1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Linux/PA-RISC Project (http://www.parisc-linux.org/)
4  *
5  * Floating-point emulation code
6  *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
7  */
8 /*
9  * BEGIN_DESC
10  *
11  *  File:
12  *	@(#)	pa/fp/decode_exc.c		$ Revision: $
13  *
14  *  Purpose:
15  *	<<please update with a synopsis of the functionality provided by this file>>
16  *
17  *  External Interfaces:
18  *	<<the following list was autogenerated, please review>>
19  *	decode_fpu(Fpu_register, trap_counts)
20  *
21  *  Internal Interfaces:
22  *	<<please update>>
23  *
24  *  Theory:
25  *	<<please update with a overview of the operation of this file>>
26  *
27  * END_DESC
28 */
29 
30 #include <linux/kernel.h>
31 #include "float.h"
32 #include "sgl_float.h"
33 #include "dbl_float.h"
34 #include "cnv_float.h"
35 /* #include "types.h" */
36 #include <asm/signal.h>
37 #include <asm/siginfo.h>
38 /* #include <machine/sys/mdep_private.h> */
39 
40 #undef Fpustatus_register
41 #define Fpustatus_register Fpu_register[0]
42 
43 /* General definitions */
44 #define DOESTRAP 1
45 #define NOTRAP 0
46 #define SIGNALCODE(signal, code) ((signal) << 24 | (code))
47 #define copropbit	1<<31-2	/* bit position 2 */
48 #define opclass		9	/* bits 21 & 22 */
49 #define fmtbits		11	/* bits 19 & 20 */
50 #define df		13	/* bits 17 & 18 */
51 #define twobits		3	/* mask low-order 2 bits */
52 #define fivebits	31	/* mask low-order 5 bits */
53 #define MAX_EXCP_REG	7	/* number of excpeption registers to check */
54 
55 /* Exception register definitions */
56 #define Excp_type(index) Exceptiontype(Fpu_register[index])
57 #define Excp_instr(index) Instructionfield(Fpu_register[index])
58 #define Clear_excp_register(index) Allexception(Fpu_register[index]) = 0
59 #define Excp_format() \
60 	(current_ir >> ((current_ir>>opclass & twobits) == 1 ? df : fmtbits) & twobits)
61 
62 /* Miscellaneous definitions */
63 #define Fpu_sgl(index) Fpu_register[index*2]
64 
65 #define Fpu_dblp1(index) Fpu_register[index*2]
66 #define Fpu_dblp2(index) Fpu_register[(index*2)+1]
67 
68 #define Fpu_quadp1(index) Fpu_register[index*2]
69 #define Fpu_quadp2(index) Fpu_register[(index*2)+1]
70 #define Fpu_quadp3(index) Fpu_register[(index*2)+2]
71 #define Fpu_quadp4(index) Fpu_register[(index*2)+3]
72 
73 /* Single precision floating-point definitions */
74 #ifndef Sgl_decrement
75 # define Sgl_decrement(sgl_value) Sall(sgl_value)--
76 #endif
77 
78 /* Double precision floating-point definitions */
79 #ifndef Dbl_decrement
80 # define Dbl_decrement(dbl_valuep1,dbl_valuep2) \
81     if ((Dallp2(dbl_valuep2)--) == 0) Dallp1(dbl_valuep1)--
82 #endif
83 
84 
85 #define update_trap_counts(Fpu_register, aflags, bflags, trap_counts) {	\
86 	aflags=(Fpu_register[0])>>27;	/* assumes zero fill. 32 bit */	\
87 	Fpu_register[0] |= bflags;					\
88 }
89 
90 u_int
91 decode_fpu(unsigned int Fpu_register[], unsigned int trap_counts[])
92 {
93     unsigned int current_ir, excp;
94     int target, exception_index = 1;
95     boolean inexact;
96     unsigned int aflags;
97     unsigned int bflags;
98     unsigned int excptype;
99 
100 
101     /* Keep stats on how many floating point exceptions (based on type)
102      * that happen.  Want to keep this overhead low, but still provide
103      * some information to the customer.  All exits from this routine
104      * need to restore Fpu_register[0]
105     */
106 
107     bflags=(Fpu_register[0] & 0xf8000000);
108     Fpu_register[0] &= 0x07ffffff;
109 
110     /* exception_index is used to index the exception register queue.  It
111      *   always points at the last register that contains a valid exception.  A
112      *   zero value implies no exceptions (also the initialized value).  Setting
113      *   the T-bit resets the exception_index to zero.
114      */
115 
116     /*
117      * Check for reserved-op exception.  A reserved-op exception does not
118      * set any exception registers nor does it set the T-bit.  If the T-bit
119      * is not set then a reserved-op exception occurred.
120      *
121      * At some point, we may want to report reserved op exceptions as
122      * illegal instructions.
