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Re: Preprocessing oddity breaks binutils


On Wed, 02 Jun 1999 12:04:06 -0400, Dave Brolley wrote:
>I agree that this is probably a long standing quirk bug in the
>preprocessor which is arguably a bug. Does anyone know of any source which
>relies on the current behaviour?

FYI, cpplib uses the test.h in the subdirectory.  I agree with Mark that
this is the right thing - #line should not affect the search path.

zw

>
>Dave
>
>Mark Mitchell wrote:
>
>> It's impossible to build the current binutils in CVS because of what I
>> think is a bug in the C preprocessor.  Consider the following
>> directory layout:
>>
>>   linux1.codesourcery.com% ls -lR
>>   total 2
>>   drwxrwx--x   2 mitchell mitchell     1024 Jun  1 18:54 baz/
>>   -rw-rw----   1 mitchell mitchell        7 Jun  1 18:49 test.h
>>
>>   baz:
>>   total 1
>>   -rw-rw----   1 mitchell mitchell       38 Jun  1 18:50 test.c
>>   -rw-rw----   1 mitchell mitchell        0 Jun  1 18:49 test.h
>>
>> Suppose that baz/test.h is empty, but that the top-level baz.h
>> contains a #error.  Suppose that test.c is:
>>
>>   #line 1 "../test.c"
>>   #include "test.h"
>>
>> Now, suppose that in baz you run:
>>
>>   cpp test.c
>>
>> What happens is:
>>
>>   linux1.codesourcery.com% cpp test.c
>>   In file included from ../test.c:1:
>>   ../test.h:1: #error
>>
>> The standards are pretty obscure about what exactly a #line does, or
>> for that matter, how the include path is searched, but I think this is
>> very confusing behavior.  I would never guess, as a user, that what
>> #lines are inserted in a source file would affect where we would
>> search for the file.
>>
>> In the binutils case, what's happening is that a generated lexer (from
>> lex) is being placed in the objdir, along with a a generated include
>> file full of tokens.  However, there's *already* a file of tokens in
>> srcdir.  When compiling the lexer, we get the old file of tokens,
>> because the lexer contains #line directives referring back to the old
>> lexer.
>>
>> Perhaps, in the interests of portability, some kind of modification to
>> binutils or automake is a good idea as well.  (This is happenning with
>> ldlex.l, ldgram.h, and friends in the `ld' subdirectory of binutils.)
>>
>> --
>> Mark Mitchell                   mark@codesourcery.com
>> CodeSourcery, LLC               http://www.codesourcery.com
>
>
>

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