Commit | Line | Data |
---|---|---|
aa820537 AM |
1 | @c Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008 |
2 | @c Free Software Foundation, Inc. | |
e0001a05 NC |
3 | @c This is part of the GAS manual. |
4 | @c For copying conditions, see the file as.texinfo. | |
5 | @c | |
6 | @ifset GENERIC | |
7 | @page | |
8 | @node Xtensa-Dependent | |
9 | @chapter Xtensa Dependent Features | |
10 | @end ifset | |
11 | @ifclear GENERIC | |
12 | @node Machine Dependencies | |
13 | @chapter Xtensa Dependent Features | |
14 | @end ifclear | |
15 | ||
16 | @cindex Xtensa architecture | |
17 | This chapter covers features of the @sc{gnu} assembler that are specific | |
18 | to the Xtensa architecture. For details about the Xtensa instruction | |
19 | set, please consult the @cite{Xtensa Instruction Set Architecture (ISA) | |
20 | Reference Manual}. | |
21 | ||
22 | @menu | |
23 | * Xtensa Options:: Command-line Options. | |
24 | * Xtensa Syntax:: Assembler Syntax for Xtensa Processors. | |
25 | * Xtensa Optimizations:: Assembler Optimizations. | |
26 | * Xtensa Relaxation:: Other Automatic Transformations. | |
27 | * Xtensa Directives:: Directives for Xtensa Processors. | |
28 | @end menu | |
29 | ||
30 | @node Xtensa Options | |
31 | @section Command Line Options | |
32 | ||
33 | The Xtensa version of the @sc{gnu} assembler supports these | |
34 | special options: | |
35 | ||
36 | @table @code | |
e0001a05 NC |
37 | @item --text-section-literals | --no-text-section-literals |
38 | @kindex --text-section-literals | |
39 | @kindex --no-text-section-literals | |
40 | Control the treatment of literal pools. The default is | |
74869ac7 BW |
41 | @samp{--no-@-text-@-section-@-literals}, which places literals in |
42 | separate sections in the output file. This allows the literal pool to be | |
43cd72b9 | 43 | placed in a data RAM/ROM. With @samp{--text-@-section-@-literals}, the |
e0001a05 NC |
44 | literals are interspersed in the text section in order to keep them as |
45 | close as possible to their references. This may be necessary for large | |
43cd72b9 BW |
46 | assembly files, where the literals would otherwise be out of range of the |
47 | @code{L32R} instructions in the text section. These options only affect | |
48 | literals referenced via PC-relative @code{L32R} instructions; literals | |
49 | for absolute mode @code{L32R} instructions are handled separately. | |
74869ac7 | 50 | @xref{Literal Directive, ,literal}. |
43cd72b9 BW |
51 | |
52 | @item --absolute-literals | --no-absolute-literals | |
53 | @kindex --absolute-literals | |
54 | @kindex --no-absolute-literals | |
55 | Indicate to the assembler whether @code{L32R} instructions use absolute | |
56 | or PC-relative addressing. If the processor includes the absolute | |
57 | addressing option, the default is to use absolute @code{L32R} | |
58 | relocations. Otherwise, only the PC-relative @code{L32R} relocations | |
40e7b7b9 | 59 | can be used. |
e0001a05 NC |
60 | |
61 | @item --target-align | --no-target-align | |
62 | @kindex --target-align | |
63 | @kindex --no-target-align | |
64 | Enable or disable automatic alignment to reduce branch penalties at some | |
65 | expense in code size. @xref{Xtensa Automatic Alignment, ,Automatic | |
66 | Instruction Alignment}. This optimization is enabled by default. Note | |
67 | that the assembler will always align instructions like @code{LOOP} that | |
68 | have fixed alignment requirements. | |
69 | ||
70 | @item --longcalls | --no-longcalls | |
71 | @kindex --longcalls | |
72 | @kindex --no-longcalls | |
73 | Enable or disable transformation of call instructions to allow calls | |
74 | across a greater range of addresses. @xref{Xtensa Call Relaxation, | |
75 | ,Function Call Relaxation}. This option should be used when call | |
43cd72b9 BW |
76 | targets can potentially be out of range. It may degrade both code size |
77 | and performance, but the linker can generally optimize away the | |
78 | unnecessary overhead when a call ends up within range. The default is | |
79 | @samp{--no-@-longcalls}. | |
80 | ||
81 | @item --transform | --no-transform | |
82 | @kindex --transform | |
83 | @kindex --no-transform | |
84 | Enable or disable all assembler transformations of Xtensa instructions, | |
85 | including both relaxation and optimization. The default is | |
86 | @samp{--transform}; @samp{--no-transform} should only be used in the | |
87 | rare cases when the instructions must be exactly as specified in the | |
88 | assembly source. Using @samp{--no-transform} causes out of range | |
89 | instruction operands to be errors. | |
9456465c BW |
90 | |
91 | @item --rename-section @var{oldname}=@var{newname} | |
92 | @kindex --rename-section | |
93 | Rename the @var{oldname} section to @var{newname}. This option can be used | |
94 | multiple times to rename multiple sections. | |
e0001a05 NC |
95 | @end table |
96 | ||
97 | @node Xtensa Syntax | |
98 | @section Assembler Syntax | |
99 | @cindex syntax, Xtensa assembler | |
100 | @cindex Xtensa assembler syntax | |
43cd72b9 | 101 | @cindex FLIX syntax |
e0001a05 NC |
102 | |
