walkcontext(3C) Standard C Library Functions walkcontext(3C)NAME
walkcontext, printstack - walk stack pointed to by ucontext
SYNOPSIS
#include <ucontext.h>
int walkcontext(const ucontext_t *uptr, int (*operate_func)(uintptr_t,
int, void *), void *usrarg);
int printstack(int fd);
DESCRIPTION
The walkcontext() function walks the call stack pointed to by uptr,
which can be obtained by a call to getcontext(2) or from a signal han‐
dler installed with the SA_SIGINFO flag. The walkcontext() function
calls the user-supplied function operate_func for each routine found on
the call stack and each signal handler invoked. The user function is
passed three arguments: the PC at which the call or signal occured, the
signal number that occured at this PC (0 if no signal occured), and the
third argument passed to walkcontext(). If the user function returns a
non-zero value, walkcontext() returns without completing the callstack
walk.
The printstack() function uses walkcontext() to print a symbolic stack
trace to the specified file descriptor. This is useful for reporting
errors from signal handlers. The printstack() function uses dladdr1()
(see dladdr(3C)) to obtain symbolic symbol names. As a result, only
global symbols are reported as symbol names by printstack().
RETURN VALUES
Upon successful completion, walkcontext() and printstack() return 0.
If walkcontext() cannot read the stack or the stack trace appears cor‐
rupted, both functions return -1.
ERRORS
No error values are defined.
USAGE
The walkcontext() function is typically used to obtain information
about the call stack for error reporting, performance analysis, or
diagnostic purposes. Many library functions are not Async-Signal-Safe
and should not be used from a signal handler. If walkcontext() is to be
called from a signal handler, careful programming is required. In par‐
ticular, stdio(3C) and malloc(3C) cannot be used.
The printstack() function is Async-Signal-Safe and can be called from a
signal handler. The output format from printstack() is unstable, as it
varies with the scope of the routines.
Tail-call optimizations on SPARC eliminate stack frames that would oth‐
erwise be present. For example, if the code is of the form
#include <stdio.h>
main()
{
bar();
exit(0);
}
bar()
{
int a;
a = foo(fileno(stdout));
return (a);
}
foo(int file)
{
printstack(file);
}
compiling without optimization will yield a stack trace of the form
/tmp/q:foo+0x8
/tmp/q:bar+0x14
/tmp/q:main+0x4
/tmp/q:_start+0xb8
whereas with higher levels of optimization the output is
/tmp/q:main+0x10
/tmp/q:_start+0xb8
since both the call to foo() in main and the call to bar() in foo() are
handled as tail calls that perform a return or restore in the delay
slot. For further information, see The SPARC Architecture Manual.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Stable │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │Async-Signal-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOintro(2), getcontext(2), sigaction(2), dladdr(3C), siginfo.h(3HEAD),
attributes(5)
Weaver, David L. and Tom Germond, eds. The SPARC Architecture Manual,
Version 9. Santa Clara: Prentice Hall, 2000.
SunOS 5.10 1 Mar 2004 walkcontext(3C)
