Stack traces
You are encouraged to solve this task according to the task description, using any language you may know.
Many programming languages allow for introspection of the current call stack environment. This can be for a variety of purposes such as enforcing security checks, debugging, or for getting access to the stack frame of callers.
This task calls for you to print out (in a manner considered suitable for the platform) the current call stack. The amount of information printed for each frame on the call stack is not constrained, but should include at least the name of the function or method at that level of the stack frame. You may explicitly add a call to produce the stack trace to the (example) code being instrumented for examination.
C
The backtrace* functions are a GNU extension to the standard C library.
In order to be able to see the symbols, we need to link with an option telling to export symbols names in the dynamic section (for ELF and targets supporting it); for gcc, it means using the option -rdynamic (or -export-dynamic in the GNU linker). Otherwise we see only addresses. Static functions will always have their names "hidden".
<lang c>#include <stdio.h>
- include <stdlib.h>
- include <unistd.h>
- include <execinfo.h>
- define MAX_BT 200
void print_stack_trace() {
void *buffer[MAX_BT]; int n;
n = backtrace(buffer, MAX_BT); fprintf(stderr, "--- (depth %d) ---\n", n); backtrace_symbols_fd(buffer, n, STDERR_FILENO);
}
void inner(int k)
{
print_stack_trace();
}
void middle(int x, int y) {
inner(x*y);
}
void outer(int a, int b, int c) {
middle(a+b, b+c);
}
int main() {
outer(2,3,5); return EXIT_SUCCESS;
}</lang>
Sample output on my system:
--- (depth 7) --- ./pst(print_stack_trace+0x1f)[0x8048683] ./pst(inner+0xb)[0x80486cd] ./pst(middle+0x15)[0x80486e4] ./pst(outer+0x23)[0x8048709] ./pst(main+0x2d)[0x8048738] /lib/i686/libc.so.6(__libc_start_main+0xe5)[0xb7e045c5] ./pst[0x80485d1]
Java
<lang java>public class StackTracer {
public static void printStackTrace() {
StackTraceElement elems = Thread.currentThread().getStackTrace();
System.out.println("Stack trace:"); for (int i = elems.length-1, j = 2 ; i >= 1 ; i--, j+=2) { System.out.printf("%" + j + "s%s.%s%n", "", elems[i].getClassName(), elems[i].getMethodName()); }
}
}</lang>
Python
see the traceback module <lang python>import traceback
traceback.print_stack()</lang>
Ruby
<lang ruby>begin
raise "boom"
rescue => detail
puts detail.backtrace.join("\n")
end</lang>
Smalltalk
A backtrace is normally sent when some error occurs; however, it can be "forced":
<lang smalltalk>Object subclass: Container [
Container class >> outer: a and: b and: c [
self middle: (a+b) and: (b+c)
]
Container class >> middle: x and: y [
self inner: (x*y)
]
Container class >> inner: k [
Smalltalk backtrace
]
].
Container outer: 2 and: 3 and: 5.</lang>
Tcl
<lang tcl>proc printStackTrace {} {
puts "Stack trace:"
for {set i 1} {$i < [info level]} {incr i} {
puts [string repeat " " $i][info level $i]
}
}</lang> Demonstration code: <lang tcl>proc outer {a b c} {
middle [expr {$a+$b}] [expr {$b+$c}]
} proc middle {x y} {
inner [expr {$x*$y}]
} proc inner k {
printStackTrace
} outer 2 3 5</lang> Produces this output:
Stack trace:
outer 2 3 5
middle 5 8
inner 40