103 | Block comments are delimited by @samp{/*} and @samp{*/}. End of line | |
104 | comments may be introduced with either @samp{#} or @samp{//}. | |
105 | ||
106 | Instructions consist of a leading opcode or macro name followed by | |
107 | whitespace and an optional comma-separated list of operands: | |
108 | ||
109 | @smallexample | |
43cd72b9 | 110 | @var{opcode} [@var{operand}, @dots{}] |
e0001a05 NC |
111 | @end smallexample |
112 | ||
113 | Instructions must be separated by a newline or semicolon. | |
114 | ||
43cd72b9 BW |
115 | FLIX instructions, which bundle multiple opcodes together in a single |
116 | instruction, are specified by enclosing the bundled opcodes inside | |
117 | braces: | |
118 | ||
119 | @smallexample | |
34135039 | 120 | @group |
43cd72b9 BW |
121 | @{ |
122 | [@var{format}] | |
123 | @var{opcode0} [@var{operands}] | |
34135039 | 124 | @end group |
43cd72b9 | 125 | @var{opcode1} [@var{operands}] |
34135039 | 126 | @group |
43cd72b9 BW |
127 | @var{opcode2} [@var{operands}] |
128 | @dots{} | |
129 | @} | |
34135039 | 130 | @end group |
43cd72b9 BW |
131 | @end smallexample |
132 | ||
133 | The opcodes in a FLIX instruction are listed in the same order as the | |
134 | corresponding instruction slots in the TIE format declaration. | |
135 | Directives and labels are not allowed inside the braces of a FLIX | |
136 | instruction. A particular TIE format name can optionally be specified | |
137 | immediately after the opening brace, but this is usually unnecessary. | |
138 | The assembler will automatically search for a format that can encode the | |
139 | specified opcodes, so the format name need only be specified in rare | |
140 | cases where there is more than one applicable format and where it | |
141 | matters which of those formats is used. A FLIX instruction can also be | |
142 | specified on a single line by separating the opcodes with semicolons: | |
143 | ||
144 | @smallexample | |
145 | @{ [@var{format};] @var{opcode0} [@var{operands}]; @var{opcode1} [@var{operands}]; @var{opcode2} [@var{operands}]; @dots{} @} | |
146 | @end smallexample | |
147 | ||
cec28c98 BW |
148 | If an opcode can only be encoded in a FLIX instruction but is not |
149 | specified as part of a FLIX bundle, the assembler will choose the | |
150 | smallest format where the opcode can be encoded and | |
151 | will fill unused instruction slots with no-ops. | |
43cd72b9 | 152 | |
e0001a05 NC |
153 | @menu |
154 | * Xtensa Opcodes:: Opcode Naming Conventions. | |
155 | * Xtensa Registers:: Register Naming. | |
156 | @end menu | |
157 | ||
158 | @node Xtensa Opcodes | |
159 | @subsection Opcode Names | |
160 | @cindex Xtensa opcode names | |
43cd72b9 | 161 | @cindex opcode names, Xtensa |
e0001a05 NC |
162 | |
163 | See the @cite{Xtensa Instruction Set Architecture (ISA) Reference | |
164 | Manual} for a complete list of opcodes and descriptions of their | |
165 | semantics. | |
166 | ||
e0001a05 | 167 | @cindex _ opcode prefix |
43cd72b9 BW |
168 | If an opcode name is prefixed with an underscore character (@samp{_}), |
169 | @command{@value{AS}} will not transform that instruction in any way. The | |
170 | underscore prefix disables both optimization (@pxref{Xtensa | |
171 | Optimizations, ,Xtensa Optimizations}) and relaxation (@pxref{Xtensa | |
172 | Relaxation, ,Xtensa Relaxation}) for that particular instruction. Only | |
173 | use the underscore prefix when it is essential to select the exact | |
174 | opcode produced by the assembler. Using this feature unnecessarily | |
175 | makes the code less efficient by disabling assembler optimization and | |
176 | less flexible by disabling relaxation. | |
e0001a05 NC |
177 | |
178 | Note that this special handling of underscore prefixes only applies to | |
179 | Xtensa opcodes, not to either built-in macros or user-defined macros. | |
43cd72b9 | 180 | When an underscore prefix is used with a macro (e.g., @code{_MOV}), it |
e0001a05 NC |
181 | refers to a different macro. The assembler generally provides built-in |
182 | macros both with and without the underscore prefix, where the underscore | |
183 | versions behave as if the underscore carries through to the instructions | |
43cd72b9 | 184 | in the macros. For example, @code{_MOV} may expand to @code{_MOV.N}@. |
e0001a05 NC |
185 | |
186 | The underscore prefix only applies to individual instructions, not to | |
187 | series of instructions. For example, if a series of instructions have | |
188 | underscore prefixes, the assembler will not transform the individual | |
189 | instructions, but it may insert other instructions between them (e.g., | |
190 | to align a @code{LOOP} instruction). To prevent the assembler from | |
191 | modifying a series of instructions as a whole, use the | |
43cd72b9 | 192 | @code{no-transform} directive. @xref{Transform Directive, ,transform}. |
e0001a05 NC |
193 | |
194 | @node Xtensa Registers | |
195 | @subsection Register Names | |
196 | @cindex Xtensa register names | |
197 | @cindex register names, Xtensa | |
198 | @cindex sp register | |
199 | ||
43cd72b9 BW |
