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 handler 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 corrupted, 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 particular, 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 otherwise 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:

See Also

Intro(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.