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profil(2) System Calls Manual profil(2) NAME profil - Starts and stops execution profiling SYNOPSIS void profil( unsigned short *short_buffer, unsigned int buffer_size, void *offset, unsigned int scale ); #include <sys/resource.h> void profil( struct profil_args *args, int buffer_size, -1, unsigned long flags); PARAMETERS Points to an area of memory in the user address space. Its length (in bytes) is given by the buffer_size parameter. Specifies the length (in bytes) of the buffer. When offset is -1, indicating that the extended profil format shown in the second synopsis above is in use, the buffer_size parameter indicates the number of profil_args structures in the args array. Specifies the delta of program counter start and buffer; for example, an offset of 0 (zero) implies that text begins at 0. When offset is -1, the profil call is interpreted as a call to pro- file multiple discontiguous address ranges, such as those in an exe- cutable and its shared libraries. In this type of profil call, which has the format shown in the second synopsis above, the buffer_size pa- rameter indicates the number of profil_args structures in the args ar- ray. Specifies the mapping factor between the program counter and short_buffer. When offset is -1, specifies an array of up to 64 struct profil_args structures, each describing a single address range in which profiling is to occur. Specifies flags that modify the behavior of a profil call that profiles multiple discontiguous address ranges. This argument is reserved for future use and should be 0. DESCRIPTION The profil() function controls execution profiling. The short_buffer parameter points to an area of memory whose length (in bytes) is given by the buffer_size parameter. After this call, the process' program counter is examined at regular intervals (for example, at 1024 Hz). To determine the interval for your system, use the get- sysinfo(2) system call with GSI_CLK_TCK as the operation parameter. The value of the offset parameter is subtracted from the program counter, and the result multiplied by the scale parameter. The corre- sponding location in the short_buffer parameter is incremented if the resulting number is less than the buffer_size parameter. The scale parameter is interpreted as an unsigned, fixed point fraction with 16 bits of mantissa: 0x10000 means that the address range has the same number of bytes as the short_buffer (that is, two bytes of in- struction map into each short_buffer element); 0x8000 maps four bytes of instructions into each short_buffer element; and so on. The special scale factor of 2 maps all instructions onto the beginning of the short_buffer (producing a non-interrupting clock). Profiling is turned off by giving a scale parameter of either zero (0) or 1. Profiling is turned off when an execve() is executed. Profiling remains on in both the parent and child processes after a fork. Pro- filing is turned off if an update in the short_buffer parameter would cause a memory fault. If the process contains multiple threads, each will be independently sampled and the counts will reflect the sum of the samples for all of the threads. The second form of profil call allows you to profile multiple disjoint address ranges, such as an executable and its shared libraries. This form of profil call must specify an offset of -1. Its first argument, args, specifies an array of struct profil_args structures, each de- scribing a single address range in which profiling is to occur. The buffer_size argument indicates the number of profil_args structures in the args array. The members of each profil_args structure in the array pointed to by args are similar to the arguments in the traditional profil call, ex- cept that the buffer field is an array of unsigned ints instead of an array of unsigned shorts, and the highpc and lowpc members specify both ends of the address range to be profiled. The scale is still the ratio of bytes in the address range to bytes in the buffer. The following are the contents of a profil_args struct: struct profil_args { unsigned int *buffer; void *highpc; void *lowpc void *offset; unsigned int scale; } All the address ranges specified in the array must be non-overlapping, and be ordered by decreasing lowpc value (that is, addresses ranges ap- pear in the array in decreasing beginning address order). As with a traditional profil call, profiling is turned off (for a given address range) if an update in the buffer (specified by the struct profil_args for that address range) would cause a memory fault. You can stop profiling started by either type of profil call by issuing the following command: profil(0,0,0,0) Because a traditional profil call stops all profiling started with an extended call, and an extended profil call stops all profiling started with a traditional call, a thread never needs to record both kinds of profiling activity at the same time. That is, profiling a single ad- dress range with a buffer of short counters and profiling multiple ad- dress ranges in buffers with int counters are mutually exclusive in a given thread. Although a thread can be switched from one type of pro- filing to the other with any call to the other interface and different profiling mechanisms can operate on separate threads simultaneously, use of a single profiling interface is recommended in a single applica- tion. RELATED INFORMATION Functions: exec(2), fork(2), getsysinfo(2), monitor(3) Commands: prof(1) delim off profil(2)