1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
2 * vim: set ts=8 sts=4 et sw=4 tw=99:
3 * This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6
7 #ifndef frontend_SourceNotes_h
8 #define frontend_SourceNotes_h
9
10 #include <stdint.h>
11
12 #include "jstypes.h"
13
14 typedef uint8_t jssrcnote;
15
16 namespace js {
17
18 /*
19 * Source notes generated along with bytecode for decompiling and debugging.
20 * A source note is a uint8_t with 5 bits of type and 3 of offset from the pc
21 * of the previous note. If 3 bits of offset aren't enough, extended delta
22 * notes (SRC_XDELTA) consisting of 2 set high order bits followed by 6 offset
23 * bits are emitted before the next note. Some notes have operand offsets
24 * encoded immediately after them, in note bytes or byte-triples.
25 *
26 * Source Note Extended Delta
27 * +7-6-5-4-3+2-1-0+ +7-6-5+4-3-2-1-0+
28 * |note-type|delta| |1 1| ext-delta |
29 * +---------+-----+ +---+-----------+
30 *
31 * At most one "gettable" note (i.e., a note of type other than SRC_NEWLINE,
32 * SRC_COLSPAN, SRC_SETLINE, and SRC_XDELTA) applies to a given bytecode.
33 *
34 * NB: the js_SrcNoteSpec array in BytecodeEmitter.cpp is indexed by this
35 * enum, so its initializers need to match the order here.
36 *
37 * Don't forget to update XDR_BYTECODE_VERSION in vm/Xdr.h for all such
38 * incompatible source note or other bytecode changes.
39 */
40 #define FOR_EACH_SRC_NOTE_TYPE(M) \
41 M(SRC_NULL, "null", 0) /* Terminates a note vector. */ \
42 M(SRC_IF, "if", 0) /* JSOP_IFEQ bytecode is from an if-then. */ \
43 M(SRC_IF_ELSE, "if-else", 1) /* JSOP_IFEQ bytecode is from an if-then-else. */ \
44 M(SRC_COND, "cond", 1) /* JSOP_IFEQ is from conditional ?: operator. */ \
45 M(SRC_FOR, "for", 3) /* JSOP_NOP or JSOP_POP in for(;;) loop head. */ \
46 M(SRC_WHILE, "while", 1) /* JSOP_GOTO to for or while loop condition from before \
47 loop, else JSOP_NOP at top of do-while loop. */ \
48 M(SRC_FOR_IN, "for-in", 1) /* JSOP_GOTO to for-in loop condition from before \
49 loop. */ \
50 M(SRC_FOR_OF, "for-of", 1) /* JSOP_GOTO to for-of loop condition from before \
51 loop. */ \
52 M(SRC_CONTINUE, "continue", 0) /* JSOP_GOTO is a continue. */ \
53 M(SRC_BREAK, "break", 0) /* JSOP_GOTO is a break. */ \
54 M(SRC_BREAK2LABEL, "break2label", 0) /* JSOP_GOTO for 'break label'. */ \
55 M(SRC_SWITCHBREAK, "switchbreak", 0) /* JSOP_GOTO is a break in a switch. */ \
56 M(SRC_TABLESWITCH, "tableswitch", 1) /* JSOP_TABLESWITCH; offset points to end of switch. */ \
57 M(SRC_CONDSWITCH, "condswitch", 2) /* JSOP_CONDSWITCH; 1st offset points to end of switch, \
58 2nd points to first JSOP_CASE. */ \
59 M(SRC_NEXTCASE, "nextcase", 1) /* Distance forward from one CASE in a CONDSWITCH to \
60 the next. */ \