200 | The assembly syntax for a register file entry is the ``short'' name for |
201 | a TIE register file followed by the index into that register file. For | |
202 | example, the general-purpose @code{AR} register file has a short name of | |
203 | @code{a}, so these registers are named @code{a0}@dots{}@code{a15}. | |
204 | As a special feature, @code{sp} is also supported as a synonym for | |
205 | @code{a1}. Additional registers may be added by processor configuration | |
206 | options and by designer-defined TIE extensions. An initial @samp{$} | |
207 | character is optional in all register names. | |
e0001a05 NC |
208 | |
209 | @node Xtensa Optimizations | |
210 | @section Xtensa Optimizations | |
211 | @cindex optimizations | |
212 | ||
43cd72b9 | 213 | The optimizations currently supported by @command{@value{AS}} are |
e0001a05 NC |
214 | generation of density instructions where appropriate and automatic |
215 | branch target alignment. | |
216 | ||
217 | @menu | |
218 | * Density Instructions:: Using Density Instructions. | |
219 | * Xtensa Automatic Alignment:: Automatic Instruction Alignment. | |
220 | @end menu | |
221 | ||
222 | @node Density Instructions | |
223 | @subsection Using Density Instructions | |
224 | @cindex density instructions | |
225 | ||
226 | The Xtensa instruction set has a code density option that provides | |
227 | 16-bit versions of some of the most commonly used opcodes. Use of these | |
228 | opcodes can significantly reduce code size. When possible, the | |
43cd72b9 | 229 | assembler automatically translates instructions from the core |
e0001a05 | 230 | Xtensa instruction set into equivalent instructions from the Xtensa code |
43cd72b9 BW |
231 | density option. This translation can be disabled by using underscore |
232 | prefixes (@pxref{Xtensa Opcodes, ,Opcode Names}), by using the | |
233 | @samp{--no-transform} command-line option (@pxref{Xtensa Options, ,Command | |
234 | Line Options}), or by using the @code{no-transform} directive | |
235 | (@pxref{Transform Directive, ,transform}). | |
e0001a05 | 236 | |
60493797 | 237 | It is a good idea @emph{not} to use the density instructions directly. |
e0001a05 | 238 | The assembler will automatically select dense instructions where |
43cd72b9 BW |
239 | possible. If you later need to use an Xtensa processor without the code |
240 | density option, the same assembly code will then work without modification. | |
e0001a05 NC |
241 | |
242 | @node Xtensa Automatic Alignment | |
243 | @subsection Automatic Instruction Alignment | |
244 | @cindex alignment of @code{LOOP} instructions | |
e0001a05 NC |
245 | @cindex alignment of branch targets |
246 | @cindex @code{LOOP} instructions, alignment | |
e0001a05 NC |
247 | @cindex branch target alignment |
248 | ||
249 | The Xtensa assembler will automatically align certain instructions, both | |
250 | to optimize performance and to satisfy architectural requirements. | |
251 | ||
43cd72b9 BW |
252 | As an optimization to improve performance, the assembler attempts to |
253 | align branch targets so they do not cross instruction fetch boundaries. | |
254 | (Xtensa processors can be configured with either 32-bit or 64-bit | |
255 | instruction fetch widths.) An | |
256 | instruction immediately following a call is treated as a branch target | |
257 | in this context, because it will be the target of a return from the | |
258 | call. This alignment has the potential to reduce branch penalties at | |
cec28c98 | 259 | some expense in code size. |
43cd72b9 BW |
260 | This optimization is enabled by default. You can disable it with the |
261 | @samp{--no-target-@-align} command-line option (@pxref{Xtensa Options, | |
262 | ,Command Line Options}). | |
263 | ||
264 | The target alignment optimization is done without adding instructions | |
265 | that could increase the execution time of the program. If there are | |
266 | density instructions in the code preceding a target, the assembler can | |
267 | change the target alignment by widening some of those instructions to | |
268 | the equivalent 24-bit instructions. Extra bytes of padding can be | |
269 | inserted immediately following unconditional jump and return | |
270 | instructions. | |
271 | This approach is usually successful in aligning many, but not all, | |
272 | branch targets. | |
273 | ||
274 | The @code{LOOP} family of instructions must be aligned such that the | |
275 | first instruction in the loop body does not cross an instruction fetch | |
276 | boundary (e.g., with a 32-bit fetch width, a @code{LOOP} instruction | |
277 | must be on either a 1 or 2 mod 4 byte boundary). The assembler knows | |
278 | about this restriction and inserts the minimal number of 2 or 3 byte | |
279 | no-op instructions to satisfy it. When no-op instructions are added, | |
280 | any label immediately preceding the original loop will be moved in order | |
281 | to refer to the loop instruction, not the newly generated no-op | |
282 | instruction. To preserve binary compatibility across processors with | |
283 | different fetch widths, the assembler conservatively assumes a 32-bit | |