123      */
124 
125     if (!Is_tbit_set()) {
126 	update_trap_counts(Fpu_register, aflags, bflags, trap_counts);
127 	return SIGNALCODE(SIGILL, ILL_COPROC);
128     }
129 
130     /*
131      * Is a coprocessor op.
132      *
133      * Now we need to determine what type of exception occurred.
134      */
135     for (exception_index=1; exception_index<=MAX_EXCP_REG; exception_index++) {
136 	current_ir = Excp_instr(exception_index);
137 	  /*
138 	   * On PA89: there are 5 different unimplemented exception
139 	   * codes: 0x1, 0x9, 0xb, 0x3, and 0x23.  PA-RISC 2.0 adds
140 	   * another, 0x2b.  Only these have the low order bit set.
141 	   */
142 	excptype = Excp_type(exception_index);
143 	if (excptype & UNIMPLEMENTEDEXCEPTION) {
144 		/*
145 		 * Clear T-bit and exception register so that
146 		 * we can tell if a trap really occurs while
147 		 * emulating the instruction.
148 		 */
149 		Clear_tbit();
150 		Clear_excp_register(exception_index);
151 		/*
152 		 * Now emulate this instruction.  If a trap occurs,
153 		 * fpudispatch will return a non-zero number
154 		 */
155 		excp = fpudispatch(current_ir,excptype,0,Fpu_register);
156 		/* accumulate the status flags, don't lose them as in hpux */
157 		if (excp) {
158 			/*
159 			 * We now need to make sure that the T-bit and the
160 			 * exception register contain the correct values
161 			 * before continuing.
162 			 */
163 			/*
164 			 * Set t-bit since it might still be needed for a
165 			 * subsequent real trap (I don't understand fully -PB)
166 			 */
167 			Set_tbit();
168 			/* some of the following code uses
169 			 * Excp_type(exception_index) so fix that up */
170 			Set_exceptiontype_and_instr_field(excp,current_ir,
171 			 Fpu_register[exception_index]);
172 			if (excp == UNIMPLEMENTEDEXCEPTION) {
173 				/*
174 			 	 * it is really unimplemented, so restore the
175 			 	 * TIMEX extended unimplemented exception code
176 			 	 */
177 				excp = excptype;
178 				update_trap_counts(Fpu_register, aflags, bflags,
179 					   trap_counts);
180 				return SIGNALCODE(SIGILL, ILL_COPROC);
181 			}
182 			/* some of the following code uses excptype, so
183 			 * fix that up too */
184 			excptype = excp;
185 		}
186 		/* handle exceptions other than the real UNIMPLIMENTED the
187 		 * same way as if the hardware had caused them */
188 		if (excp == NOEXCEPTION)
189 			/* For now use 'break', should technically be 'continue' */
190 			break;
191 	}
192 
193 	  /*
194 	   * In PA89, the underflow exception has been extended to encode
195 	   * additional information.  The exception looks like pp01x0,
196 	   * where x is 1 if inexact and pp represent the inexact bit (I)
197 	   * and the round away bit (RA)
198 	   */
199 	if (excptype & UNDERFLOWEXCEPTION) {
200 		/* check for underflow trap enabled */
201 		if (Is_underflowtrap_enabled()) {
202 			update_trap_counts(Fpu_register, aflags, bflags,
203 					   trap_counts);
204 			return SIGNALCODE(SIGFPE, FPE_FLTUND);
205 		} else {
206 		    /*
207 		     * Isn't a real trap; we need to
208 		     * return the default value.
209 		     */
210 		    target = current_ir & fivebits;
211 #ifndef lint
212 		    if (Ibit(Fpu_register[exception_index])) inexact = TRUE;
213 		    else inexact = FALSE;
214 #endif
215 		    switch (Excp_format()) {
216 		      case SGL:
217 		        /*
218 		         * If ra (round-away) is set, will
219 		         * want to undo the rounding done
220 		         * by the hardware.
221 		         */
222 		        if (Rabit(Fpu_register[exception_index]))
223 				Sgl_decrement(Fpu_sgl(target));
224 
225 			/* now denormalize */
226 			sgl_denormalize(&Fpu_sgl(target),&inexact,Rounding_mode());
227 		    	break;
228 		      case DBL:
229 		    	/*
230 		    	 * If ra (round-away) is set, will
231 		    	 * want to undo the rounding done
232 		    	 * by the hardware.
233 		    	 */
234 		    	if (Rabit(Fpu_register[exception_index]))
235 				Dbl_decrement(Fpu_dblp1(target),Fpu_dblp2(target));
236 
237 			/* now denormalize */
238 			dbl_denormalize(&Fpu_dblp1(target),&Fpu_dblp2(target),
239 			  &inexact,Rounding_mode());
240 		    	break;
241 		    }
242 		    if (inexact) Set_underflowflag();
243 		    /*
244 		     * Underflow can generate an inexact
245 		     * exception.  If inexact trap is enabled,
246 		     * want to do an inexact trap, otherwise
247 		     * set inexact flag.
