Exception handling crashes or exits

[Fabiano Sidler]

Hi folks!

I'm using gcc 4.2.3 and glibc6 2.7.
I'm doing an exception handling implementation for a library. Although I
assume to have it done properly, with a handler set up, it exits the program
with a random exit value, and without a handler set up, it crashes with a
SIGSEGV, but as I have found out with gdb, at the same line of code:

__libc_siglongj mp (env=0xbfb935f0 , val=1) at longjmp.c:29
29 {
31 _longjmp_unwind (env, val);
_longjmp_unwind (env=0xbfb935f0 , val=1) at
../nptl/sysdeps/unix/sysv/linux/jmp-unwind.c:32
32 if (__libc_pthread _functions_init )
39 }
__libc_siglongj mp (env=0xbfb935f0 , val=1) at longjmp.c:33
33 if (env[0].__mask_was_sav ed)
39 __longjmp (env[0].__jmpbuf, val ?: 1);
The types i use are:

typedef struct ExcType ExcType;
typedef struct ExcVal ExcVal;
typedef struct Exception Exception;
struct ExcType {
const char *name;
};
union ExcVal {
void* None;
int Int;
char* Char;
};
typedef enum {
NoneType,
IntType,
CharType
} Datatype;
struct Exception {
ExcType *tp;
ExcVal *val;
Datatype dt;
};
struct ExcEntry {
ExcEntry *prev,*next;
jmp_buf buf;
Exception *exc;
};
extern ExcEntry *currexc;
My macros for doing exception handling are as follows:

#define try \
{\
Exception exc;\
ExcEntry excn;\
excn.exc=&exc; excn.prev=curre xc;\
currexc = excn.prev->next = &excn;\
if ( setjmp(excn.buf )==0 )
#define catch(e) \
Exception *e = &exc;\
for (;0;currexc=cur rexc->prev)
#define exctype(et, action) \
if ( e->tp==&et ) { action; }
#define endtry }
#define throw(t,vl) \
{currexc->exc->tp=NULL;\
currexc->exc->tp=&t;\
currexc->exc->val->Char=(char*)vl ;\
currexc->exc->dt=CharType; \
jmp_buf buf;\
memcpy((void*)& buf,(void*)curr exc->buf, sizeof(jmp_buf) );\
longjmp(buf,1); }
A sample program could be:

#include <stdio.h>
ExcType RuntimeError;
int main(int argc, char **argv)
{
try {
throw(RuntimeEr ror,"test error");
} catch(e) {
fprintf(stderr, "foobar!\n" );
exit(42);
} endtry;
}
I don't see where the problem is. Any professional here who can help me?

Greetings,
Fabiano

[Andrew Poelstra]

On 2008-09-08, Fabiano Sidler <fa***********@ my-mail.chwrote:

Hi folks!

I'm using gcc 4.2.3 and glibc6 2.7.
I'm doing an exception handling implementation for a library. Although I
assume to have it done properly, with a handler set up, it exits the program
with a random exit value, and without a handler set up, it crashes with a
SIGSEGV, but as I have found out with gdb, at the same line of code:

__libc_siglongj mp (env=0xbfb935f0 , val=1) at longjmp.c:29
29 {
31 _longjmp_unwind (env, val);
_longjmp_unwind (env=0xbfb935f0 , val=1) at
../nptl/sysdeps/unix/sysv/linux/jmp-unwind.c:32
32 if (__libc_pthread _functions_init )
39 }
__libc_siglongj mp (env=0xbfb935f0 , val=1) at longjmp.c:33
33 if (env[0].__mask_was_sav ed)
39 __longjmp (env[0].__jmpbuf, val ?: 1);
The types i use are:

typedef struct ExcType ExcType;
typedef struct ExcVal ExcVal;
typedef struct Exception Exception;
struct ExcType {
const char *name;
};
union ExcVal {
void* None;
int Int;
char* Char;
};
typedef enum {
NoneType,
IntType,
CharType
} Datatype;
struct Exception {
ExcType *tp;
ExcVal *val;
Datatype dt;
};
struct ExcEntry {
ExcEntry *prev,*next;
jmp_buf buf;
Exception *exc;
};
extern ExcEntry *currexc;

Where is this defined? You appear to use it without ever
defining it. Does this program link successfully?

>
My macros for doing exception handling are as follows:

#define try \
{\
Exception exc;\
ExcEntry excn;\
excn.exc=&exc; excn.prev=curre xc;\
currexc = excn.prev->next = &excn;\
if ( setjmp(excn.buf )==0 )
#define catch(e) \
Exception *e = &exc;\
for (;0;currexc=cur rexc->prev)
#define exctype(et, action) \
if ( e->tp==&et ) { action; }
#define endtry }
#define throw(t,vl) \
{currexc->exc->tp=NULL;\
currexc->exc->tp=&t;\
currexc->exc->val->Char=(char*)vl ;\
currexc->exc->dt=CharType; \
jmp_buf buf;\
memcpy((void*)& buf,(void*)curr exc->buf, sizeof(jmp_buf) );\
longjmp(buf,1); }
A sample program could be:

#include <stdio.h>
ExcType RuntimeError;
int main(int argc, char **argv)
{
try {
throw(RuntimeEr ror,"test error");
} catch(e) {
fprintf(stderr, "foobar!\n" );
exit(42);
} endtry;
}
I don't see where the problem is. Any professional here who can help me?