284 | fetch width when aligning @code{LOOP} instructions (except if the first | |
285 | instruction in the loop is a 64-bit instruction). | |
e0001a05 | 286 | |
4c8d1ad4 BW |
287 | Previous versions of the assembler automatically aligned @code{ENTRY} |
288 | instructions to 4-byte boundaries, but that alignment is now the | |
289 | programmer's responsibility. | |
e0001a05 NC |
290 | |
291 | @node Xtensa Relaxation | |
292 | @section Xtensa Relaxation | |
293 | @cindex relaxation | |
294 | ||
295 | When an instruction operand is outside the range allowed for that | |
43cd72b9 | 296 | particular instruction field, @command{@value{AS}} can transform the code |
e0001a05 NC |
297 | to use a functionally-equivalent instruction or sequence of |
298 | instructions. This process is known as @dfn{relaxation}. This is | |
299 | typically done for branch instructions because the distance of the | |
300 | branch targets is not known until assembly-time. The Xtensa assembler | |
301 | offers branch relaxation and also extends this concept to function | |
302 | calls, @code{MOVI} instructions and other instructions with immediate | |
303 | fields. | |
304 | ||
305 | @menu | |
306 | * Xtensa Branch Relaxation:: Relaxation of Branches. | |
307 | * Xtensa Call Relaxation:: Relaxation of Function Calls. | |
308 | * Xtensa Immediate Relaxation:: Relaxation of other Immediate Fields. | |
309 | @end menu | |
310 | ||
311 | @node Xtensa Branch Relaxation | |
312 | @subsection Conditional Branch Relaxation | |
313 | @cindex relaxation of branch instructions | |
314 | @cindex branch instructions, relaxation | |
315 | ||
316 | When the target of a branch is too far away from the branch itself, | |
317 | i.e., when the offset from the branch to the target is too large to fit | |
318 | in the immediate field of the branch instruction, it may be necessary to | |
319 | replace the branch with a branch around a jump. For example, | |
320 | ||
321 | @smallexample | |
322 | beqz a2, L | |
323 | @end smallexample | |
324 | ||
325 | may result in: | |
326 | ||
327 | @smallexample | |
34135039 | 328 | @group |
e0001a05 NC |
329 | bnez.n a2, M |
330 | j L | |
331 | M: | |
34135039 | 332 | @end group |
e0001a05 NC |
333 | @end smallexample |
334 | ||
335 | (The @code{BNEZ.N} instruction would be used in this example only if the | |
336 | density option is available. Otherwise, @code{BNEZ} would be used.) | |
337 | ||
43cd72b9 BW |
338 | This relaxation works well because the unconditional jump instruction |
339 | has a much larger offset range than the various conditional branches. | |
340 | However, an error will occur if a branch target is beyond the range of a | |
341 | jump instruction. @command{@value{AS}} cannot relax unconditional jumps. | |
342 | Similarly, an error will occur if the original input contains an | |
343 | unconditional jump to a target that is out of range. | |
344 | ||
345 | Branch relaxation is enabled by default. It can be disabled by using | |
346 | underscore prefixes (@pxref{Xtensa Opcodes, ,Opcode Names}), the | |
347 | @samp{--no-transform} command-line option (@pxref{Xtensa Options, | |
348 | ,Command Line Options}), or the @code{no-transform} directive | |
349 | (@pxref{Transform Directive, ,transform}). | |
350 | ||
e0001a05 NC |
351 | @node Xtensa Call Relaxation |
352 | @subsection Function Call Relaxation | |
353 | @cindex relaxation of call instructions | |
354 | @cindex call instructions, relaxation | |
355 | ||
356 | Function calls may require relaxation because the Xtensa immediate call | |
357 | instructions (@code{CALL0}, @code{CALL4}, @code{CALL8} and | |
358 | @code{CALL12}) provide a PC-relative offset of only 512 Kbytes in either | |
359 | direction. For larger programs, it may be necessary to use indirect | |
360 | calls (@code{CALLX0}, @code{CALLX4}, @code{CALLX8} and @code{CALLX12}) | |
361 | where the target address is specified in a register. The Xtensa | |
362 | assembler can automatically relax immediate call instructions into | |
363 | indirect call instructions. This relaxation is done by loading the | |
364 | address of the called function into the callee's return address register | |
365 | and then using a @code{CALLX} instruction. So, for example: | |
366 | ||
367 | @smallexample | |
368 | call8 func | |
369 | @end smallexample | |
370 | ||
371 | might be relaxed to: | |
372 | ||
373 | @smallexample | |
34135039 | 374 | @group |
e0001a05 NC |
375 | .literal .L1, func |
376 | l32r a8, .L1 | |
377 | callx8 a8 | |
34135039 | 378 | @end group |
e0001a05 NC |
379 | @end smallexample |
380 | ||
381 | Because the addresses of targets of function calls are not generally | |
382 | known until link-time, the assembler must assume the worst and relax all | |
383 | the calls to functions in other source files, not just those that really | |
384 | will be out of range. The linker can recognize calls that were | |
43cd72b9 BW |
385 | unnecessarily relaxed, and it will remove the overhead introduced by the |
386 | assembler for those cases where direct calls are sufficient. | |
e0001a05 | 387 | |
43cd72b9 BW |
