | # considerable havoc culminating with an inevitable segfault |
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111 | do { no warnings 'pack'; pack( 'P', $ghost_sv_contents.'' ) }, |
112 | ), 'B::PV' )->object_2svref; |
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113 | |
114 | # now when we write to the newly created "string" we are actually writing |
115 | # to $location |
116 | # note we HAVE to use lvalue substr - a plain assignment will add a \0 |
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117 | # |
118 | # Also in order to keep threading on perl 5.8.x happy we *have* to perform this |
119 | # in a string eval. I don't have the slightest idea why :) |
120 | eval 'substr($$ghost_string_ref, 0, $len) = $bytes'; |
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121 | |
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122 | return $len; |
123 | } |
124 | |
125 | 1; |