248 		     */
249 		    if (inexact && Is_inexacttrap_enabled()) {
250 		    	/*
251 		    	 * Set exception field of exception register
252 		    	 * to inexact, parm field to zero.
253 			 * Underflow bit should be cleared.
254 		    	 */
255 		    	Set_exceptiontype(Fpu_register[exception_index],
256 			 INEXACTEXCEPTION);
257 			Set_parmfield(Fpu_register[exception_index],0);
258 			update_trap_counts(Fpu_register, aflags, bflags,
259 					   trap_counts);
260 			return SIGNALCODE(SIGFPE, FPE_FLTRES);
261 		    }
262 		    else {
263 		    	/*
264 		    	 * Exception register needs to be cleared.
265 			 * Inexact flag needs to be set if inexact.
266 		    	 */
267 		    	Clear_excp_register(exception_index);
268 		    	if (inexact) Set_inexactflag();
269 		    }
270 		}
271 		continue;
272 	}
273 	switch(Excp_type(exception_index)) {
274 	  case OVERFLOWEXCEPTION:
275 	  case OVERFLOWEXCEPTION | INEXACTEXCEPTION:
276 		/* check for overflow trap enabled */
277 			update_trap_counts(Fpu_register, aflags, bflags,
278 					   trap_counts);
279 		if (Is_overflowtrap_enabled()) {
280 			update_trap_counts(Fpu_register, aflags, bflags,
281 					   trap_counts);
282 			return SIGNALCODE(SIGFPE, FPE_FLTOVF);
283 		} else {
284 			/*
285 			 * Isn't a real trap; we need to
286 			 * return the default value.
287 			 */
288 			target = current_ir & fivebits;
289 			switch (Excp_format()) {
290 			  case SGL:
291 				Sgl_setoverflow(Fpu_sgl(target));
292 				break;
293 			  case DBL:
294 				Dbl_setoverflow(Fpu_dblp1(target),Fpu_dblp2(target));
295 				break;
296 			}
297 			Set_overflowflag();
298 			/*
299 			 * Overflow always generates an inexact
300 			 * exception.  If inexact trap is enabled,
301 			 * want to do an inexact trap, otherwise
302 			 * set inexact flag.
303 			 */
304 			if (Is_inexacttrap_enabled()) {
305 				/*
306 				 * Set exception field of exception
307 				 * register to inexact.  Overflow
308 				 * bit should be cleared.
309 				 */
310 				Set_exceptiontype(Fpu_register[exception_index],
311 				 INEXACTEXCEPTION);
312 				update_trap_counts(Fpu_register, aflags, bflags,
313 					   trap_counts);
314 				return SIGNALCODE(SIGFPE, FPE_FLTRES);
315 			}
316 			else {
317 				/*
318 				 * Exception register needs to be cleared.
319 				 * Inexact flag needs to be set.
320 				 */
321 				Clear_excp_register(exception_index);
322 				Set_inexactflag();
323 			}
324 		}
325 		break;
326 	  case INVALIDEXCEPTION:
327 	  case OPC_2E_INVALIDEXCEPTION:
328 		update_trap_counts(Fpu_register, aflags, bflags, trap_counts);
329 		return SIGNALCODE(SIGFPE, FPE_FLTINV);
330 	  case DIVISIONBYZEROEXCEPTION:
331 		update_trap_counts(Fpu_register, aflags, bflags, trap_counts);
332 		Clear_excp_register(exception_index);
333 	  	return SIGNALCODE(SIGFPE, FPE_FLTDIV);
334 	  case INEXACTEXCEPTION:
335 		update_trap_counts(Fpu_register, aflags, bflags, trap_counts);
336 		return SIGNALCODE(SIGFPE, FPE_FLTRES);
337 	  default:
338 		update_trap_counts(Fpu_register, aflags, bflags, trap_counts);
339 		printk("%s(%d) Unknown FPU exception 0x%x\n", __FILE__,
340 			__LINE__, Excp_type(exception_index));
341 		return SIGNALCODE(SIGILL, ILL_COPROC);
342 	  case NOEXCEPTION:	/* no exception */
343 		/*
344 		 * Clear exception register in case
345 		 * other fields are non-zero.
346 		 */
347 		Clear_excp_register(exception_index);
348 		break;
349 	}
350     }
351     /*
352      * No real exceptions occurred.
353      */
354     Clear_tbit();
355     update_trap_counts(Fpu_register, aflags, bflags, trap_counts);
356     return(NOTRAP);
357 }
358