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219d1afa | 1 | @c Copyright (C) 2016-2018 Free Software Foundation, Inc. |
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2 | @c This is part of the GAS anual. |
3 | @c For copying conditions, see the file as.texinfo | |
4 | @c man end | |
5 | ||
6 | @ifset GENERIC | |
7 | @page | |
8 | @node RISC-V-Dependent | |
9 | @chapter RISC-V Dependent Features | |
10 | @end ifset | |
11 | @ifclear GENERIC | |
12 | @node Machine Dependencies | |
13 | @chapter RISC-V Dependent Features | |
14 | @end ifclear | |
15 | ||
16 | @cindex RISC-V support | |
17 | @menu | |
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18 | * RISC-V-Options:: RISC-V Options |
19 | * RISC-V-Directives:: RISC-V Directives | |
0e35537d | 20 | * RISC-V-Formats:: RISC-V Instruction Formats |
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21 | @end menu |
22 | ||
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23 | @node RISC-V-Options |
24 | @section RISC-V Options | |
e23eba97 | 25 | |
b57e49f7 | 26 | The following table lists all available RISC-V specific options. |
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27 | |
28 | @c man begin OPTIONS | |
29 | @table @gcctabopt | |
e23eba97 | 30 | |
19683c04 PD |
31 | @cindex @samp{-fpic} option, RISC-V |
32 | @item -fpic | |
b57e49f7 | 33 | @itemx -fPIC |
19683c04 PD |
34 | Generate position-independent code |
35 | ||
36 | @cindex @samp{-fno-pic} option, RISC-V | |
37 | @item -fno-pic | |
38 | Don't generate position-independent code (default) | |
39 | ||
4f7eddc4 PD |
40 | @cindex @samp{-march=ISA} option, RISC-V |
41 | @item -march=ISA | |
2922d21d AW |
42 | Select the base isa, as specified by ISA. For example -march=rv32ima. |
43 | ||
44 | @cindex @samp{-mabi=ABI} option, RISC-V | |
45 | @item -mabi=ABI | |
46 | Selects the ABI, which is either "ilp32" or "lp64", optionally followed | |
47 | by "f", "d", or "q" to indicate single-precision, double-precision, or | |
48 | quad-precision floating-point calling convention, or none to indicate | |
49 | the soft-float calling convention. | |
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51 | @cindex @samp{-mrelax} option, RISC-V |
52 | @item -mrelax | |
53 | Take advantage of linker relaxations to reduce the number of instructions | |
54 | required to materialize symbol addresses. (default) | |
55 | ||
56 | @cindex @samp{-mno-relax} option, RISC-V | |
57 | @item -mno-relax | |
58 | Don't do linker relaxations. | |
59 | ||
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60 | @end table |
61 | @c man end | |
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62 | |
63 | @node RISC-V-Directives | |
fed44c60 | 64 | @section RISC-V Directives |
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65 | @cindex machine directives, RISC-V |
66 | @cindex RISC-V machine directives | |
67 | ||
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68 | The following table lists all available RISC-V specific directives. |
69 | ||
70 | @table @code | |
71 | ||
72 | @cindex @code{align} directive | |
73 | @item .align @var{size-log-2} | |
74 | Align to the given boundary, with the size given as log2 the number of bytes to | |
75 | align to. | |
76 | ||
77 | @cindex Data directives | |
78 | @item .half @var{value} | |
79 | @itemx .word @var{value} | |
80 | @itemx .dword @var{value} | |
81 | Emits a half-word, word, or double-word value at the current position. | |
82 | ||
83 | @cindex DTP-relative data directives | |
84 | @item .dtprelword @var{value} | |
85 | @itemx .dtpreldword @var{value} | |
86 | Emits a DTP-relative word (or double-word) at the current position. This is | |
87 | meant to be used by the compiler in shared libraries for DWARF debug info for | |
88 | thread local variables. | |
89 | ||
90 | @cindex BSS directive | |
91 | @item .bss | |
92 | Sets the current section to the BSS section. | |
93 | ||
94 | @cindex LEB128 directives | |
95 | @item .uleb128 @var{value} | |
96 | @itemx .sleb128 @var{value} | |
97 | Emits a signed or unsigned LEB128 value at the current position. This only | |
