Zheng Da wrote:
I wrote a simple one as follow:
<snip>
Sorry, your code does not compile; you forgot to
#include <stdio.h>
and you use the non-standard __asm__() function.
When the computer execute jmp %2, and gives me a segment fault.
Why the address I save is a invalid address?
By the way, I want to find the codes of setjmp and longjmp in glibc,
but can not get it, and waht I find does not seem to be what I want.
How to find the codes of setjmp and longjmp which can run under Linux
and x86?
Please provide a minimal compiling example in standard
C or repost your request in a newsgroup where your
platform/operating system/compiler-combination is on-topic.
Information about setjmp/longjmp() can be found below.
Cheers
Michael
PS: The following is only a quote from the standard.
As for setjmp()/longjmp():
7.13 Nonlocal jumps <setjmp.h>
1 The header <setjmp.h> defines the macro setjmp, and declares one
function and one type, for bypassing the normal function call and
return discipline.207)
,---
| 207) These functions are useful for dealing with unusual conditions
| encountered in a low-level function of a program.
`---
2 The type declared is
jmp_buf
which is an array type suitable for holding the information needed to
restore a calling environment. The environment of a call to the setjmp
macro consists of information sufficient for a call to the longjmp
function to return execution to the correct block and invocation of that
block, were it called recursively. It does not include the state of the
floating-point status flags, of open files, or of any other component of
the abstract machine.
3 It is unspecified whether setjmp is a macro or an identifier declared
with external linkage. If a macro definition is suppressed in order to
access an actual function, or a program defines an external identifier
with the name setjmp, the behavior is undefined.
7.13.1 Save calling environment
7.13.1.1 The setjmp macro
Synopsis
1
#include <setjmp.h>
int setjmp(jmp_buf env);
Description
2 The setjmp macro saves its calling environment in its jmp_buf argument
for later use by the longjmp function.
Returns
3 If the return is from a direct invocation, the setjmp macro returns
the value zero. If the return is from a call to the longjmp function,
the setjmp macro returns a nonzero value.
Environmental limits
4 An invocation of the setjmp macro shall appear only in one of the
following contexts:
— the entire controlling expression of a selection or iteration
statement;
— one operand of a relational or equality operator with the other
operand an integer constant expression, with the resulting expression
being the entire controlling expression of a selection or iteration
statement;
— the operand of a unary ! operator with the resulting expression being
the entire controlling expression of a selection or iteration
statement; or
— the entire expression of an expression statement (possibly cast to
void).
5 If the invocation appears in any other context, the behavior is undefined.
7.13.2 Restore calling environment
7.13.2.1 The longjmp function
Synopsis
1
#include <setjmp.h>
void longjmp(jmp_buf env, int val);
Description
2 The longjmp function restores the environment saved by the most recent
invocation of the setjmp macro in the same invocation of the program
with the corresponding jmp_buf argument. If there has been no such
invocation, or if the function containing the invocation of the setjmp
macro has terminated execution208) in the interim, or if the invocation
of the setjmp macro was within the scope of an identifier with variably
modified type and execution has left that scope in the interim, the
behavior is undefined.
,---
| 208) For example, by executing a return statement or because another
| longjmp call has caused a transfer to a setjmp invocation in a
| function earlier in the set of nested calls.
`---
3 All accessible objects have values, and all other components of the
abstract machine209) have state, as of the time the longjmp function was
called, except that the values of objects of automatic storage duration
that are local to the function containing the invocation of the
corresponding setjmp macro that do not have volatile-qualified type
and have been changed between the setjmp invocation and longjmp call are
indeterminate.
,---
| 209) This includes, but is not limited to, the floating-point status
| flags and the state of open files.
`---
Returns
4 After longjmp is completed, program execution continues as if the
corresponding invocation of the setjmp macro had just returned the value
specified by val. The longjmp function cannot cause the setjmp macro to
return the value 0; if val is 0, the setjmp macro returns the value 1.
5 EXAMPLE
The longjmp function that returns control back to the point of the
setjmp invocation might cause memory associated with a variable length
array object to be squandered.
#include <setjmp.h>
jmp_buf buf;
void g(int n);
void h(int n);
int n = 6;
void f(void)
{
int x[n]; // valid: f is not terminated
setjmp(buf);
g(n);
}
void g(int n)
{
int a[n]; // a may remain allocated
h(n);
}
void h(int n)
{
int b[n]; // b may remain allocated
longjmp(buf, 2); // might cause memory loss
}
--
E-Mail: Mine is an /at/ gmx /dot/ de address.