61 M(SRC_ASSIGNOP, "assignop", 0) /* += or another assign-op follows. */ \
62 M(SRC_TRY, "try", 1) /* JSOP_TRY, offset points to goto at the end of the \
63 try block. */ \
64 /* All notes above here are "gettable". See SN_IS_GETTABLE below. */ \
65 M(SRC_COLSPAN, "colspan", 1) /* Number of columns this opcode spans. */ \
66 M(SRC_NEWLINE, "newline", 0) /* Bytecode follows a source newline. */ \
67 M(SRC_SETLINE, "setline", 1) /* A file-absolute source line number note. */ \
68 M(SRC_UNUSED20, "unused20", 0) /* Unused. */ \
69 M(SRC_UNUSED21, "unused21", 0) /* Unused. */ \
70 M(SRC_UNUSED22, "unused22", 0) /* Unused. */ \
71 M(SRC_UNUSED23, "unused23", 0) /* Unused. */ \
72 M(SRC_XDELTA, "xdelta", 0) /* 24-31 are for extended delta notes. */
73
74 enum SrcNoteType {
75 #define DEFINE_SRC_NOTE_TYPE(sym, name, arity) sym,
76 FOR_EACH_SRC_NOTE_TYPE(DEFINE_SRC_NOTE_TYPE)
77 #undef DEFINE_SRC_NOTE_TYPE
78
79 SRC_LAST,
80 SRC_LAST_GETTABLE = SRC_TRY
81 };
82
83 static_assert(SRC_XDELTA == 24, "SRC_XDELTA should be 24");
84
85 /* A source note array is terminated by an all-zero element. */
86 inline void
SN_MAKE_TERMINATOR(jssrcnote * sn)87 SN_MAKE_TERMINATOR(jssrcnote* sn)
88 {
89 *sn = SRC_NULL;
90 }
91
92 inline bool
SN_IS_TERMINATOR(jssrcnote * sn)93 SN_IS_TERMINATOR(jssrcnote* sn)
94 {
95 return *sn == SRC_NULL;
96 }
97
98 } // namespace js
99
100 #define SN_TYPE_BITS 5
101 #define SN_DELTA_BITS 3
102 #define SN_XDELTA_BITS 6
103 #define SN_TYPE_MASK (JS_BITMASK(SN_TYPE_BITS) << SN_DELTA_BITS)
104 #define SN_DELTA_MASK ((ptrdiff_t)JS_BITMASK(SN_DELTA_BITS))
105 #define SN_XDELTA_MASK ((ptrdiff_t)JS_BITMASK(SN_XDELTA_BITS))
106
107 #define SN_MAKE_NOTE(sn,t,d) (*(sn) = (jssrcnote) \
108 (((t) << SN_DELTA_BITS) \
109 | ((d) & SN_DELTA_MASK)))
110 #define SN_MAKE_XDELTA(sn,d) (*(sn) = (jssrcnote) \
111 ((SRC_XDELTA << SN_DELTA_BITS) \
112 | ((d) & SN_XDELTA_MASK)))
113
114 #define SN_IS_XDELTA(sn) ((*(sn) >> SN_DELTA_BITS) >= SRC_XDELTA)
115 #define SN_TYPE(sn) ((js::SrcNoteType)(SN_IS_XDELTA(sn) \
116 ? SRC_XDELTA \
117 : *(sn) >> SN_DELTA_BITS))
118 #define SN_SET_TYPE(sn,type) SN_MAKE_NOTE(sn, type, SN_DELTA(sn))
119 #define SN_IS_GETTABLE(sn) (SN_TYPE(sn) <= SRC_LAST_GETTABLE)
120
121 #define SN_DELTA(sn) ((ptrdiff_t)(SN_IS_XDELTA(sn) \
122 ? *(sn) & SN_XDELTA_MASK \
123 : *(sn) & SN_DELTA_MASK))
124 #define SN_SET_DELTA(sn,delta) (SN_IS_XDELTA(sn) \
125 ? SN_MAKE_XDELTA(sn, delta) \
126 : SN_MAKE_NOTE(sn, SN_TYPE(sn), delta))
127
128 #define SN_DELTA_LIMIT ((ptrdiff_t)JS_BIT(SN_DELTA_BITS))
129 #define SN_XDELTA_LIMIT ((ptrdiff_t)JS_BIT(SN_XDELTA_BITS))
130
131 /*
132 * Offset fields follow certain notes and are frequency-encoded: an offset in
133 * [0,0x7f] consumes one byte, an offset in [0x80,0x7fffffff] takes four, and
134 * the high bit of the first byte is set.
