profil(buff, bufsiz, offset, scale)
int bufsiz, offset, scale;
Buff points to an area of core whose length (in bytes) is given by bufsiz. After this call, the user's program counter (pc) is examined
each clock tick (VAX and TAHOE: 100 ticks/second = 10 milliseconds per tick; 60 ticks/second ~= 16 milliseconds per tick); offset is sub-
tracted from it, and the result multiplied by scale. If the resulting number corresponds to a word inside buff, that word is incremented.
The scale is interpreted as an unsigned, fixed-point fraction with 16 bits of fraction: 0xffff gives a 1-1 mapping of pc's to words in
buff; 0x7fff maps each pair of instruction words together.
Profiling is turned off by giving a scale of 0 or 1. It is rendered ineffective by giving a bufsiz of 0. Profiling is turned off when an
execve is executed, but remains on in child and parent both after a fork. Profiling is turned off if an update in buff would cause a mem-