388 | Call relaxation is disabled by default because it can have a negative |
389 | effect on both code size and performance, although the linker can | |
390 | usually eliminate the unnecessary overhead. If a program is too large | |
391 | and some of the calls are out of range, function call relaxation can be | |
392 | enabled using the @samp{--longcalls} command-line option or the | |
393 | @code{longcalls} directive (@pxref{Longcalls Directive, ,longcalls}). | |
e0001a05 NC |
394 | |
395 | @node Xtensa Immediate Relaxation | |
396 | @subsection Other Immediate Field Relaxation | |
397 | @cindex immediate fields, relaxation | |
398 | @cindex relaxation of immediate fields | |
399 | ||
43cd72b9 BW |
400 | The assembler normally performs the following other relaxations. They |
401 | can be disabled by using underscore prefixes (@pxref{Xtensa Opcodes, | |
402 | ,Opcode Names}), the @samp{--no-transform} command-line option | |
403 | (@pxref{Xtensa Options, ,Command Line Options}), or the | |
404 | @code{no-transform} directive (@pxref{Transform Directive, ,transform}). | |
405 | ||
e0001a05 NC |
406 | @cindex @code{MOVI} instructions, relaxation |
407 | @cindex relaxation of @code{MOVI} instructions | |
408 | The @code{MOVI} machine instruction can only materialize values in the | |
409 | range from -2048 to 2047. Values outside this range are best | |
60493797 | 410 | materialized with @code{L32R} instructions. Thus: |
e0001a05 NC |
411 | |
412 | @smallexample | |
413 | movi a0, 100000 | |
414 | @end smallexample | |
415 | ||
416 | is assembled into the following machine code: | |
417 | ||
418 | @smallexample | |
34135039 | 419 | @group |
e0001a05 NC |
420 | .literal .L1, 100000 |
421 | l32r a0, .L1 | |
34135039 | 422 | @end group |
e0001a05 NC |
423 | @end smallexample |
424 | ||
425 | @cindex @code{L8UI} instructions, relaxation | |
426 | @cindex @code{L16SI} instructions, relaxation | |
427 | @cindex @code{L16UI} instructions, relaxation | |
428 | @cindex @code{L32I} instructions, relaxation | |
429 | @cindex relaxation of @code{L8UI} instructions | |
430 | @cindex relaxation of @code{L16SI} instructions | |
431 | @cindex relaxation of @code{L16UI} instructions | |
432 | @cindex relaxation of @code{L32I} instructions | |
433 | The @code{L8UI} machine instruction can only be used with immediate | |
434 | offsets in the range from 0 to 255. The @code{L16SI} and @code{L16UI} | |
435 | machine instructions can only be used with offsets from 0 to 510. The | |
436 | @code{L32I} machine instruction can only be used with offsets from 0 to | |
b45619c0 | 437 | 1020. A load offset outside these ranges can be materialized with |
e0001a05 NC |
438 | an @code{L32R} instruction if the destination register of the load |
439 | is different than the source address register. For example: | |
440 | ||
441 | @smallexample | |
442 | l32i a1, a0, 2040 | |
443 | @end smallexample | |
444 | ||
445 | is translated to: | |
446 | ||
447 | @smallexample | |
34135039 | 448 | @group |
e0001a05 NC |
449 | .literal .L1, 2040 |
450 | l32r a1, .L1 | |
34135039 BW |
451 | @end group |
452 | @group | |
e055a931 | 453 | add a1, a0, a1 |
e0001a05 | 454 | l32i a1, a1, 0 |
34135039 | 455 | @end group |
e0001a05 NC |
456 | @end smallexample |
457 | ||
458 | @noindent | |
459 | If the load destination and source address register are the same, an | |
460 | out-of-range offset causes an error. | |
461 | ||
462 | @cindex @code{ADDI} instructions, relaxation | |
463 | @cindex relaxation of @code{ADDI} instructions | |
464 | The Xtensa @code{ADDI} instruction only allows immediate operands in the | |
465 | range from -128 to 127. There are a number of alternate instruction | |
43cd72b9 | 466 | sequences for the @code{ADDI} operation. First, if the |
e0001a05 NC |
467 | immediate is 0, the @code{ADDI} will be turned into a @code{MOV.N} |
468 | instruction (or the equivalent @code{OR} instruction if the code density | |
469 | option is not available). If the @code{ADDI} immediate is outside of | |
470 | the range -128 to 127, but inside the range -32896 to 32639, an | |
471 | @code{ADDMI} instruction or @code{ADDMI}/@code{ADDI} sequence will be | |
472 | used. Finally, if the immediate is outside of this range and a free | |
473 | register is available, an @code{L32R}/@code{ADD} sequence will be used | |
474 | with a literal allocated from the literal pool. | |
475 | ||
476 | For example: | |
477 | ||
478 | @smallexample | |
34135039 | 479 | @group |
e0001a05 NC |
480 | addi a5, a6, 0 |
481 | addi a5, a6, 512 | |
34135039 BW |
482 | @end group |
483 | @group | |
e0001a05 NC |
484 | addi a5, a6, 513 |
485 | addi a5, a6, 50000 | |
34135039 | 486 | @end group |
e0001a05 NC |
487 | @end smallexample |
488 | ||
489 | is assembled into the following: | |
490 | ||
491 | @smallexample | |
34135039 | 492 | @group |
e0001a05 NC |
493 | .literal .L1, 50000 |
494 | mov.n a5, a6 | |
34135039 | 495 | @end group |
e0001a05 NC |
496 | addmi a5, a6, 0x200 |
497 | addmi a5, a6, 0x200 | |
498 | addi a5, a5, 1 | |
34135039 | 499 | @group |
e0001a05 NC |
500 | l32r a5, .L1 |
501 | add a5, a6, a5 | |