135 */
136 #define SN_4BYTE_OFFSET_FLAG 0x80
137 #define SN_4BYTE_OFFSET_MASK 0x7f
138
139 #define SN_OFFSET_BITS 31
140 #define SN_MAX_OFFSET (((size_t) 1 << SN_OFFSET_BITS) - 1)
141
142 inline bool
SN_REPRESENTABLE_OFFSET(ptrdiff_t offset)143 SN_REPRESENTABLE_OFFSET(ptrdiff_t offset)
144 {
145 return 0 <= offset && size_t(offset) <= SN_MAX_OFFSET;
146 }
147
148 /*
149 * SRC_COLSPAN values represent changes to the column number. Colspans are
150 * signed: negative changes arise in describing constructs like for(;;) loops,
151 * that generate code in non-source order. (Negative colspans also have a
152 * history of indicating bugs in updating ParseNodes' source locations.)
153 *
154 * We store colspans using the same variable-length encoding as offsets,
155 * described above. However, unlike offsets, colspans are signed, so we truncate
156 * colspans (SN_COLSPAN_TO_OFFSET) for storage as offsets, and sign-extend
157 * offsets into colspans when we read them (SN_OFFSET_TO_COLSPAN).
158 */
159 #define SN_COLSPAN_SIGN_BIT (1 << (SN_OFFSET_BITS - 1))
160 #define SN_MIN_COLSPAN (-SN_COLSPAN_SIGN_BIT)
161 #define SN_MAX_COLSPAN (SN_COLSPAN_SIGN_BIT - 1)
162
163 inline bool
SN_REPRESENTABLE_COLSPAN(ptrdiff_t colspan)164 SN_REPRESENTABLE_COLSPAN(ptrdiff_t colspan)
165 {
166 return SN_MIN_COLSPAN <= colspan && colspan <= SN_MAX_COLSPAN;
167 }
168
169 inline ptrdiff_t
SN_OFFSET_TO_COLSPAN(ptrdiff_t offset)170 SN_OFFSET_TO_COLSPAN(ptrdiff_t offset) {
171 // There should be no bits set outside the field we're going to sign-extend.
172 MOZ_ASSERT(!(offset & ~((1U << SN_OFFSET_BITS) - 1)));
173 // Sign-extend the least significant SN_OFFSET_BITS bits.
174 return (offset ^ SN_COLSPAN_SIGN_BIT) - SN_COLSPAN_SIGN_BIT;
175 }
176
177 inline ptrdiff_t
SN_COLSPAN_TO_OFFSET(ptrdiff_t colspan)178 SN_COLSPAN_TO_OFFSET(ptrdiff_t colspan) {
179 // Truncate the two's complement colspan, for storage as an offset.
180 ptrdiff_t offset = colspan & ((1U << SN_OFFSET_BITS) - 1);
181 // When we read this back, we'd better get the value we stored.
182 MOZ_ASSERT(SN_OFFSET_TO_COLSPAN(offset) == colspan);
183 return offset;
184 }
185
186 #define SN_LENGTH(sn) ((js_SrcNoteSpec[SN_TYPE(sn)].arity == 0) ? 1 \
187 : js::SrcNoteLength(sn))
188 #define SN_NEXT(sn) ((sn) + SN_LENGTH(sn))
189
190 struct JSSrcNoteSpec {
191 const char* name; /* name for disassembly/debugging output */
192 int8_t arity; /* number of offset operands */
193 };
194
195 extern JS_FRIEND_DATA(const JSSrcNoteSpec) js_SrcNoteSpec[];
196
197 namespace js {
198
199 extern JS_FRIEND_API(unsigned)
200 SrcNoteLength(jssrcnote* sn);
201
202 /*
203 * Get and set the offset operand identified by which (0 for the first, etc.).
204 */
205 extern JS_FRIEND_API(ptrdiff_t)
206 GetSrcNoteOffset(jssrcnote* sn, unsigned which);
207
208 } // namespace js
209
210 #endif /* frontend_SourceNotes_h */
211