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From: j@bonnie.heep.sax.de (J Wunsch)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: When did this become linux.advocacy
Date: 29 Jun 1995 11:20:25 +0200
Organization: Private U**x site, Dresden.
Lines: 92
Message-ID: <3str8p$akq@bonnie.tcd-dresden.de>
References: <marcus.114.00E9749F@ccelab.iastate.edu> <3shime$l2i@news.nynexst.com> <DAt15p.F5p@citylink.dinoex.sub.org> <3ss3fh$ig7@agate.berkeley.edu>
Reply-To: joerg_wunsch@uriah.heep.sax.de
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While i cannot comment on the other problems, allow me a note on
this:
Nick Kralevich <nickkral@octans.EECS.Berkeley.EDU> wrote:
>>3. cc/ld is no longer able to handle certain global variable names. The
>> programs will be built without error-message, but will crash with
>> segfault, when the global variable is written the first time. [...]
>I would claim that you didn't find anything because #3 isn't a common
>problem. I've never had any problem compiling programs that use
>global variables. If this is a bug, then it is a bug with GNU gcc,
>and I suggest you report it to them.
It's a common misconception of several C cc/ld systems (not only gcc)
that the linker doesn't complain about multiply defined symbols in the
sections text and bss. Hence some module might try to reference a
variable ``foo'', while another module is going to define ``foo'' to
be a function. The result is great confusion. Below an example:
j@bonnie 141% uname -sr
FreeBSD 1.1.5.1(RELEASE)
j@bonnie 142% cat foo.c
#include <stdio.h>
void foo(void)
{
printf("This is foo\n");
}
void bar(void)
{
foo();
}
j@bonnie 143% cat bar.c
#include <stdio.h>
extern void bar(void);
int foo;
int main(void)
{
foo++;
bar();
printf("This is another foo: %d\n", foo);
return 0;
}
j@bonnie 144% cc -o foo foo.c bar.c
j@bonnie 145% ./foo
Bus error (core dumped)
j@mara 62% uname -sr
dgux 5.4R3.00
j@mara 63% cc -o foo foo.c bar.c
foo.c:
bar.c:
ld: bar.o: warning: symbol: `foo` has different size in file foo.o
ld: bar.o: warning: incompatible types for symbol: `foo` also in file foo.o
j@mara 64% ./foo
Segmentation fault (core dumped)
j@mara 65% setenv TARGET_BINARY_INTERFACE m88kdguxcoff
j@mara 66% cc -o foo foo.c bar.c
foo.c:
bar.c:
j@mara 67% ./foo
Bus error (core dumped)
j@pluto 60% uname -sr
IRIX 5.2
j@pluto 61% cc -o foo foo.c bar.c
foo.c:
bar.c:
ld:
Warning: bar.o: foo: multiply defined
previous (used) definition from 'foo.o';
new (ignored) definition from 'bar.o'
j@pluto 62% ./foo
Segmentation fault (core dumped)
As you can see, DG/UX in the default (ELF) environment and Irix got it
(almost) right in issuing a warning (while it's actually an error).
DG/UX in the COFF environment fails as FreeBSD does. I guess Linux
would behave as FreeBSD here, since both are essentially using the
same compiler/loader. (Perhaps Linux would do the Right Thing in ELF,
too?)
--
cheers, J"org private: joerg_wunsch@uriah.heep.sax.de
http://www.sax.de/~joerg/
Never trust an operating system you don't have sources for. ;-)