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
38 // clang-format off
39 #define FOR_EACH_SRC_NOTE_TYPE(M) \
40 M(SRC_NULL, "null", 0) /* Terminates a note vector. */ \
41 M(SRC_IF, "if", 0) /* JSOP_IFEQ bytecode is from an if-then. */ \
42 M(SRC_IF_ELSE, "if-else", 1) /* JSOP_IFEQ bytecode is from an if-then-else. */ \
43 M(SRC_COND, "cond", 1) /* JSOP_IFEQ is from conditional ?: operator. */ \
44 M(SRC_FOR, "for", 3) /* JSOP_NOP or JSOP_POP in for(;;) loop head. */ \
45 M(SRC_WHILE, "while", 1) /* JSOP_GOTO to for or while loop condition from before \
46 loop, else JSOP_NOP at top of do-while loop. */ \
47 M(SRC_FOR_IN, "for-in", 1) /* JSOP_GOTO to for-in loop condition from before \
48 loop. */ \
49 M(SRC_FOR_OF, "for-of", 1) /* JSOP_GOTO to for-of loop condition from before \
50 loop. */ \
51 M(SRC_CONTINUE, "continue", 0) /* JSOP_GOTO is a continue. */ \
52 M(SRC_BREAK, "break", 0) /* JSOP_GOTO is a break. */ \
53 M(SRC_BREAK2LABEL, "break2label", 0) /* JSOP_GOTO for 'break label'. */ \
54 M(SRC_SWITCHBREAK, "switchbreak", 0) /* JSOP_GOTO is a break in a switch. */ \
55 M(SRC_TABLESWITCH, "tableswitch", 1) /* JSOP_TABLESWITCH; offset points to end of switch. */ \
56 M(SRC_CONDSWITCH, "condswitch", 2) /* JSOP_CONDSWITCH; 1st offset points to end of switch, \
57 2nd points to first JSOP_CASE. */ \
58 M(SRC_NEXTCASE, "nextcase", 1) /* Distance forward from one CASE in a CONDSWITCH to \
59 the next. */ \
60 M(SRC_ASSIGNOP, "assignop", 0) /* += or another assign-op follows. */ \
61 M(SRC_CLASS_SPAN, "class", 2) /* The starting and ending offsets for the class, used \
62 for toString correctness for default ctors. */ \
63 M(SRC_TRY, "try", 1) /* JSOP_TRY, offset points to goto at the end of the \
64 try block. */ \
65 /* All notes above here are "gettable". See SN_IS_GETTABLE below. */ \
66 M(SRC_COLSPAN, "colspan", 1) /* Number of columns this opcode spans. */ \
67 M(SRC_NEWLINE, "newline", 0) /* Bytecode follows a source newline. */ \
68 M(SRC_SETLINE, "setline", 1) /* A file-absolute source line number note. */ \
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 // clang-format on
74
75 enum SrcNoteType {
76 #define DEFINE_SRC_NOTE_TYPE(sym, name, arity) sym,
77 FOR_EACH_SRC_NOTE_TYPE(DEFINE_SRC_NOTE_TYPE)
78 #undef DEFINE_SRC_NOTE_TYPE
79
80 SRC_LAST,
81 SRC_LAST_GETTABLE = SRC_TRY
82 };
83
84 static_assert(SRC_XDELTA == 24, "SRC_XDELTA should be 24");
85
86 /* A source note array is terminated by an all-zero element. */
SN_MAKE_TERMINATOR(jssrcnote * sn)87 inline void SN_MAKE_TERMINATOR(jssrcnote* sn) { *sn = SRC_NULL; }
88
SN_IS_TERMINATOR(jssrcnote * sn)89 inline bool SN_IS_TERMINATOR(jssrcnote* sn) { return *sn == SRC_NULL; }
90
91 } // namespace js
92
93 #define SN_TYPE_BITS 5
94 #define SN_DELTA_BITS 3
95 #define SN_XDELTA_BITS 6
96 #define SN_TYPE_MASK (JS_BITMASK(SN_TYPE_BITS) << SN_DELTA_BITS)
97 #define SN_DELTA_MASK ((ptrdiff_t)JS_BITMASK(SN_DELTA_BITS))
98 #define SN_XDELTA_MASK ((ptrdiff_t)JS_BITMASK(SN_XDELTA_BITS))
99
100 #define SN_MAKE_NOTE(sn, t, d) \
101 (*(sn) = (jssrcnote)(((t) << SN_DELTA_BITS) | ((d)&SN_DELTA_MASK)))
102 #define SN_MAKE_XDELTA(sn, d) \
103 (*(sn) = (jssrcnote)((SRC_XDELTA << SN_DELTA_BITS) | ((d)&SN_XDELTA_MASK)))
104
105 #define SN_IS_XDELTA(sn) ((*(sn) >> SN_DELTA_BITS) >= SRC_XDELTA)
106 #define SN_TYPE(sn) \
107 ((js::SrcNoteType)(SN_IS_XDELTA(sn) ? SRC_XDELTA : *(sn) >> SN_DELTA_BITS))
108 #define SN_SET_TYPE(sn, type) SN_MAKE_NOTE(sn, type, SN_DELTA(sn))
109 #define SN_IS_GETTABLE(sn) (SN_TYPE(sn) <= SRC_LAST_GETTABLE)
110
111 #define SN_DELTA(sn) \
112 ((ptrdiff_t)(SN_IS_XDELTA(sn) ? *(sn)&SN_XDELTA_MASK : *(sn)&SN_DELTA_MASK))
113 #define SN_SET_DELTA(sn, delta) \
114 (SN_IS_XDELTA(sn) ? SN_MAKE_XDELTA(sn, delta) \
115 : SN_MAKE_NOTE(sn, SN_TYPE(sn), delta))
116
117 #define SN_DELTA_LIMIT ((ptrdiff_t)JS_BIT(SN_DELTA_BITS))
118 #define SN_XDELTA_LIMIT ((ptrdiff_t)JS_BIT(SN_XDELTA_BITS))
119
120 /*
121 * Offset fields follow certain notes and are frequency-encoded: an offset in
122 * [0,0x7f] consumes one byte, an offset in [0x80,0x7fffffff] takes four, and
123 * the high bit of the first byte is set.