34135039 | 502 | @end group |
e0001a05 NC |
503 | @end smallexample |
504 | ||
505 | @node Xtensa Directives | |
506 | @section Directives | |
507 | @cindex Xtensa directives | |
508 | @cindex directives, Xtensa | |
509 | ||
b45619c0 | 510 | The Xtensa assembler supports a region-based directive syntax: |
e0001a05 NC |
511 | |
512 | @smallexample | |
34135039 | 513 | @group |
e0001a05 NC |
514 | .begin @var{directive} [@var{options}] |
515 | @dots{} | |
516 | .end @var{directive} | |
34135039 | 517 | @end group |
e0001a05 NC |
518 | @end smallexample |
519 | ||
520 | All the Xtensa-specific directives that apply to a region of code use | |
521 | this syntax. | |
522 | ||
523 | The directive applies to code between the @code{.begin} and the | |
524 | @code{.end}. The state of the option after the @code{.end} reverts to | |
525 | what it was before the @code{.begin}. | |
526 | A nested @code{.begin}/@code{.end} region can further | |
527 | change the state of the directive without having to be aware of its | |
528 | outer state. For example, consider: | |
529 | ||
530 | @smallexample | |
34135039 | 531 | @group |
43cd72b9 | 532 | .begin no-transform |
e0001a05 | 533 | L: add a0, a1, a2 |
34135039 | 534 | @end group |
43cd72b9 | 535 | .begin transform |
e0001a05 | 536 | M: add a0, a1, a2 |
43cd72b9 | 537 | .end transform |
34135039 | 538 | @group |
e0001a05 | 539 | N: add a0, a1, a2 |
43cd72b9 | 540 | .end no-transform |
34135039 | 541 | @end group |
e0001a05 NC |
542 | @end smallexample |
543 | ||
43cd72b9 BW |
544 | The @code{ADD} opcodes at @code{L} and @code{N} in the outer |
545 | @code{no-transform} region both result in @code{ADD} machine instructions, | |
546 | but the assembler selects an @code{ADD.N} instruction for the | |
547 | @code{ADD} at @code{M} in the inner @code{transform} region. | |
e0001a05 NC |
548 | |
549 | The advantage of this style is that it works well inside macros which can | |
550 | preserve the context of their callers. | |
551 | ||
e0001a05 NC |
552 | The following directives are available: |
553 | @menu | |
43cd72b9 | 554 | * Schedule Directive:: Enable instruction scheduling. |
e0001a05 | 555 | * Longcalls Directive:: Use Indirect Calls for Greater Range. |
43cd72b9 | 556 | * Transform Directive:: Disable All Assembler Transformations. |
e0001a05 NC |
557 | * Literal Directive:: Intermix Literals with Instructions. |
558 | * Literal Position Directive:: Specify Inline Literal Pool Locations. | |
559 | * Literal Prefix Directive:: Specify Literal Section Name Prefix. | |
43cd72b9 | 560 | * Absolute Literals Directive:: Control PC-Relative vs. Absolute Literals. |
e0001a05 NC |
561 | @end menu |
562 | ||
43cd72b9 BW |
563 | @node Schedule Directive |
564 | @subsection schedule | |
565 | @cindex @code{schedule} directive | |
566 | @cindex @code{no-schedule} directive | |
e0001a05 | 567 | |
43cd72b9 BW |
568 | The @code{schedule} directive is recognized only for compatibility with |
569 | Tensilica's assembler. | |
e0001a05 NC |
570 | |
571 | @smallexample | |
34135039 | 572 | @group |
43cd72b9 BW |
573 | .begin [no-]schedule |
574 | .end [no-]schedule | |
34135039 | 575 | @end group |
e0001a05 NC |
576 | @end smallexample |
577 | ||
43cd72b9 | 578 | This directive is ignored and has no effect on @command{@value{AS}}. |
e0001a05 NC |
579 | |
580 | @node Longcalls Directive | |
581 | @subsection longcalls | |
582 | @cindex @code{longcalls} directive | |
583 | @cindex @code{no-longcalls} directive | |
584 | ||
585 | The @code{longcalls} directive enables or disables function call | |
586 | relaxation. @xref{Xtensa Call Relaxation, ,Function Call Relaxation}. | |
587 | ||
588 | @smallexample | |
34135039 | 589 | @group |
e0001a05 NC |
590 | .begin [no-]longcalls |
591 | .end [no-]longcalls | |
34135039 | 592 | @end group |
e0001a05 NC |
593 | @end smallexample |
594 | ||
595 | Call relaxation is disabled by default unless the @samp{--longcalls} | |
43cd72b9 BW |
596 | command-line option is specified. The @code{longcalls} directive |
597 | overrides the default determined by the command-line options. | |
e0001a05 | 598 | |
43cd72b9 BW |
599 | @node Transform Directive |
600 | @subsection transform | |
601 | @cindex @code{transform} directive | |
602 | @cindex @code{no-transform} directive | |
e0001a05 NC |
603 | |
604 | This directive enables or disables all assembler transformation, | |
605 | including relaxation (@pxref{Xtensa Relaxation, ,Xtensa Relaxation}) and | |
606 | optimization (@pxref{Xtensa Optimizations, ,Xtensa Optimizations}). | |
607 | ||
608 | @smallexample | |
34135039 | 609 | @group |
43cd72b9 BW |
610 | .begin [no-]transform |
611 | .end [no-]transform | |
34135039 | 612 | @end group |
e0001a05 NC |
613 | @end smallexample |
614 | ||
43cd72b9 BW |
615 | Transformations are enabled by default unless the @samp{--no-transform} |
616 | option is used. The @code{transform} directive overrides the default | |
617 | determined by the command-line options. An underscore opcode prefix, | |
618 | disabling transformation of that opcode, always takes precedence over | |
619 | both directives and command-line flags. | |
