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33 * @(#)mcount.c 8.1 (Berkeley) 6/4/93
34 * $FreeBSD: src/lib/libc/gmon/mcount.c,v 1.17 1999/12/29 05:04:13 peter Exp $
35 * $DragonFly: src/lib/libc/gmon/mcount.c,v 1.4 2004/10/25 19:38:01 drhodus Exp $
38 #include <sys/param.h>
41 #include <sys/systm.h>
43 #include <vm/vm_param.h>
52 * mcount is called on entry to each function compiled with the profiling
53 * switch set. _mcount(), which is declared in a machine-dependent way
54 * with _MCOUNT_DECL, does the actual work and is either inlined into a
55 * C routine or called by an assembly stub. In any case, this magic is
56 * taken care of by the MCOUNT definition in <machine/profile.h>.
58 * _mcount updates data structures that represent traversals of the
59 * program's call graph edges. frompc and selfpc are the return
60 * address and function address that represents the given call graph edge.
62 * Note: the original BSD code used the same variable (frompcindex) for
63 * both frompcindex and frompc. Any reasonable, modern compiler will
64 * perform this optimization.
66 _MCOUNT_DECL(frompc, selfpc) /* _mcount; may be static, inline, etc */
67 uintfptr_t frompc, selfpc;
74 struct tostruct *top, *prevtop;
82 #ifndef GUPROF /* XXX */
84 * check that we are profiling
85 * and that we aren't recursively invoked.
87 if (p->state != GMON_PROF_ON)
93 p->state = GMON_PROF_BUSY;
95 frompci = frompc - p->lowpc;
99 * When we are called from an exception handler, frompci may be
100 * for a user address. Convert such frompci's to the index of
101 * user() to merge all user counts.
103 if (frompci >= p->textsize) {
104 if (frompci + p->lowpc
105 >= (uintfptr_t)(VM_MAXUSER_ADDRESS + UPAGES * PAGE_SIZE))
107 frompci = (uintfptr_t)user - p->lowpc;
108 if (frompci >= p->textsize)
114 if (p->state != GMON_PROF_HIRES)
115 goto skip_guprof_stuff;
117 * Look at the clock and add the count of clock cycles since the
118 * clock was last looked at to a counter for frompc. This
119 * solidifies the count for the function containing frompc and
120 * effectively starts another clock for the current function.
121 * The count for the new clock will be solidified when another
122 * function call is made or the function returns.
124 * We use the usual sampling counters since they can be located
125 * efficiently. 4-byte counters are usually necessary.
127 * There are many complications for subtracting the profiling
128 * overheads from the counts for normal functions and adding
129 * them to the counts for mcount(), mexitcount() and cputime().
130 * We attempt to handle fractional cycles, but the overheads
131 * are usually underestimated because they are calibrated for
132 * a simpler than usual setup.
134 delta = cputime() - p->mcount_overhead;
135 p->cputime_overhead_resid += p->cputime_overhead_frac;
136 p->mcount_overhead_resid += p->mcount_overhead_frac;
138 *p->mcount_count += delta + p->mcount_overhead
139 - p->cputime_overhead;
140 else if (delta != 0) {
141 if (p->cputime_overhead_resid >= CALIB_SCALE) {
142 p->cputime_overhead_resid -= CALIB_SCALE;
147 if (p->mcount_overhead_resid >= CALIB_SCALE) {
148 p->mcount_overhead_resid -= CALIB_SCALE;
152 KCOUNT(p, frompci) += delta;
154 *p->mcount_count += p->mcount_overhead_sub;
156 *p->cputime_count += p->cputime_overhead;
162 * When we are called from an exception handler, frompc is faked
163 * to be for where the exception occurred. We've just solidified
164 * the count for there. Now convert frompci to the index of btrap()
165 * for trap handlers and bintr() for interrupt handlers to make
166 * exceptions appear in the call graph as calls from btrap() and
167 * bintr() instead of calls from all over.
169 if ((uintfptr_t)selfpc >= (uintfptr_t)btrap
170 && (uintfptr_t)selfpc < (uintfptr_t)eintr) {
171 if ((uintfptr_t)selfpc >= (uintfptr_t)bintr)
172 frompci = (uintfptr_t)bintr - p->lowpc;
174 frompci = (uintfptr_t)btrap - p->lowpc;
179 * check that frompc is a reasonable pc value.
180 * for example: signal catchers get called from the stack,
181 * not from text space. too bad.
183 if (frompci >= p->textsize)
186 frompcindex = &p->froms[frompci / (p->hashfraction * sizeof(*p->froms))];
187 toindex = *frompcindex;
190 * first time traversing this arc
192 toindex = ++p->tos[0].link;
193 if (toindex >= p->tolimit)
194 /* halt further profiling */
197 *frompcindex = toindex;
198 top = &p->tos[toindex];
199 top->selfpc = selfpc;
204 top = &p->tos[toindex];
205 if (top->selfpc == selfpc) {
207 * arc at front of chain; usual case.
213 * have to go looking down chain for it.
214 * top points to what we are looking at,
215 * prevtop points to previous top.
216 * we know it is not at the head of the chain.
218 for (; /* goto done */; ) {
219 if (top->link == 0) {
221 * top is end of the chain and none of the chain
222 * had top->selfpc == selfpc.
223 * so we allocate a new tostruct
224 * and link it to the head of the chain.
226 toindex = ++p->tos[0].link;
227 if (toindex >= p->tolimit)
230 top = &p->tos[toindex];
231 top->selfpc = selfpc;
233 top->link = *frompcindex;
234 *frompcindex = toindex;
238 * otherwise, check the next arc on the chain.
241 top = &p->tos[top->link];
242 if (top->selfpc == selfpc) {
245 * increment its count
246 * move it to the head of the chain.
249 toindex = prevtop->link;
250 prevtop->link = top->link;
251 top->link = *frompcindex;
252 *frompcindex = toindex;
261 p->state = GMON_PROF_ON;
265 p->state = GMON_PROF_ERROR;
273 * Actual definition of mcount function. Defined in <machine/profile.h>,
274 * which is included by <sys/gmon.h>.
284 uintfptr_t selfpcdiff;
287 selfpcdiff = selfpc - (uintfptr_t)p->lowpc;
288 if (selfpcdiff < p->textsize) {
292 * Solidify the count for the current function.
294 delta = cputime() - p->mexitcount_overhead;
295 p->cputime_overhead_resid += p->cputime_overhead_frac;
296 p->mexitcount_overhead_resid += p->mexitcount_overhead_frac;
298 *p->mexitcount_count += delta + p->mexitcount_overhead
299 - p->cputime_overhead;
300 else if (delta != 0) {
301 if (p->cputime_overhead_resid >= CALIB_SCALE) {
302 p->cputime_overhead_resid -= CALIB_SCALE;
307 if (p->mexitcount_overhead_resid
309 p->mexitcount_overhead_resid
311 ++*p->mexitcount_count;
314 KCOUNT(p, selfpcdiff) += delta;
316 *p->mexitcount_count += p->mexitcount_overhead_sub;
318 *p->cputime_count += p->cputime_overhead;