hello everyone..
int fun()
{
/* anything */
}
int main(void)
{
fun();
}
in this program, when the control is transferred to function fun()..
the return address is pushed to the stack..
Is it possible to access this value..??
Aug 3 '08
62  2896 
Chris Dollin wrote:
Nick Keighley wrote:
>On 4 Aug, 22:30, CBFalconer <cbfalco...@yah oo.comwrote:
>>jt wrote:
>int fun() {
/* anything */
}
int main(void) {
fun();
}
in this program, when the control is transferred to function
fun().. the return address is pushed to the stack..
Is it possible to access this value..??
In a machine that can execute the standard C language, there is no
need for a stack. This makes it hard to access a return address
(of unknown form) stored in a non-existant stack.
but the information must be stored *somewhere* otherwise
the implementation wouldn't be able to return from the function.
Admittedly the implementaion is under no obligation to make
it available to the user.
In the program above, if the compiler chose to inline `fun`, the
"return address" would be "stored" by the implicit fall-through of
one instruction to the next [1].
As we have discussed before, not all C programs need an explicit
run-time stack data-structure.
At least programs making use of recursion do, as far as I can see, and I
doubt that any sane implementation is going to use different strategies
for both these cases.
Of those that do, that structure
need not correspond to the local hardware's notion of "stack",
if it has one. Even if it does, the implementation is under no
requirement of the C standard to expose that stack to C programs.
And even if it /does/, mere ability should not elicit reckless
employment. One can, after all, clean one's teeth with a
screwdriver.
[1] On an implementation that uses "instructio ns", of course.
"Nick Keighley" <ni************ ******@hotmail. comwrote in message
news:57******** *************** ***********@a1g 2000hsb.googleg roups.com...
On 4 Aug, 23:25, Harald van D©¦k <true...@gmail. comwrote:
>On Mon, 04 Aug 2008 17:42:31 -0400, CBFalconer wrote:
Harold Aptroot wrote:
"MisterE" <Mist...@nimga. comwrote in message
>>>Is it possible to access [the return address] value..??
>>No.
>Of course it is. The OP did not request a standard compliant way to
do
it after all
On this newsgroup, there are no non-standard compliant ways to do
anything. Anything of that nature is off=topic,
Please don't use topicality as an excuse or defence for lies.
its not a lie. It's a fact. Your statement is incorrect. There
*is* no standard way to do this and since the topic of this NG
is standard C there is no way to do it that is topical to this
NG. Though I must admit I'd have suggested trying another NG.
So suppose someone asks here how to make coffee, we just tell him it's
completely impossible because the C standard has nothing to say on it?
>
>I don't know
if MisterE is aware of the existence of any non-portable methods of
accessing a function call's return address, but you are.
"jt" <ka**********@g mail.comwrote in message
news:38******** *************** ***********@v1g 2000pra.googleg roups.com...
hello everyone..
int fun()
{
/* anything */
}
int main(void)
{
fun();
}
in this program, when the control is transferred to function fun()..
the return address is pushed to the stack..
Is it possible to access this value..??
No problem, I thought, with a few lines of asm. But when I actually tried
it, it was quite difficult to pick up the return address.
On my machine, it depends on how many bytes of local variables there are in
a function. So this would require compiler help, or you have to tailor the
asm code to each function, and have it break as soon you change any
variables.
So whatever it is you're trying to do, best to think of a different way...
--
Bartc
Harold Aptroot wrote:
"Nick Keighley" <ni************ ******@hotmail. comwrote in message
news:57******** *************** ***********@a1g 2000hsb.googleg roups.com...
>On 4 Aug, 23:25, Harald van D?k <true...@gmail. comwrote:
>>On Mon, 04 Aug 2008 17:42:31 -0400, CBFalconer wrote:
Harold Aptroot wrote:
"MisterE" <Mist...@nimga. comwrote in message
>>>>Is it possible to access [the return address] value..??
No.
Of course it is. The OP did not request a standard compliant way
to do
it after all
On this newsgroup, there are no non-standard compliant ways to do
anything. Anything of that nature is off=topic,
Please don't use topicality as an excuse or defence for lies.
its not a lie. It's a fact. Your statement is incorrect. There
*is* no standard way to do this and since the topic of this NG
is standard C there is no way to do it that is topical to this
NG. Though I must admit I'd have suggested trying another NG.
So suppose someone asks here how to make coffee, we just tell him it's
completely impossible because the C standard has nothing to say on it?
No. We tell him that it's not possible to make coffee using *only*
Standard C, that system specific extensions will be necessary, and to
ask for more information in a group which deals with the system or
implementation the poster is using.
Harold Aptroot said:
<snip>
So suppose someone asks here how to make coffee, we just tell him it's
completely impossible because the C standard has nothing to say on it?