e0001a05 NC |
620 | |
621 | @node Literal Directive | |
622 | @subsection literal | |
623 | @cindex @code{literal} directive | |
624 | ||
625 | The @code{.literal} directive is used to define literal pool data, i.e., | |
626 | read-only 32-bit data accessed via @code{L32R} instructions. | |
627 | ||
628 | @smallexample | |
629 | .literal @var{label}, @var{value}[, @var{value}@dots{}] | |
630 | @end smallexample | |
631 | ||
632 | This directive is similar to the standard @code{.word} directive, except | |
633 | that the actual location of the literal data is determined by the | |
634 | assembler and linker, not by the position of the @code{.literal} | |
635 | directive. Using this directive gives the assembler freedom to locate | |
636 | the literal data in the most appropriate place and possibly to combine | |
637 | identical literals. For example, the code: | |
638 | ||
639 | @smallexample | |
34135039 | 640 | @group |
e0001a05 NC |
641 | entry sp, 40 |
642 | .literal .L1, sym | |
643 | l32r a4, .L1 | |
34135039 | 644 | @end group |
e0001a05 NC |
645 | @end smallexample |
646 | ||
647 | can be used to load a pointer to the symbol @code{sym} into register | |
648 | @code{a4}. The value of @code{sym} will not be placed between the | |
649 | @code{ENTRY} and @code{L32R} instructions; instead, the assembler puts | |
650 | the data in a literal pool. | |
651 | ||
74869ac7 BW |
652 | Literal pools are placed by default in separate literal sections; |
653 | however, when using the @samp{--text-@-section-@-literals} | |
40e7b7b9 | 654 | option (@pxref{Xtensa Options, ,Command Line Options}), the literal |
74869ac7 BW |
655 | pools for PC-relative mode @code{L32R} instructions |
656 | are placed in the current section.@footnote{Literals for the | |
657 | @code{.init} and @code{.fini} sections are always placed in separate | |
658 | sections, even when @samp{--text-@-section-@-literals} is enabled.} | |
659 | These text section literal | |
40e7b7b9 BW |
660 | pools are created automatically before @code{ENTRY} instructions and |
661 | manually after @samp{.literal_position} directives (@pxref{Literal | |
662 | Position Directive, ,literal_position}). If there are no preceding | |
663 | @code{ENTRY} instructions, explicit @code{.literal_position} directives | |
664 | must be used to place the text section literal pools; otherwise, | |
43cd72b9 | 665 | @command{@value{AS}} will report an error. |
e0001a05 | 666 | |
74869ac7 BW |
667 | When literals are placed in separate sections, the literal section names |
668 | are derived from the names of the sections where the literals are | |
669 | defined. The base literal section names are @code{.literal} for | |
670 | PC-relative mode @code{L32R} instructions and @code{.lit4} for absolute | |
671 | mode @code{L32R} instructions (@pxref{Absolute Literals Directive, | |
672 | ,absolute-literals}). These base names are used for literals defined in | |
673 | the default @code{.text} section. For literals defined in other | |
674 | sections or within the scope of a @code{literal_prefix} directive | |
675 | (@pxref{Literal Prefix Directive, ,literal_prefix}), the following rules | |
676 | determine the literal section name: | |
677 | ||
678 | @enumerate | |
679 | @item | |
680 | If the current section is a member of a section group, the literal | |
681 | section name includes the group name as a suffix to the base | |
682 | @code{.literal} or @code{.lit4} name, with a period to separate the base | |
683 | name and group name. The literal section is also made a member of the | |
684 | group. | |
685 | ||
686 | @item | |
687 | If the current section name (or @code{literal_prefix} value) begins with | |
688 | ``@code{.gnu.linkonce.@var{kind}.}'', the literal section name is formed | |
689 | by replacing ``@code{.@var{kind}}'' with the base @code{.literal} or | |
690 | @code{.lit4} name. For example, for literals defined in a section named | |
691 | @code{.gnu.linkonce.t.func}, the literal section will be | |
692 | @code{.gnu.linkonce.literal.func} or @code{.gnu.linkonce.lit4.func}. | |
693 | ||
694 | @item | |
695 | If the current section name (or @code{literal_prefix} value) ends with | |
696 | @code{.text}, the literal section name is formed by replacing that | |
697 | suffix with the base @code{.literal} or @code{.lit4} name. For example, | |
698 | for literals defined in a section named @code{.iram0.text}, the literal | |
699 | section will be @code{.iram0.literal} or @code{.iram0.lit4}. | |
700 | ||
701 | @item | |
702 | If none of the preceding conditions apply, the literal section name is | |
703 | formed by adding the base @code{.literal} or @code{.lit4} name as a | |
704 | suffix to the current section name (or @code{literal_prefix} value). | |
705 | @end enumerate | |
706 | ||
e0001a05 NC |
707 | @node Literal Position Directive |
708 | @subsection literal_position | |
709 | @cindex @code{literal_position} directive | |
710 | ||
711 | When using @samp{--text-@-section-@-literals} to place literals inline | |
712 | in the section being assembled, the @code{.literal_position} directive | |
