[Bug c/45106] casting of variadic function pointers to normal function pointers causes segfaults on 64bit systems

[robert dot haschke at uni-bielefeld dot de]

--- Comment #1 from robert dot haschke at uni-bielefeld dot de  2010-07-28 
11:52 ---
Created an attachment (id=21335)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21335action=view)
preprocessed file


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45106

[Bug c/45106] casting of variadic function pointers to normal function pointers causes segfaults on 64bit systems

[robert dot haschke at uni-bielefeld dot de]

--- Comment #2 from robert dot haschke at uni-bielefeld dot de  2010-07-28 
11:53 ---
Created an attachment (id=21336)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21336action=view)
original .c file


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45106

[Bug c/45106] casting of variadic function pointers to normal function pointers causes segfaults on 64bit systems

[jakub at gcc dot gnu dot org]

--- Comment #3 from jakub at gcc dot gnu dot org  2010-07-28 11:57 ---
Don't do it, it is not valid.
The x86-64 ABI requires that for varargs the %al register contains number of
SSE regs that need saving, while for non-varargs functions that register is
undefined.


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jakub at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45106

[Bug c/45106] casting of variadic function pointers to normal function pointers causes segfaults on 64bit systems

[rhaschke at techfak dot uni-bielefeld dot de]

--- Comment #4 from rhaschke at techfak dot uni-bielefeld dot de  
2010-07-28 12:04 ---
Subject: Re:  casting of variadic function pointers to normal
 function pointers causes segfaults on 64bit systems

I was afraid of this answer.
However in my application, I have no clue which type of function pointer
is transferred. Thus, I should always cast to the variadic function
pointer in order to define the %al register?

Cheers, Robert


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45106

[Bug c/45106] casting of variadic function pointers to normal function pointers causes segfaults on 64bit systems

[schwab at linux-m68k dot org]

--- Comment #5 from schwab at linux-m68k dot org  2010-07-28 12:26 ---
Calling a function with a different signature than declared is undefined in any
case.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45106

[Bug c/45106] casting of variadic function pointers to normal function pointers causes segfaults on 64bit systems

[rguenth at gcc dot gnu dot org]

--- Comment #6 from rguenth at gcc dot gnu dot org  2010-07-28 14:01 ---
(In reply to comment #4)
 Subject: Re:  casting of variadic function pointers to normal
  function pointers causes segfaults on 64bit systems
 
 I was afraid of this answer.
 However in my application, I have no clue which type of function pointer
 is transferred. Thus, I should always cast to the variadic function
 pointer in order to define the %al register?
 
 Cheers, Robert

That doesn't work either.  You have to pass around some cookie that
tells you the function prototype and cast to the appropriate one.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45106