Output sections

Output sections

[Mohamed Shafi]

Hello all,

Is it possible to emit a assembler directive at the end of each sections?
Say like section_end
Is there any support for doing something like this in the back-end files?
Or should i need to the make changes in the gcc sources?
Is so do does anyone know in which function it should happen?

Regards,
Shafi

Re: Output sections

[Dave Korn]

Mohamed Shafi wrote:
> Hello all,
> 
> Is it possible to emit a assembler directive at the end of each sections?
> Say like section_end
> Is there any support for doing something like this in the back-end files?
> Or should i need to the make changes in the gcc sources?
> Is so do does anyone know in which function it should happen?

  There isn't really such a concept as 'end of a section' until you get to
final-link time and get all the contributions from different .o files to a
given section.  During assembler output GCC treats sections as random access,
switching freely from one to another and back; it doesn't have any concept of
starting/stopping/opening/closing a section but just jumps into any one it
likes completely ad-hoc.

  Assuming you're happy with adding something to the end of each section in
each generated .s file, you could use the TARGET_ASM_FILE_END hook to output
directives that re-enter each used section and then output your new directive.
 You may find it hard to know which sections have been used or not in a given
file - you can define TARGET_ASM_NAMED_SECTION and make a note of which
sections get invoked there, but I'm not sure if that gets called for all
sections e.g. init/fini, you may have to try it and see.

    cheers,
      DaveK

Re: Output sections

[Mohamed Shafi]

2009/7/18 Dave Korn <dave.korn.cygwin@googlemail.com>:
> Mohamed Shafi wrote:
>> Hello all,
>>
>> Is it possible to emit a assembler directive at the end of each sections?
>> Say like section_end
>> Is there any support for doing something like this in the back-end files?
>> Or should i need to the make changes in the gcc sources?
>> Is so do does anyone know in which function it should happen?
>
>  There isn't really such a concept as 'end of a section' until you get to
> final-link time and get all the contributions from different .o files to a
> given section.  During assembler output GCC treats sections as random access,
> switching freely from one to another and back; it doesn't have any concept of
> starting/stopping/opening/closing a section but just jumps into any one it
> likes completely ad-hoc.
>
>  Assuming you're happy with adding something to the end of each section in
> each generated .s file, you could use the TARGET_ASM_FILE_END hook to output
> directives that re-enter each used section and then output your new directive.
>  You may find it hard to know which sections have been used or not in a given
> file - you can define TARGET_ASM_NAMED_SECTION and make a note of which
> sections get invoked there, but I'm not sure if that gets called for all
> sections e.g. init/fini, you may have to try it and see.
>

I am looking for adding something to the end of each section in the
generated .s file. Using TARGET_ASM_NAMED_SECTION i will be able to
keep track of the sections that are being emitted. But from
TARGET_ASM_FILE_END hook how can i re-enter into each section. Are the
sections stored in some global variable?

Shafi

Re: Output sections

[Dave Korn]

Mohamed Shafi wrote:
> I am looking for adding something to the end of each section in the
> generated .s file. Using TARGET_ASM_NAMED_SECTION i will be able to
> keep track of the sections that are being emitted. But from
> TARGET_ASM_FILE_END hook how can i re-enter into each section. Are the
> sections stored in some global variable?

  I'm not sure I understand the question.  You "enter a section" simply by
emitting the correct .section directive into the asm output.  You re-enter it by
the same method.

    cheers,
      DaveK

Re: Output sections

[Mohamed Shafi]

2009/8/1 Dave Korn <dave.korn.cygwin@googlemail.com>:
> Mohamed Shafi wrote:
>> I am looking for adding something to the end of each section in the
>> generated .s file. Using TARGET_ASM_NAMED_SECTION i will be able to
>> keep track of the sections that are being emitted. But from
>> TARGET_ASM_FILE_END hook how can i re-enter into each section. Are the
>> sections stored in some global variable?
>
>  I'm not sure I understand the question.  You "enter a section" simply by
> emitting the correct .section directive into the asm output.  You re-enter it by
> the same method.
>
>    cheers,
>      DaveK
>

Ok, Then i don't understand your solution.

>> you could use the TARGET_ASM_FILE_END hook to output
>> directives that re-enter each used section and then output your new directive.

if i want to do the following in the assembly output

section .code
.....
.....
......
section_end


you are saying that if i emit a section directive the compiler will
switch to the previously emitted section and then i have to somehow
seek to the end of that section and emit my 'section_end' directive?