713 | can be used to mark a potential location for a literal pool. | |
714 | ||
715 | @smallexample | |
716 | .literal_position | |
717 | @end smallexample | |
718 | ||
719 | The @code{.literal_position} directive is ignored when the | |
43cd72b9 BW |
720 | @samp{--text-@-section-@-literals} option is not used or when |
721 | @code{L32R} instructions use the absolute addressing mode. | |
e0001a05 NC |
722 | |
723 | The assembler will automatically place text section literal pools | |
724 | before @code{ENTRY} instructions, so the @code{.literal_position} | |
725 | directive is only needed to specify some other location for a literal | |
726 | pool. You may need to add an explicit jump instruction to skip over an | |
727 | inline literal pool. | |
728 | ||
729 | For example, an interrupt vector does not begin with an @code{ENTRY} | |
730 | instruction so the assembler will be unable to automatically find a good | |
731 | place to put a literal pool. Moreover, the code for the interrupt | |
732 | vector must be at a specific starting address, so the literal pool | |
733 | cannot come before the start of the code. The literal pool for the | |
734 | vector must be explicitly positioned in the middle of the vector (before | |
43cd72b9 BW |
735 | any uses of the literals, due to the negative offsets used by |
736 | PC-relative @code{L32R} instructions). The @code{.literal_position} | |
e0001a05 NC |
737 | directive can be used to do this. In the following code, the literal |
738 | for @samp{M} will automatically be aligned correctly and is placed after | |
739 | the unconditional jump. | |
740 | ||
741 | @smallexample | |
34135039 | 742 | @group |
e0001a05 NC |
743 | .global M |
744 | code_start: | |
34135039 | 745 | @end group |
e0001a05 NC |
746 | j continue |
747 | .literal_position | |
748 | .align 4 | |
34135039 | 749 | @group |
e0001a05 NC |
750 | continue: |
751 | movi a4, M | |
34135039 | 752 | @end group |
e0001a05 NC |
753 | @end smallexample |
754 | ||
755 | @node Literal Prefix Directive | |
756 | @subsection literal_prefix | |
757 | @cindex @code{literal_prefix} directive | |
758 | ||
74869ac7 BW |
759 | The @code{literal_prefix} directive allows you to override the default |
760 | literal section names, which are derived from the names of the sections | |
761 | where the literals are defined. | |
e0001a05 NC |
762 | |
763 | @smallexample | |
34135039 | 764 | @group |
e0001a05 NC |
765 | .begin literal_prefix [@var{name}] |
766 | .end literal_prefix | |
34135039 | 767 | @end group |
e0001a05 NC |
768 | @end smallexample |
769 | ||
74869ac7 BW |
770 | For literals defined within the delimited region, the literal section |
771 | names are derived from the @var{name} argument instead of the name of | |
772 | the current section. The rules used to derive the literal section names | |
773 | do not change. @xref{Literal Directive, ,literal}. If the @var{name} | |
40e7b7b9 BW |
774 | argument is omitted, the literal sections revert to the defaults. This |
775 | directive has no effect when using the | |
776 | @samp{--text-@-section-@-literals} option (@pxref{Xtensa Options, | |
777 | ,Command Line Options}). | |
778 | ||
43cd72b9 BW |
779 | @node Absolute Literals Directive |
780 | @subsection absolute-literals | |
781 | @cindex @code{absolute-literals} directive | |
782 | @cindex @code{no-absolute-literals} directive | |
e0001a05 | 783 | |
43cd72b9 BW |
784 | The @code{absolute-@-literals} and @code{no-@-absolute-@-literals} |
785 | directives control the absolute vs.@: PC-relative mode for @code{L32R} | |
786 | instructions. These are relevant only for Xtensa configurations that | |
787 | include the absolute addressing option for @code{L32R} instructions. | |
e0001a05 NC |
788 | |
789 | @smallexample | |
34135039 | 790 | @group |
43cd72b9 BW |
791 | .begin [no-]absolute-literals |
792 | .end [no-]absolute-literals | |
34135039 | 793 | @end group |
e0001a05 NC |
794 | @end smallexample |
795 | ||
43cd72b9 BW |
796 | These directives do not change the @code{L32R} mode---they only cause |
797 | the assembler to emit the appropriate kind of relocation for @code{L32R} | |
798 | instructions and to place the literal values in the appropriate section. | |
799 | To change the @code{L32R} mode, the program must write the | |
800 | @code{LITBASE} special register. It is the programmer's responsibility | |
801 | to keep track of the mode and indicate to the assembler which mode is | |
802 | used in each region of code. | |
803 | ||
43cd72b9 BW |
804 | If the Xtensa configuration includes the absolute @code{L32R} addressing |
805 | option, the default is to assume absolute @code{L32R} addressing unless | |
806 | the @samp{--no-@-absolute-@-literals} command-line option is specified. | |
807 | Otherwise, the default is to assume PC-relative @code{L32R} addressing. | |
808 | The @code{absolute-@-literals} directive can then be used to override | |
809 | the default determined by the command-line options. | |
e0001a05 | 810 | |
e0001a05 NC |
811 | @c Local Variables: |
812 | @c fill-column: 72 | |
813 | @c End: |