Bug 69439

The shebang is the first line in the source file, and in the output when I
run it here.   Perhaps you're using a cpp that's inserting extra blank lines?

http://cgit.freedesktop.org/xorg/app/xinit/tree/startx.cpp

To add to my previous post (sorry for forgetting this), the system is archlinux x86_64 with gcc 4.8.1.

(In reply to comment #1)
> The shebang is the first line in the source file, and in the output when I
> run it here.   Perhaps you're using a cpp that's inserting extra blank lines?
> 
> http://cgit.freedesktop.org/xorg/app/xinit/tree/startx.cpp

I see. Then it's an issue on the distro side -- I'll look closer at the cpp behavior.

Thanks.

I tested with Solaris cpp & gcc 4.7.3 on Solaris, so it could be a change
between gcc 4.7 & 4.8.

This also affects xmkmf and makedepend from imake. These projects use cpp to parse cpp files to shellscript.

Looking at the makefiles, this line is used to generate xmkmf:
/usr/bin/cpp -undef -traditional -DCONFIGDIRSPEC='"-I/usr/lib/X11/config"' < ./xmkmf.cpp | /usr/bin/sed -e /^\#/d | /usr/bin/sed -e s/XCOMM/\#/ > xmkmf

Changing it to:
/usr/bin/cpp -undef -traditional -DCONFIGDIRSPEC='"-I/usr/lib/X11/config"'  ./xmkmf.cpp | /usr/bin/sed -e /^\#/d | /usr/bin/sed -e s/XCOMM/\#/ > xmkmf

leads to desired behavior. When cpp 4.8.x reads from stdin, it adds this on top:
# 1 "<stdin>"
# 1 "<command-line>"

# 1 "/usr/include/stdc-predef.h" 1 3 4

# 17 "/usr/include/stdc-predef.h" 3 4
[lots of newlines]
# 1 "<command-line>" 2
# 1 "<stdin>"

Changing it to read from file changes it:
# 1 "./xmkmf.cpp"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "<command-line>" 2
# 1 "./xmkmf.cpp"

Submitted patch to xorg-devel for review:
http://patchwork.freedesktop.org/patch/15784/

Please test to ensure this works for you too.

Fix pushed to git master:
http://cgit.freedesktop.org/xorg/app/xinit/commit/?id=463b85fcf51d8ff5886ebe1f3481e5cb4d603436

Fix published in xinit 1.3.4:
http://lists.x.org/archives/xorg-announce/2014-September/002477.html

FWIW, I just sort of ran into an odd offshoot of this:

https://bugs.freedesktop.org/show_bug.cgi?id=107368

it seems that no-one on this bug or the review threads etc. talked about *why* this change 'fixed' the bug. From some research in #107368 , it seems to me that what's going on is, when passed input via stdin and without any -x parameter, cpp will assume it's C. When passed input as a file with a .cpp extension, cpp assumes it's C++.

For some reason, when it's treating these files as C or assembler, cpp (perhaps only cpp in gcc 4.8+, which is why this suddenly appeared?) adds a bunch of blank lines at the top. When it's treating them as C++, it doesn't.

You can play around with this for yourself by deleting 'startx', running 'make -n' to get the full cpp command that 'make' would run, then renaming the files and modifying the command. For instance, if I leave the input file as 'startx.cpp' but add '-xc' or '-xassembler' to the cpp command (which overrides the file extension-based language detection and just *tells* cpp to treat the file as C or assembler), I get the blank lines. And if I rename the input file to 'startx.foo' but add '-xc++' to the cpp command, I get the file without the blank lines.

So it seems like the 'fix' here was really a sort of slightly odd workaround, and it'd be interesting to figure out why cpp in 4.8 adds these blank lines when treating the code as C whereas cpp in 4.7 perhaps didn't.

I ran across this because the fact that the '.cpp' extension makes cpp treat these files as C++ effectively makes the build depend on gcc-c++, even though there's no C++ code in it at all...