From:	"Andrew Crabtree" <andrew_crabtree AT hp DOT com>
To:	<djgpp-workers AT delorie DOT com>
Subject:	RE: COFF format
Date:	Thu, 25 Feb 1999 16:28:48 -0800
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> 1) what's in eh_frame section ? (can I simply and silently ignore it ?)
I believe the eh stuff is exception handling.  Maybe frame unwind info?  Can
probably get a better feel for what goes in there if you peruse the gcc
macros for x86 target.

> 2) why non-static uninitialized global objects appear as "undefined" ?
Well, it has to do with how the linker collapses things.  I'm assuming you
are talking about a .o file here, and not a finished executable.  The
problem is that your declaration

char arr[1000];

is the same as

extern char arr[1000];

as far as it knows.  So when its looking at that one particular file it
doesn't know if it needs to reserve bss space for an unitialized global or
if the variable is declared somewhere else.  The final linker figures things
out.  Some other fancier formats (ELF for instance) take better care of
this.  I think gld has an option of warn-common or something if you happen
to make two globals the same name and one is explicit and one isn't.  Does
that make sense?  Here's two examples to clear it up a little more.

lets say you have one file, main.c.  In it you have

char arr[1000];

When you compile to a .o it fill make an unresolved external.   When you
make the .out or .exe the linker will know to reserve space for it.  But,
lets say you have this scenario.
You have a main.c in which again you have

char arr[1000];

but you have another file file2.c in which you have

char arr[1000] = {0,1,2,3,4,5,...};

or something similar.  The same thing happens to main.c when it is compiled
to main.o, but this time the linker resolve arr to point into file2, which
may or may not be what you wanted it to do.  Its a throw back to old k&r
days where nobody used the 'extern' keyword I would guess.

> Is there some doc that explains that format ?
No idea.

HTH  andy

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