124 */
125 #define SN_4BYTE_OFFSET_FLAG 0x80
126 #define SN_4BYTE_OFFSET_MASK 0x7f
127
128 #define SN_OFFSET_BITS 31
129 #define SN_MAX_OFFSET (((size_t)1 << SN_OFFSET_BITS) - 1)
130
SN_REPRESENTABLE_OFFSET(ptrdiff_t offset)131 inline bool SN_REPRESENTABLE_OFFSET(ptrdiff_t offset) {
132 return 0 <= offset && size_t(offset) <= SN_MAX_OFFSET;
133 }
134
135 /*
136 * SRC_COLSPAN values represent changes to the column number. Colspans are
137 * signed: negative changes arise in describing constructs like for(;;) loops,
138 * that generate code in non-source order. (Negative colspans also have a
139 * history of indicating bugs in updating ParseNodes' source locations.)
140 *
141 * We store colspans using the same variable-length encoding as offsets,
142 * described above. However, unlike offsets, colspans are signed, so we truncate
143 * colspans (SN_COLSPAN_TO_OFFSET) for storage as offsets, and sign-extend
144 * offsets into colspans when we read them (SN_OFFSET_TO_COLSPAN).
145 */
146 #define SN_COLSPAN_SIGN_BIT (1 << (SN_OFFSET_BITS - 1))
147 #define SN_MIN_COLSPAN (-SN_COLSPAN_SIGN_BIT)
148 #define SN_MAX_COLSPAN (SN_COLSPAN_SIGN_BIT - 1)
149
SN_REPRESENTABLE_COLSPAN(ptrdiff_t colspan)150 inline bool SN_REPRESENTABLE_COLSPAN(ptrdiff_t colspan) {
151 return SN_MIN_COLSPAN <= colspan && colspan <= SN_MAX_COLSPAN;
152 }
153
SN_OFFSET_TO_COLSPAN(ptrdiff_t offset)154 inline ptrdiff_t SN_OFFSET_TO_COLSPAN(ptrdiff_t offset) {
155 // There should be no bits set outside the field we're going to sign-extend.
156 MOZ_ASSERT(!(offset & ~((1U << SN_OFFSET_BITS) - 1)));
157 // Sign-extend the least significant SN_OFFSET_BITS bits.
158 return (offset ^ SN_COLSPAN_SIGN_BIT) - SN_COLSPAN_SIGN_BIT;
159 }
160
SN_COLSPAN_TO_OFFSET(ptrdiff_t colspan)161 inline ptrdiff_t SN_COLSPAN_TO_OFFSET(ptrdiff_t colspan) {
162 // Truncate the two's complement colspan, for storage as an offset.
163 ptrdiff_t offset = colspan & ((1U << SN_OFFSET_BITS) - 1);
164 // When we read this back, we'd better get the value we stored.
165 MOZ_ASSERT(SN_OFFSET_TO_COLSPAN(offset) == colspan);
166 return offset;
167 }
168
169 #define SN_LENGTH(sn) \
170 ((js_SrcNoteSpec[SN_TYPE(sn)].arity == 0) ? 1 : js::SrcNoteLength(sn))
171 #define SN_NEXT(sn) ((sn) + SN_LENGTH(sn))
172
173 struct JSSrcNoteSpec {
174 const char* name; /* name for disassembly/debugging output */
175 int8_t arity; /* number of offset operands */
176 };
177
178 extern JS_FRIEND_DATA const JSSrcNoteSpec js_SrcNoteSpec[];
179
180 namespace js {
181
182 extern JS_FRIEND_API unsigned SrcNoteLength(jssrcnote* sn);
183
184 /*
185 * Get and set the offset operand identified by which (0 for the first, etc.).
186 */
187 extern JS_FRIEND_API ptrdiff_t GetSrcNoteOffset(jssrcnote* sn, unsigned which);
188
189 } // namespace js
190
191 #endif /* frontend_SourceNotes_h */
192