GCC-4.0.2 20050811: should GCC consider inlining functions in between different sections?

GCC-4.0.2 20050811: should GCC consider inlining functions in between different sections?

[Etienne Lorrain]

  Hello,

 Subject says it all - I do not know if that is new. I just have a bug
 in Gujin-1.2 with this new compiler, because function:

__attribute__ ((section (".xcode_start"), noreturn))
void xcodeseg_never_call_address_zero (void)

 calls xcodeseg_BOOT1_putstr() generated by macro:

#define GENERATE_VOID_EXTRA2CODE_INDIRECT_STUB(fctname, fctadr, params...) \
        __attribute__ ((section (STRING(.Xxcode2text_ ## fctname))))  \
        void xcodeseg_ ## fctname (params) {                            \
        EXTRASEG_REVERSE_STUB (fctadr, STRING(.Xtext2xcode_ ## fctname));\
        }

 Adding ", noinline" to the attribute list fix it all, I just was wondering
 if inlining in between GCC sections is safe in the general case.

  Etienne.



	

	
		
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Re: GCC-4.0.2 20050811: should GCC consider inlining functions in between different sections?

[Richard Guenther]

On 8/12/05, Etienne Lorrain <etienne_lorrain@yahoo.fr> wrote:
>   Hello,
> 
>  Subject says it all - I do not know if that is new. I just have a bug
>  in Gujin-1.2 with this new compiler, because function:
> 
> __attribute__ ((section (".xcode_start"), noreturn))
> void xcodeseg_never_call_address_zero (void)
> 
>  calls xcodeseg_BOOT1_putstr() generated by macro:
> 
> #define GENERATE_VOID_EXTRA2CODE_INDIRECT_STUB(fctname, fctadr, params...) \
>         __attribute__ ((section (STRING(.Xxcode2text_ ## fctname))))  \
>         void xcodeseg_ ## fctname (params) {                            \
>         EXTRASEG_REVERSE_STUB (fctadr, STRING(.Xtext2xcode_ ## fctname));\
>         }
> 
>  Adding ", noinline" to the attribute list fix it all, I just was wondering
>  if inlining in between GCC sections is safe in the general case.

Please explain the problem you're seeing.  I can see nothing wrong with inlining
functions within different sections in general.  If you're trying to
do things behind
the compilers back, though, be prepared to change workarounds with compiler
versions.

Richard.

Re: GCC-4.0.2 20050811: should GCC consider inlining functions in between different sections?

[Etienne Lorrain]

--- Richard Guenther <richard.guenther@gmail.com> wrote:
> Please explain the problem you're seeing.  I can see nothing wrong with
> inlining functions within different sections in general.  If you're
> trying to do things behind the compilers back, though, be prepared to
> change workarounds with compiler versions.

  For my project, i.e. Gujin on sourceforge, I am putting some sections
 in one place, some other in another place, and the relation in between
 sections has to be tightly controlled. For instance in Gujin, section
 names decides on which i386 code segment the code will be put - so that
 if you want to reference some symbols in another code section you have
 to do the equivalent of a far code instead of a near call.

  I have added a command to the linker file to forbid reference from
 one section to another:
NOCROSSREFS (.text .xcode);
 so that I can catch the unexpected use at link time. The inter-segment
 references have to be in some special sections - using some out-of-line
 functions.
 Inlining those special functions makes a symbol reference from a section
 name appear in another - in this special case my software would still
 work when the "NOCROSSREFS (.text .xcode);" is commented out.

  The question is in fact: what is a section for GCC? Is it just a way to
 group functions together to improve memory cache efficiency; or is the
 GCC user authorised to use sections to forbid access to some functions
 at link time?
  Is there a third use of sections I am not aware of? (excluding function
 sections for LD garbage collection of section, which is quite an
 orthogonal problem).

  Thanks for information,
  Etienne.


	

	
		
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Re: GCC-4.0.2 20050811: should GCC consider inlining functions in between different sections?

[Mike Stump]

On Aug 12, 2005, at 5:05 AM, Etienne Lorrain wrote:
>   I have added a command to the linker file to forbid reference from
>  one section to another:
> NOCROSSREFS (.text .xcode);

It sounds like this feature isn't compatible with inlining, -fno- 
inline I suspect is one of the few ways to `fix' it in general, that,  
or require that all functions be marked noinline that would otherwise  
be wrong to inline.

>   The question is in fact: what is a section for GCC?

Anything a user wants.  We don't limit the uses, so this question  
cannot, in general be answered, at best a few users could tell you  
how a few of them are using sections.  For example, I would not  
expect most people to know about NOCROSSREFS.

Re: GCC-4.0.2 20050811: should GCC consider inlining functions in between different sections?

[Jan Hubicka]

> On Aug 12, 2005, at 5:05 AM, Etienne Lorrain wrote:
> >  I have added a command to the linker file to forbid reference from
> > one section to another:
> >NOCROSSREFS (.text .xcode);
> 
> It sounds like this feature isn't compatible with inlining, -fno- 
> inline I suspect is one of the few ways to `fix' it in general, that,  
-fno-inline still won't suppress inlining of functions called once...

Honza
> or require that all functions be marked noinline that would otherwise  
> be wrong to inline.
> 
> >  The question is in fact: what is a section for GCC?
> 
> Anything a user wants.  We don't limit the uses, so this question  
> cannot, in general be answered, at best a few users could tell you  
> how a few of them are using sections.  For example, I would not  
> expect most people to know about NOCROSSREFS.

Re: GCC-4.0.2 20050811: should GCC consider inlining functions in between different sections?

[Segher Boessenkool]

>   The question is in fact: what is a section for GCC? Is it just a way 
> to
>  group functions together to improve memory cache efficiency; or is the
>  GCC user authorised to use sections to forbid access to some functions
>  at link time?

For user-declared ("attribute") sections, GCC just outputs
the necessary assembler magic, and that's it.  Anything else
is handled by your binary format tools, if at all.


Segher