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SubjectRe: strange gcc option, feature or bug?
On Fri, 17 May 1996, Y. Zhu wrote:

> Hi, all
> I found a strange gcc option problem, here is the Makefile:
>
> CC = gcc -O2
> objs = foo.o
> includedir =
> CCFLAGS = -Wall -fno-strength-reduce
> all: foo
> $(objs): %.o: %.c
> $(CC) -I$(includedir) -c $(CCFLAGS) $< -o $@
> foo: $(objs)
> $(CC) -o $@ $(objs)
>
> the problem is due to _includedir_ having a null string. This Makefile can
> produce at least two weird results according to the position of -Idir
> option:
>
> 1. just like above Makefile, it makes error message:
>
> gcc -O2 -I -c -Wall -fno-strength-reduce foo.c -o foo.o
This just means, that gcc should add -c to the include directories. (-c
is a legal Unix filename!)
> foo.c: In function `main':
> foo.c:5: warning: unused variable `i'
> gcc -O2 -o foo foo.o
> foo.o(.data+0x0): multiple definition of `__environ'
> /usr/lib/crt1.o(.data+0x0): first defined here
> foo.o: In function `_init':
> foo.o(.init+0x0): multiple definition of `_init'
> /usr/lib/crti.o(.init+0x0): first defined here
> foo.o: In function `_start':
> foo.o(.text+0x0): multiple definition of `_start'
> /usr/lib/crt1.o(.text+0x0): first defined here
> foo.o: In function `_start':
> foo.o(.text+0x0): multiple definition of `___crt_dummy__'
> /usr/lib/crt1.o(.text+0x0): first defined here
> foo.o: In function `_fini':
> foo.o(.fini+0x0): multiple definition of `_fini'
> /usr/lib/crti.o(.fini+0x0): first defined here
> /usr/lib/libc.so(.dynamic+0x0): multiple definition of `_DYNAMIC'
> /usr/lib/libc.so(.got.plt+0x0): multiple definition of `_GLOBAL_OFFSET_TABLE_'
> make: *** [foo] Error 1
Seems like you have severe linking problems :(
>
> 2. if I put the -Idir option behind the -c option, it seems override the
> next option -Wall, no warning!! but no error messages.
>
> gcc -O2 -c -I -Wall -fno-strength-reduce foo.c -o foo.o
Now this just means add -Wall to the include directories.
> gcc -O2 -o foo foo.o
>



It is a bit weird, but it isn't a bug :)

Andreas



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