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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 1.5 2005/11/13 01:18:20 swildner 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; may be static, inline, etc
68 _MCOUNT_DECL(uintfptr_t frompc, uintfptr_t selfpc)
75 struct tostruct *top, *prevtop;
83 #ifndef GUPROF /* XXX */
85 * check that we are profiling
86 * and that we aren't recursively invoked.
88 if (p->state != GMON_PROF_ON)
94 p->state = GMON_PROF_BUSY;
96 frompci = frompc - p->lowpc;
100 * When we are called from an exception handler, frompci may be
101 * for a user address. Convert such frompci's to the index of
102 * user() to merge all user counts.
104 if (frompci >= p->textsize) {
105 if (frompci + p->lowpc
106 >= (uintfptr_t)(VM_MAXUSER_ADDRESS + UPAGES * PAGE_SIZE))
108 frompci = (uintfptr_t)user - p->lowpc;
109 if (frompci >= p->textsize)
115 if (p->state != GMON_PROF_HIRES)
116 goto skip_guprof_stuff;
118 * Look at the clock and add the count of clock cycles since the
119 * clock was last looked at to a counter for frompc. This
120 * solidifies the count for the function containing frompc and
121 * effectively starts another clock for the current function.
122 * The count for the new clock will be solidified when another
123 * function call is made or the function returns.
125 * We use the usual sampling counters since they can be located
126 * efficiently. 4-byte counters are usually necessary.
128 * There are many complications for subtracting the profiling
129 * overheads from the counts for normal functions and adding
130 * them to the counts for mcount(), mexitcount() and cputime().
131 * We attempt to handle fractional cycles, but the overheads
132 * are usually underestimated because they are calibrated for
133 * a simpler than usual setup.
135 delta = cputime() - p->mcount_overhead;
136 p->cputime_overhead_resid += p->cputime_overhead_frac;
137 p->mcount_overhead_resid += p->mcount_overhead_frac;
139 *p->mcount_count += delta + p->mcount_overhead
140 - p->cputime_overhead;
141 else if (delta != 0) {
142 if (p->cputime_overhead_resid >= CALIB_SCALE) {
143 p->cputime_overhead_resid -= CALIB_SCALE;
148 if (p->mcount_overhead_resid >= CALIB_SCALE) {
149 p->mcount_overhead_resid -= CALIB_SCALE;
153 KCOUNT(p, frompci) += delta;
155 *p->mcount_count += p->mcount_overhead_sub;
157 *p->cputime_count += p->cputime_overhead;
163 * When we are called from an exception handler, frompc is faked
164 * to be for where the exception occurred. We've just solidified
165 * the count for there. Now convert frompci to the index of btrap()
166 * for trap handlers and bintr() for interrupt handlers to make
167 * exceptions appear in the call graph as calls from btrap() and
168 * bintr() instead of calls from all over.
170 if ((uintfptr_t)selfpc >= (uintfptr_t)btrap
171 && (uintfptr_t)selfpc < (uintfptr_t)eintr) {
172 if ((uintfptr_t)selfpc >= (uintfptr_t)bintr)
173 frompci = (uintfptr_t)bintr - p->lowpc;
175 frompci = (uintfptr_t)btrap - p->lowpc;
180 * check that frompc is a reasonable pc value.
181 * for example: signal catchers get called from the stack,
182 * not from text space. too bad.
184 if (frompci >= p->textsize)
187 frompcindex = &p->froms[frompci / (p->hashfraction * sizeof(*p->froms))];
188 toindex = *frompcindex;
191 * first time traversing this arc
193 toindex = ++p->tos[0].link;
194 if (toindex >= p->tolimit)
195 /* halt further profiling */
198 *frompcindex = toindex;
199 top = &p->tos[toindex];
200 top->selfpc = selfpc;
205 top = &p->tos[toindex];
206 if (top->selfpc == selfpc) {
208 * arc at front of chain; usual case.
214 * have to go looking down chain for it.
215 * top points to what we are looking at,
216 * prevtop points to previous top.
217 * we know it is not at the head of the chain.
219 for (; /* goto done */; ) {
220 if (top->link == 0) {
222 * top is end of the chain and none of the chain
223 * had top->selfpc == selfpc.
224 * so we allocate a new tostruct
225 * and link it to the head of the chain.
227 toindex = ++p->tos[0].link;
228 if (toindex >= p->tolimit)
231 top = &p->tos[toindex];
232 top->selfpc = selfpc;
234 top->link = *frompcindex;
235 *frompcindex = toindex;
239 * otherwise, check the next arc on the chain.
242 top = &p->tos[top->link];
243 if (top->selfpc == selfpc) {
246 * increment its count
247 * move it to the head of the chain.
250 toindex = prevtop->link;
251 prevtop->link = top->link;
252 top->link = *frompcindex;
253 *frompcindex = toindex;
262 p->state = GMON_PROF_ON;
266 p->state = GMON_PROF_ERROR;
274 * Actual definition of mcount function. Defined in <machine/profile.h>,
275 * which is included by <sys/gmon.h>.
281 mexitcount(uintfptr_t selfpc)
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;