Forget better mousetraps. If you can demonstrate how to make coffee in ISO
C, the world will build a six-lane motorway to your door.
--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999
Bartc wrote:
>
"jt" <ka**********@g mail.comwrote in message
news:38******** *************** ***********@v1g 2000pra.googleg roups.com...
>hello everyone..
int fun()
{
/* anything */
}
int main(void)
{
fun();
}
in this program, when the control is transferred to function fun()..
the return address is pushed to the stack..
Is it possible to access this value..??
No problem, I thought, with a few lines of asm. But when I actually
tried it, it was quite difficult to pick up the return address.
On my machine, it depends on how many bytes of local variables there
are in a function. So this would require compiler help, or you have to
tailor the asm code to each function, and have it break as soon you
change any variables.
So whatever it is you're trying to do, best to think of a different
way...
I strongly suspect that all the compilers that the OP is likely to care
about provide a built-in for this purpose.
"santosh" <sa*********@gm ail.comwrote in message
news:g7******** **@registered.m otzarella.org.. .
Harold Aptroot wrote:
>"Nick Keighley" <ni************ ******@hotmail. comwrote in message
news:57******** *************** ***********@a1g 2000hsb.googleg roups.com...
>>On 4 Aug, 23:25, Harald van D?k <true...@gmail. comwrote:
On Mon, 04 Aug 2008 17:42:31 -0400, CBFalconer wrote:
Harold Aptroot wrote:
"MisterE" <Mist...@nimga. comwrote in message
>Is it possible to access [the return address] value..??
No.
Of course it is. The OP did not request a standard compliant way
to do
it after all
On this newsgroup, there are no non-standard compliant ways to do
anything. Anything of that nature is off=topic,
Please don't use topicality as an excuse or defence for lies.
its not a lie. It's a fact. Your statement is incorrect. There
*is* no standard way to do this and since the topic of this NG
is standard C there is no way to do it that is topical to this
NG. Though I must admit I'd have suggested trying another NG.
So suppose someone asks here how to make coffee, we just tell him it's
completely impossible because the C standard has nothing to say on it?
No. We tell him that it's not possible to make coffee using *only*
Standard C, that system specific extensions will be necessary, and to
ask for more information in a group which deals with the system or
implementation the poster is using.
See? Now that's different than MisterE's plain "no"
Harold Aptroot wrote:
"santosh" <sa*********@gm ail.comwrote in message
news:g7******** **@registered.m otzarella.org.. .
>Harold Aptroot wrote:
>>>>"MisterE" <Mist...@nimga. comwrote in message
>>Is it possible to access [the return address] value..??
>
>No.
>>So suppose someone asks here how to make coffee, we just tell him
it's completely impossible because the C standard has nothing to say
on it?
No. We tell him that it's not possible to make coffee using *only*
Standard C, that system specific extensions will be necessary, and to
ask for more information in a group which deals with the system or
implementati on the poster is using.
See? Now that's different than MisterE's plain "no"
If "MisterE" meant his "No" as specifically within the context of ISO C,
then he is factually correct, though a more verbose, explanatory
response would've perhaps been better, but many such responses were
already provided to the OP by the time MisterE's post showed up on my
newsserver.
santosh wrote:
Chris Dollin wrote:
>As we have discussed before, not all C programs need an explicit
run-time stack data-structure.
At least programs making use of recursion do, as far as I can see,
Not all programs that make use of recursion need an explicit run-time
stack, either. But yes, programs (or parts thereof) that do non-tail
recursion will need /something/ like a run-time stack.
and I
doubt that any sane implementation is going to use different strategies
for both these cases.
Whole-program compilation might well choose to, if that was more
efficient. Suppose one were making a serious attempt to compile
as-Standard-as-possible C programs for the 6502, where stack depth
/really/ matters. Or the PDP8, which has the added delightful
feature that the subroutine return address gets planted /at the
target of the call instruction/.
I don't know if today's embedded processors are equally jabberwock-laden,
(except that the ARM isn't), but I'd lay odds that on at least some of
them, if essential recursion is allowed at all, the compiler will
treat recursive (or re-entrant) functions differently from non-R
functions.
--
'It changed the future .. and it changed us.' /Babylon 5/
Hewlett-Packard Limited registered no:
registered office: Cain Road, Bracknell, Berks RG12 1HN 690597 England
Chris Dollin wrote:
I don't know if today's embedded processors are equally jabberwock-laden,
(except that the ARM isn't), but I'd lay odds that on at least some of
them, if essential recursion is allowed at all, the compiler will
treat recursive (or re-entrant) functions differently from non-R
functions.
For "will treat" safer to read "will treat, or can be told to treat".
--
'It changed the future .. and it changed us.' /Babylon 5/
Hewlett-Packard Limited registered no:
registered office: Cain Road, Bracknell, Berks RG12 1HN 690597 England This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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