Shafi

Re: Output sections

[Dave Korn]

Mohamed Shafi wrote:
> 2009/8/1 Dave Korn <dave.korn.cygwin@googlemail.com>:
>> Mohamed Shafi wrote:
>>> I am looking for adding something to the end of each section in the
>>> generated .s file. Using TARGET_ASM_NAMED_SECTION i will be able to
>>> keep track of the sections that are being emitted. But from
>>> TARGET_ASM_FILE_END hook how can i re-enter into each section. Are the
>>> sections stored in some global variable?
>>  I'm not sure I understand the question.  You "enter a section" simply by
>> emitting the correct .section directive into the asm output.  You re-enter it by
>> the same method.

> Ok, Then i don't understand your solution.

  Ah, it looks like I didn't quite understand your problem.

>>> you could use the TARGET_ASM_FILE_END hook to output
>>> directives that re-enter each used section and then output your new directive.
> 
> if i want to do the following in the assembly output
> 
> section .code
> .....
> .....
> ......
> section_end

  I thought you just wanted to have

   .section .code
   section_end
   .section .data
   section_end

... etc. for all used sections, at the very end of the file; after all, all the
contributions to a section get concatenated in the assembler.  Now you seem to
be saying that you want to have multiple section_end directives throughout the
file, every time the current section changes.

> you are saying that if i emit a section directive the compiler will
> switch to the previously emitted section and then i have to somehow
> seek to the end of that section and emit my 'section_end' directive?

  I think you may need to re-read the assembler manual about sections, you are a
little confused about the concepts.  The compiler doesn't really "switch"
anything; the compiler emits ".section" directives, in response to which the
*assembler* switches to emit code in the chosen section.  The compiler doesn't
keep track of sections; it just randomly emits directives for whichever one it
wants the assembly output to go into at any given time, according to whether
it's generating the assembly for a function or a variable or other data object.

    cheers,
      DaveK

Re: Output sections

[Mohamed Shafi]

2009/8/1 Dave Korn <dave.korn.cygwin@googlemail.com>:
> Mohamed Shafi wrote:
>> 2009/8/1 Dave Korn <dave.korn.cygwin@googlemail.com>:
>>> Mohamed Shafi wrote:
>>>> I am looking for adding something to the end of each section in the
>>>> generated .s file. Using TARGET_ASM_NAMED_SECTION i will be able to
>>>> keep track of the sections that are being emitted. But from
>>>> TARGET_ASM_FILE_END hook how can i re-enter into each section. Are the
>>>> sections stored in some global variable?
>>>  I'm not sure I understand the question.  You "enter a section" simply by
>>> emitting the correct .section directive into the asm output.  You re-enter it by
>>> the same method.
>
>> Ok, Then i don't understand your solution.
>
>  Ah, it looks like I didn't quite understand your problem.
>
>>>> you could use the TARGET_ASM_FILE_END hook to output
>>>> directives that re-enter each used section and then output your new directive.
>>
>> if i want to do the following in the assembly output
>>
>> section .code
>> .....
>> .....
>> ......
>> section_end
>
>  I thought you just wanted to have
>
>   .section .code
>   section_end
>   .section .data
>   section_end
>
> ... etc. for all used sections, at the very end of the file; after all, all the
> contributions to a section get concatenated in the assembler.  Now you seem to
> be saying that you want to have multiple section_end directives throughout the
> file, every time the current section changes.
>
>> you are saying that if i emit a section directive the compiler will
>> switch to the previously emitted section and then i have to somehow
>> seek to the end of that section and emit my 'section_end' directive?
>
>  I think you may need to re-read the assembler manual about sections, you are a
> little confused about the concepts.  The compiler doesn't really "switch"
> anything; the compiler emits ".section" directives, in response to which the
> *assembler* switches to emit code in the chosen section.  The compiler doesn't
> keep track of sections; it just randomly emits directives for whichever one it
> wants the assembly output to go into at any given time, according to whether
> it's generating the assembly for a function or a variable or other data object.
>

Ok. will TARGET_NAMED_SECTION get invoked for the normal sections like
text, data, bss ? I tired to include this hook in my code, but the
execution never reaches this hook for the sections.

Shafi