98 | accepts constant expressions, because symbol addresses can change with | |
99 | relaxation, and we don't support relocations to modify LEB128 values at link | |
100 | time. | |
101 | ||
102 | @cindex Option directive | |
103 | @cindex @code{option} directive | |
104 | @item .option @var{argument} | |
105 | Modifies RISC-V specific assembler options inline with the assembly code. | |
106 | This is used when particular instruction sequences must be assembled with a | |
107 | specific set of options. For example, since we relax addressing sequences to | |
108 | shorter GP-relative sequences when possible the initial load of GP must not be | |
109 | relaxed and should be emitted as something like | |
110 | ||
111 | @smallexample | |
112 | .option push | |
113 | .option norelax | |
114 | la gp, __global_pointer$ | |
115 | .option pop | |
116 | @end smallexample | |
117 | ||
118 | in order to produce after linker relaxation the expected | |
119 | ||
120 | @smallexample | |
121 | auipc gp, %pcrel_hi(__global_pointer$) | |
122 | addi gp, gp, %pcrel_lo(__global_pointer$) | |
123 | @end smallexample | |
124 | ||
125 | instead of just | |
126 | ||
127 | @smallexample | |
128 | addi gp, gp, 0 | |
129 | @end smallexample | |
130 | ||
131 | It's not expected that options are changed in this manner during regular use, | |
132 | but there are a handful of esoteric cases like the one above where users need | |
133 | to disable particular features of the assembler for particular code sequences. | |
134 | The complete list of option arguments is shown below: | |
135 | ||
136 | @table @code | |
137 | @item push | |
138 | @itemx pop | |
139 | Pushes or pops the current option stack. These should be used whenever | |
140 | changing an option in line with assembly code in order to ensure the user's | |
141 | command-line options are respected for the bulk of the file being assembled. | |
142 | ||
143 | @item rvc | |
144 | @itemx norvc | |
145 | Enables or disables the generation of compressed instructions. Instructions | |
146 | are opportunistically compressed by the RISC-V assembler when possible, but | |
147 | sometimes this behavior is not desirable. | |
148 | ||
149 | @item pic | |
150 | @itemx nopic | |
151 | Enables or disables position-independent code generation. Unless you really | |
152 | know what you're doing, this should only be at the top of a file. | |
153 | ||
154 | @item relax | |
155 | @itemx norelax | |
156 | Enables or disables relaxation. The RISC-V assembler and linker | |
157 | opportunistically relax some code sequences, but sometimes this behavior is not | |
158 | desirable. | |
159 | @end table | |
160 | ||
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161 | @cindex INSN directives |
162 | @item .insn @var{value} | |
163 | @itemx .insn @var{value} | |
164 | This directive permits the numeric representation of an instructions | |
165 | and makes the assembler insert the operands according to one of the | |
166 | instruction formats for @samp{.insn} (@ref{RISC-V-Formats}). | |
167 | For example, the instruction @samp{add a0, a1, a2} could be written as | |
168 | @samp{.insn r 0x33, 0, 0, a0, a1, a2}. | |
169 | ||
b57e49f7 | 170 | @end table |
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171 | |
172 | @node RISC-V-Formats | |
173 | @section Instruction Formats | |
174 | @cindex instruction formats, risc-v | |
175 | @cindex RISC-V instruction formats | |
176 | ||
177 | The RISC-V Instruction Set Manual Volume I: User-Level ISA lists 12 | |
178 | instruction formats where some of the formats have multiple variants. | |
179 | For the @samp{.insn} pseudo directive the assembler recognizes some | |
180 | of the formats. | |
181 | Typically, the most general variant of the instruction format is used | |
182 | by the @samp{.insn} directive. | |
183 | ||
184 | The following table lists the abbreviations used in the table of | |
185 | instruction formats: | |
186 | ||
187 | @display | |
188 | @multitable @columnfractions .15 .40 | |
