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Mail Archives: djgpp/2004/08/10/21:00:41

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From: Brian Inglis <Brian DOT Inglis AT SystematicSw DOT Invalid>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Environment Variables
Organization: Systematic Software
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Date: Wed, 11 Aug 2004 00:49:00 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

On 10 Aug 2004 13:18:28 +0300 in comp.os.msdos.djgpp, Esa A E Peuha
<esa DOT peuha AT helsinki DOT fi> wrote:

>Brian Inglis <Brian DOT Inglis AT SystematicSw DOT Invalid> writes:
>
>> FWIW below is a list of library symbols that pollute the user global
>> namespace in *ALL* C programs and are not mentioned in the libc
>> documentation.
>
>Actually, most of them don't pollute the namespace at all.
>
>> It was produced by compiling and linking a small dummy program, then
>> running nm -Cg, stripping the addresses, and editing out the
>> documented names. 
>
>Giving the -C switch to nm is a bad idea, because you need the leading
>underscores to know if a symbol can pollute the namespace; those with no
>underscores don't pollute because they are inacessible from C, those
>with more than one don't pollute because they are reserved to the
>library.  Only the symbols with exactly one leading underscore can
>pollute, and not even all of those do.
>
>> The first letter tells you whether it's defined in a text, data or bss
>> segment. 
>> 
>> D djgpp_first_ctor
>> D djgpp_first_dtor
>> D djgpp_last_ctor
>> D djgpp_last_dtor
>> D edata
>> B end
>> B environ
>> T etext
>> B exception_stack
>> T start

Looks like you're correct about -Cg not being entirely truthful about
globals without leading _. The revised list of non-Standard globals
from a dummy program with no #includes compiled with -ansi -pedantic
are: 

T _close	close	*
D _edata	edata
B _end		end
B _environ	environ
T _etext	etext
T _sbrk		sbrk	*

where the routines marked * are Unix compatible routines called by the
startup/exit code. Can be worked around, as you indicate below? 
So djgpp_*, exception_stack, and start do not pollute, as you said. 

>Of these, the only one that does pollute at all is environ.
>
>> ISTM that a reasonable first step would be to document the existence
>> of these symbols in the libc documentation, and possibly add useful
>> public interfaces to some header file, perhaps only for the case of
>> environ, which seems to be the only symbol likely to be accessed by
>> user level code. 
>
>No, the reasonable first step is to fix it, since it's very easy to do.
>I'll post the fix to the djgpp-workers list.

Eli Z pointed out that it must be available for POSIX compatible code
that requires it, but should not be present for ANSI compiles. 
I would be interested in how you can have it defined, if it is
declared, but not defined as a global, and have it not be defined if
it is already defined? 

-- 
Thanks. Take care, Brian Inglis 	Calgary, Alberta, Canada

Brian DOT Inglis AT CSi DOT com 	(Brian dot Inglis at SystematicSw dot ab dot ca)
    fake address		use address above to reply

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