Greetings,
Fabiano

--
Andrew Poelstra ap*******@wpsof tware.com
To email me, use the above email addresss with .com set to .net

[Fabiano Sidler]

On 2008-09-08, Andrew Poelstra <ap*******@supe rnova.homewrote :

Where is this defined?

jmp_buf is defined in setjmp.h which is, in turn, an ANSI C header.
Maybe i should have written this...in my program, it is included.

Does this program link successfully?

<setjmp.hmust be included and the definitions (and the declaration)
must be done before main(), but then it does, otherwise it couldn't SEGSEGV
here...;)

Greetings,
Fabiano

[Andrew Poelstra]

On 2008-09-08, Fabiano Sidler <fa***********@ my-mail.chwrote:

On 2008-09-08, Andrew Poelstra <ap*******@supe rnova.homewrote :

>Where is this defined?

jmp_buf is defined in setjmp.h which is, in turn, an ANSI C header.
Maybe i should have written this...in my program, it is included.

Sure, but jmp_buf is just a member of the currexc object, for
which storage is never allocated (since this object is not
defined, as far as I can tell).

>Does this program link successfully?

<setjmp.hmus t be included and the definitions (and the declaration)
must be done before main(), but then it does, otherwise it couldn't SEGSEGV
here...;)

--
Andrew Poelstra ap*******@wpsof tware.com
To email me, use the above email addresss with .com set to .net

[Keith Thompson]

Andrew Poelstra <ap*******@supe rnova.homewrite s:

On 2008-09-08, Fabiano Sidler <fa***********@ my-mail.chwrote:

>On 2008-09-08, Andrew Poelstra <ap*******@supe rnova.homewrote :

>>Where is this defined?

jmp_buf is defined in setjmp.h which is, in turn, an ANSI C header.
Maybe i should have written this...in my program, it is included.

Sure, but jmp_buf is just a member of the currexc object, for
which storage is never allocated (since this object is not
defined, as far as I can tell).

Here's the relevant code from the original article:
| struct ExcEntry {
| ExcEntry *prev,*next;
| jmp_buf buf;
| Exception *exc;
| };
| extern ExcEntry *currexc;

jmp_buf is a type, declared in the standard header <setjmp.h>. The
point is simply that you can't refer to the name "jmp_buf" unless you
have a "#include <setjmp.h>".

buf, on the other hand, is a member of the type struct ExcEntry; that
member is of type jmp_buf. And currexc is a pointer to struct
ExcEntry. So buf (not jmp_buf) is a member of *currexc (not currexc).

[...]

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Andrew Poelstra]

On 2008-09-09, Keith Thompson <ks***@mib.orgw rote:

Andrew Poelstra <ap*******@supe rnova.homewrite s:

>On 2008-09-08, Fabiano Sidler <fa***********@ my-mail.chwrote:

>>On 2008-09-08, Andrew Poelstra <ap*******@supe rnova.homewrote :
Where is this defined?

jmp_buf is defined in setjmp.h which is, in turn, an ANSI C header.
Maybe i should have written this...in my program, it is included.

Sure, but jmp_buf is just a member of the currexc object, for
which storage is never allocated (since this object is not
defined, as far as I can tell).

Here's the relevant code from the original article:
| struct ExcEntry {
| ExcEntry *prev,*next;
| jmp_buf buf;
| Exception *exc;
| };
| extern ExcEntry *currexc;

jmp_buf is a type, declared in the standard header <setjmp.h>. The
point is simply that you can't refer to the name "jmp_buf" unless you
have a "#include <setjmp.h>".

buf, on the other hand, is a member of the type struct ExcEntry; that
member is of type jmp_buf. And currexc is a pointer to struct
ExcEntry. So buf (not jmp_buf) is a member of *currexc (not currexc).

[...]

But currexc is declared as extern and never defined, so when is
storage set aside for the pointer itself?

(But you are right, I missed that currexc was a pointer.)

--
Andrew Poelstra ap*******@wpsof tware.com
To email me, use the above email addresss with .com set to .net

[Peter Nilsson]

Fabiano Sidler <fabianosid...@ my-mail.chwrote:

I'm doing an exception handling implementation for a
library. ...