189 | @item opcode @tab Unsigned immediate or opcode name for 7-bits opcode. | |
190 | @item opcode2 @tab Unsigned immediate or opcode name for 2-bits opcode. | |
191 | @item func7 @tab Unsigned immediate for 7-bits function code. | |
192 | @item func4 @tab Unsigned immediate for 4-bits function code. | |
193 | @item func3 @tab Unsigned immediate for 3-bits function code. | |
194 | @item func2 @tab Unsigned immediate for 2-bits function code. | |
195 | @item rd @tab Destination register number for operand x, can be GPR or FPR. | |
196 | @item rd' @tab Destination register number for operand x, | |
197 | only accept s0-s1, a0-a5, fs0-fs1 and fa0-fa5. | |
198 | @item rs1 @tab First source register number for operand x, can be GPR or FPR. | |
199 | @item rs1' @tab First source register number for operand x, | |
200 | only accept s0-s1, a0-a5, fs0-fs1 and fa0-fa5. | |
201 | @item rs2 @tab Second source register number for operand x, can be GPR or FPR. | |
202 | @item rs2' @tab Second source register number for operand x, | |
203 | only accept s0-s1, a0-a5, fs0-fs1 and fa0-fa5. | |
204 | @item simm12 @tab Sign-extended 12-bit immediate for operand x. | |
205 | @item simm20 @tab Sign-extended 20-bit immediate for operand x. | |
206 | @item simm6 @tab Sign-extended 6-bit immediate for operand x. | |
207 | @item uimm8 @tab Unsigned 8-bit immediate for operand x. | |
208 | @item symbol @tab Symbol or lable reference for operand x. | |
209 | @end multitable | |
210 | @end display | |
211 | ||
212 | The following table lists all available opcode name: | |
213 | ||
214 | @table @code | |
215 | @item C0 | |
216 | @item C1 | |
217 | @item C2 | |
218 | Opcode space for compressed instructions. | |
219 | ||
220 | @item LOAD | |
221 | Opcode space for load instructions. | |
222 | ||
223 | @item LOAD_FP | |
224 | Opcode space for floating-point load instructions. | |
225 | ||
226 | @item STORE | |
227 | Opcode space for store instructions. | |
228 | ||
229 | @item STORE_FP | |
230 | Opcode space for floating-point store instructions. | |
231 | ||
232 | @item AUIPC | |
233 | Opcode space for auipc instruction. | |
234 | ||
235 | @item LUI | |
236 | Opcode space for lui instruction. | |
237 | ||
238 | @item BRANCH | |
239 | Opcode space for branch instructions. | |
240 | ||
241 | @item JAL | |
242 | Opcode space for jal instruction. | |
243 | ||
244 | @item JALR | |
245 | Opcode space for jalr instruction. | |
246 | ||
247 | @item OP | |
248 | Opcode space for ALU instructions. | |
249 | ||
250 | @item OP_32 | |
251 | Opcode space for 32-bits ALU instructions. | |
252 | ||
253 | @item OP_IMM | |
254 | Opcode space for ALU with immediate instructions. | |
255 | ||
256 | @item OP_IMM_32 | |
257 | Opcode space for 32-bits ALU with immediate instructions. | |
258 | ||
259 | @item OP_FP | |
260 | Opcode space for floating-point operation instructions. | |
261 | ||
262 | @item MADD | |
263 | Opcode space for madd instruction. | |
264 | ||
265 | @item MSUB | |
266 | Opcode space for msub instruction. | |
267 | ||
268 | @item NMADD | |
269 | Opcode space for nmadd instruction. | |
270 | ||
271 | @item NMSUB | |
272 | Opcode space for msub instruction. | |
273 | ||
274 | @item AMO | |
275 | Opcode space for atomic memory operation instructions. | |
276 | ||
277 | @item MISC_IMM | |
278 | Opcode space for misc instructions. | |
279 | ||
280 | @item SYSTEM | |
281 | Opcode space for system instructions. | |
282 | ||
283 | @item CUSTOM_0 | |
284 | @item CUSTOM_1 | |
285 | @item CUSTOM_2 | |
286 | @item CUSTOM_3 | |
287 | Opcode space for customize instructions. | |
288 | ||
289 | @end table | |
290 | ||
291 | An instruction is two or four bytes in length and must be aligned | |
292 | on a 2 byte boundary. The first two bits of the instruction specify the | |
293 | length of the instruction, 00, 01 and 10 indicates a two byte instruction, | |
294 | 11 indicates a four byte instruction. | |
295 | ||
296 | The following table lists the RISC-V instruction formats that are available | |
297 | with the @samp{.insn} pseudo directive: | |
298 | ||
299 | @table @code | |
