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29 * @(#)mcount.c 8.1 (Berkeley) 6/4/93
30 * $FreeBSD: src/lib/libc/gmon/mcount.c,v 1.20 2004/10/16 06:32:43 obrien Exp $
33 #include <sys/param.h>
37 * mcount is called on entry to each function compiled with the profiling
38 * switch set. _mcount(), which is declared in a machine-dependent way
39 * with _MCOUNT_DECL, does the actual work and is either inlined into a
40 * C routine or called by an assembly stub. In any case, this magic is
41 * taken care of by the MCOUNT definition in <machine/profile.h>.
43 * _mcount updates data structures that represent traversals of the
44 * program's call graph edges. frompc and selfpc are the return
45 * address and function address that represents the given call graph edge.
47 * Note: the original BSD code used the same variable (frompcindex) for
48 * both frompcindex and frompc. Any reasonable, modern compiler will
49 * perform this optimization.
51 /* _mcount; may be static, inline, etc */
52 _MCOUNT_DECL(u_long frompc, u_long selfpc)
56 struct tostruct *top, *prevtop;
62 * check that we are profiling
63 * and that we aren't recursively invoked.
65 if (p->state != GMON_PROF_ON)
67 p->state = GMON_PROF_BUSY; /* XXX */
68 frompci = frompc - p->lowpc;
71 * check that frompc is a reasonable pc value.
72 * for example: signal catchers get called from the stack,
73 * not from text space. too bad.
75 if (frompci >= p->textsize)
78 frompcindex = &p->froms[frompci / (p->hashfraction * sizeof(*p->froms))];
79 toindex = *frompcindex;
82 * first time traversing this arc
84 toindex = ++p->tos[0].link;
85 if (toindex >= p->tolimit)
86 /* halt further profiling */
89 *frompcindex = toindex;
90 top = &p->tos[toindex];
96 top = &p->tos[toindex];
97 if (top->selfpc == selfpc) {
99 * arc at front of chain; usual case.
105 * have to go looking down chain for it.
106 * top points to what we are looking at,
107 * prevtop points to previous top.
108 * we know it is not at the head of the chain.
110 for (; /* goto done */; ) {
111 if (top->link == 0) {
113 * top is end of the chain and none of the chain
114 * had top->selfpc == selfpc.
115 * so we allocate a new tostruct
116 * and link it to the head of the chain.
118 toindex = ++p->tos[0].link;
119 if (toindex >= p->tolimit)
122 top = &p->tos[toindex];
123 top->selfpc = selfpc;
125 top->link = *frompcindex;
126 *frompcindex = toindex;
130 * otherwise, check the next arc on the chain.
133 top = &p->tos[top->link];
134 if (top->selfpc == selfpc) {
137 * increment its count
138 * move it to the head of the chain.
141 toindex = prevtop->link;
142 prevtop->link = top->link;
143 top->link = *frompcindex;
144 *frompcindex = toindex;
150 p->state = GMON_PROF_ON; /* XXX */
153 p->state = GMON_PROF_ERROR; /* XXX */
158 * Actual definition of mcount function. Defined in <machine/profile.h>,
159 * which is included by <sys/gmon.h>.