fex_set_log(3M) Mathematical Library Functions fex_set_log(3M)NAME
fex_set_log, fex_get_log, fex_set_log_depth, fex_get_log_depth,
fex_log_entry - log retrospective diagnostics for floating point excep‐
tions
SYNOPSIS
c99 [ flag... ] file... -lm [ library... ]
#include <fenv.h>
int fex_set_log(FILE *fp);
FILE *fex_get_log(void);
int fex_set_log_depth(int depth);
int fex_get_log_depth(void);
void fex_log_entry(const char *msg);
DESCRIPTION
The fex_set_log() function enables logging of retrospective diagnostic
messages regarding floating point exceptions to the file specified by
fp. If fp is NULL, logging is disabled. When a program starts, log‐
ging is initially disabled.
The occurrence of any of the twelve exceptions listed in fex_set_han‐
dling(3M) constitutes an event that can be logged. To prevent the log
from becoming exhorbitantly long, the logging mechanism eliminates
redundant entries by two methods. First, each exception is associated
with a site in the program. The site is identified by the address of
the instruction that caused the exception together with a stack trace.
Only the first exception of a given type to occur at a given site will
be logged. Second, when FEX_NONSTOP handling mode is in effect for
some exception, only those occurrences of that exception that set its
previously clear flag are logged. Clearing a flag using feclearex‐
cept() allows the next occurrence of the exception to be logged pro‐
vided it does not occur at a site at which it was previously logged.
Each of the different types of invalid operation exceptions can be
logged at the same site. Because all invalid operation exceptions
share the same flag, however, of those types for which FEX_NONSTOP mode
is in effect, only the first exception to set the flag will be logged.
When the invalid operation exception is raised by a call to feraiseex‐
cept(3M) or feupdateenv(3M), which type of invalid operation is logged
depends on the implementation.
If an exception results in the creation of a log entry, the entry is
created at the time the exception occurs and before any exception han‐
dling actions selected with fex_set_handling() are taken. In particu‐
lar, the log entry is available even if the program terminates as a
result of the exception. The log entry shows the type of exception,
the address of the instruction that caused it, how it will be handled,
and the stack trace. If symbols are available, the address of the
excepting instruction and the addresses in the stack trace are followed
by the names of the corresponding symbols.
The fex_get_log() function returns the current log file.
The fex_set_log_depth() sets the maximum depth of the stack trace
recorded with each exception to depth stack frames. The default depth
is 100.
Thefex_get_log_depth() function returns the current maximum stack trace
depth.
The fex_log_entry() function adds a user-supplied entry to the log.
The entry includes the string pointed to by msg and the stack trace.
Like entries for floating point exceptions, redundant user-supplied
entries are eliminated: only the first user-supplied entry with a given
msg to be requested from a given site will be logged. For the purpose
of a user-supplied entry, the site is defined only by the stack trace,
which begins with the function that called fex_log_entry().
RETURN VALUES
The fex_set_log() function returns a non-zero value if logging is
enabled or disabled accordingly and returns 0 otherwise. The
fex_set_log_depth() returns a non-zero value if the requested stack
trace depth is established (regardless of whether logging is enabled)
and returns 0 otherwise.
EXAMPLES
The following example demonstrates the output generated when a floating
point overflow occurs in sscanf(3C).
#include <fenv.h>
int
main() {
double x;
/*
* enable logging of retrospective diagnostics
*/
(void) fex_set_log(stdout);
/*
* establish default handling for overflows
*/
(void) fex_set_handling(FEX_OVERFLOW, FEX_NONSTOP, NULL);
/*
* trigger an overflow in sscanf
*/
(void) sscanf("1.0e+400", "%lf", &x);
return 0;
}
The output from the preceding program reads:
Floating point overflow at 0xef71cac4 __base_conversion_set_exceptio
n, nonstop mode
0xef71cacc __base_conversion_set_exception
0xef721820 _decimal_to_double
0xef75aba8 number
0xef75a94c __doscan_u
0xef75ecf8 sscanf
0x00010f20 main
Recompiling the program or running it on another system can produce
different text addresses from those shown above.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────────────────────────────────────────────┐
│ATTRIBUTE TYPE ATTRIBUTE VALUE │
│Availability system/library/math, SUNWlmxs │
│Interface Stability Committed │
│MT-Level MT-Safe (see NOTES) │
└────────────────────────────────────────────────────────────┘
SEE ALSOfeclearexcept(3M), fegetenv(3M), feraiseexcept(3M), feupdateenv(3M),
fex_set_handling(3M), attributes(5)
Numerical Computation Guide
NOTES
All threads in a process share the same log file. Each call to
fex_set_log() preempts the previous one.
In addition to the log file itself, two additional file descriptors are
used during the creation of a log entry in order to obtain symbol names
from the executable and any shared objects it uses. These file
descriptors are relinquished once the log entry is written. If the
file descriptors cannot be allocated, symbols names are omitted from
the stack trace.
The functions described on this page automatically install and dein‐
stall SIGFPE handlers and set and clear the trap enable mode bits in
the floating point status register as needed. If a program uses these
functions and attempts to install a SIGFPE handler or control the trap
enable mode bits independently, the resulting behavior is not defined.
As described in fex_set_handling(), when a handling function installed
in FEX_CUSTOM mode is invoked, all exception traps are disabled (and
will not be reenabled while SIGFPE is blocked). Thus, retrospective
diagnostic messages are not logged for exceptions that occur within
such a handler.
SunOS 5.11 12 Jul 2006 fex_set_log(3M)