300 | @item R type: .insn r opcode, func3, func7, rd, rs1, rs2 | |
301 | @verbatim | |
302 | +-------+-----+-----+-------+----+-------------+ | |
303 | | func7 | rs2 | rs1 | func3 | rd | opcode | | |
304 | +-------+-----+-----+-------+----+-------------+ | |
305 | 31 25 20 15 12 7 0 | |
306 | @end verbatim | |
307 | ||
308 | @item R type with 4 register operands: .insn r opcode, func3, func2, rd, rs1, rs2, rs3 | |
309 | @verbatim | |
310 | +-----+-------+-----+-----+-------+----+-------------+ | |
311 | | rs3 | func2 | rs2 | rs1 | func3 | rd | opcode | | |
312 | +-----+-------+-----+-----+-------+----+-------------+ | |
313 | 31 27 25 20 15 12 7 0 | |
314 | @end verbatim | |
315 | ||
316 | @item I type: .insn i opcode, func3, rd, rs1, simm12 | |
317 | @verbatim | |
318 | +-------------+-----+-------+----+-------------+ | |
319 | | simm12 | rs1 | func3 | rd | opcode | | |
320 | +-------------+-----+-------+----+-------------+ | |
321 | 31 20 15 12 7 0 | |
322 | @end verbatim | |
323 | ||
324 | @item S type: .insn s opcode, func3, rd, rs1, simm12 | |
325 | @verbatim | |
326 | +--------------+-----+-----+-------+-------------+-------------+ | |
327 | | simm12[11:5] | rs2 | rs1 | func3 | simm12[4:0] | opcode | | |
328 | +--------------+-----+-----+-------+-------------+-------------+ | |
329 | 31 25 20 15 12 7 0 | |
330 | @end verbatim | |
331 | ||
332 | @item SB type: .insn sb opcode, func3, rd, rs1, symbol | |
333 | @itemx SB type: .insn sb opcode, func3, rd, simm12(rs1) | |
334 | @verbatim | |
335 | +--------------+-----+-----+-------+-------------+-------------+ | |
336 | | simm21[11:5] | rs2 | rs1 | func3 | simm12[4:0] | opcode | | |
337 | +--------------+-----+-----+-------+-------------+-------------+ | |
338 | 31 25 20 15 12 7 0 | |
339 | @end verbatim | |
340 | ||
341 | @item U type: .insn u opcode, rd, simm20 | |
342 | @verbatim | |
343 | +---------------------------+----+-------------+ | |
344 | | simm20 | rd | opcode | | |
345 | +---------------------------+----+-------------+ | |
346 | 31 12 7 0 | |
347 | @end verbatim | |
348 | ||
349 | @item UJ type: .insn uj opcode, rd, symbol | |
350 | @verbatim | |
351 | +------------+--------------+------------+---------------+----+-------------+ | |
352 | | simm20[20] | simm20[10:1] | simm20[11] | simm20[19:12] | rd | opcode | | |
353 | +------------+--------------+------------+---------------+----+-------------+ | |
354 | 31 30 21 20 12 7 0 | |
355 | @end verbatim | |
356 | ||
357 | @item CR type: .insn cr opcode2, func4, rd, rs1 | |
358 | @verbatim | |
359 | +---------+--------+-----+---------+ | |
360 | | func4 | rd/rs1 | rs2 | opcode2 | | |
361 | +---------+--------+-----+---------+ | |
362 | 15 12 7 2 0 | |
363 | @end verbatim | |
364 | ||
365 | @item CI type: .insn ci opcode2, func3, rd, simm6 | |
366 | @verbatim | |
367 | +---------+-----+--------+-----+---------+ | |
368 | | func3 | imm | rd/rs1 | imm | opcode2 | | |
369 | +---------+-----+--------+-----+---------+ | |
370 | 15 13 12 7 2 0 | |
371 | @end verbatim | |
372 | ||
373 | @item CIW type: .insn ciw opcode2, func3, rd, uimm8 | |
374 | @verbatim | |
375 | +---------+--------------+-----+---------+ | |
376 | | func3 | imm | rd' | opcode2 | | |
377 | +---------+--------------+-----+---------+ | |
378 | 15 13 7 2 0 | |
379 | @end verbatim | |
380 | ||
381 | @item CB type: .insn cb opcode2, func3, rs1, symbol | |
382 | @verbatim | |
383 | +---------+--------+------+--------+---------+ | |
384 | | func3 | offset | rs1' | offset | opcode2 | | |
385 | +---------+--------+------+--------+---------+ | |
386 | 15 13 10 7 2 0 | |
387 | @end verbatim | |
388 | ||
389 | @item CJ type: .insn cj opcode2, symbol | |
390 | @verbatim | |
391 | +---------+--------------------+---------+ | |
392 | | func3 | jump target | opcode2 | | |
393 | +---------+--------------------+---------+ | |
394 | 15 13 7 2 0 | |
395 | @end verbatim | |
396 | ||
397 | ||
398 | @end table | |
399 | ||
400 | For the complete list of all instruction format variants see | |
401 | The RISC-V Instruction Set Manual Volume I: User-Level ISA. |