The types i use are:

typedef struct ExcType ExcType;
typedef struct ExcVal ExcVal;
typedef struct Exception Exception;
struct ExcType {
* * * * const char *name;};

union ExcVal {
* * * * void* None;
* * * * int Int;
* * * * char* Char;};

typedef enum {
* * * * NoneType,
* * * * IntType,
* * * * CharType} Datatype;

struct Exception {
* * * * ExcType *tp;
* * * * ExcVal *val;
* * * * Datatype dt;};

struct ExcEntry {
* * * * ExcEntry *prev,*next;
* * * * jmp_buf buf;
* * * * Exception *exc;};

extern ExcEntry *currexc;

My macros for doing exception handling are as follows:

#define try \
* * * * {\
* * * * * * * * Exception exc;\
* * * * * * * * ExcEntry excn;\
* * * * * * * * excn.exc=&exc; excn.prev=curre xc;\

Are you sure currexc is not a null pointer?

* * * * * * * * currexc = excn.prev->next = &excn;\

If it is, this line is problematic.

* * * * * * * * if ( setjmp(excn.buf )==0 )
#define catch(e) \
* * * * * * * * Exception *e = &exc;\

Seems to be missing an 'else' for the above 'if'. Also,
I prefer to insert the { } blocks directly (split across
the macros,) rather than relying on the user to supply
them.

* * * * * * * * for (;0;currexc=cur rexc->prev)
#define exctype(et, action) \
* * * * * * * * * * * * if ( e->tp==&et ) { action; }
#define endtry *}
#define throw(t,vl) \
* * * * {currexc->exc->tp=NULL;\
* * * * currexc->exc->tp=&t;\
* * * * currexc->exc->val->Char=(char*)vl ;\
* * * * currexc->exc->dt=CharType; \
* * * * jmp_buf buf;\
* * * * memcpy((void*)& buf,(void*)curr exc->buf, sizeof(jmp_buf) );\
* * * * longjmp(buf,1); }

A sample program could be:

#include <stdio.h>
ExcType RuntimeError;
int main(int argc, char **argv)
{
* * * * try {
* * * * * * * * throw(RuntimeEr ror,"test error");
* * * * } catch(e) {
* * * * * * * * fprintf(stderr, "foobar!\n" );
* * * * * * * * exit(42);
* * * * } endtry;

}

I don't see where the problem is. Any professional here who can help me?

Greetings,
Fabiano

[Fabiano Sidler]

I _do_ include setjmp.h, this is not the problem...i don't get errors
due to that, anyway! ;)

Greetings,
Fabiano

[Fabiano Sidler]

On 2008-09-09, Peter Nilsson <ai***@acay.com .auwrote:

Are you sure currexc is not a null pointer?

currexc is initialized as follows:

ExcEntry *currexc = &(ExcEntry) {
NULL,
NULL,
{0},
&(Exception) {
NULL,
&(ExcVal) { 0 },
0
}
};

And yes, this is valid C, C99! ;)
Your other points i'm working on right now...:)

Thanks in advance,
Fabiano

[Fabiano Sidler]

Here is the complete demo program:

--- snip ---
#include <stdio.h>
#include <setjmp.h>
#include <stdlib.h>
#include <string.h>

typedef struct ExcType ExcType;
typedef union ExcVal ExcVal;
typedef struct Exception Exception;
typedef struct ExcEntry ExcEntry;
struct ExcType {
const char *name;
};
union ExcVal {
void* None;
int Int;
char* Char;
};
typedef enum {
NoneType,
IntType,
CharType
} Datatype;
struct Exception {
ExcType *tp;
ExcVal *val;
Datatype dt;
};
struct ExcEntry {
ExcEntry *prev,*next;
jmp_buf buf;
Exception *exc;
};
ExcEntry *currexc = &(ExcEntry) {
NULL,
NULL,
{0},
&(Exception) {
NULL, &(ExcVal){0} , 0
}
};
#define try \
{\
Exception exc;\
ExcEntry excn;\
excn.exc=&exc; excn.prev=curre xc;\
currexc = excn.prev->next = &excn;\
if ( setjmp(excn.buf )==0 )
#define catch(e) \
Exception *e = &exc;\
for (;0;currexc=cur rexc->prev)
#define exctype(et, action) \
if ( e->tp==&et ) { action; }
#define endtry }
#define throw(t,vl) \
{currexc->exc->tp=NULL;\
currexc->exc->tp=&t;\
currexc->exc->val->Char=(char*)vl ;\
currexc->exc->dt=CharType; \
jmp_buf buf;\
memcpy((void*)& buf,(void*)curr exc->buf, sizeof(jmp_buf) );\
longjmp(buf,1); }

ExcType RuntimeError;

int main(int argc, char **argv)
{
try {
throw(RuntimeEr ror,"test error");
} catch(e) {
fprintf(stderr, "caught\n") ;
exit(0);
} endtry
fprintf(stderr, "uncaught\n ");
return 42;
}
--- snap ---

Greetings,
Fabiano