Hi,
I am building GDB from git, because I want to hack on GDB. I have a few
build-related things in my profile, including GCC. I enter an
environment for GDB like this:
guix environment gdb --ad-hoc flex autoconf-2.64
Cool. Very good. I build:
mkdir +2.0
cd +2.0
../configure --prefix=/opt/gdb
make
However, eventually:
/bin/sh ./libtool --tag=CC --mode=compile ccache gcc -DHAVE_CONFIG_H -I.
-I../../bfd -I. -I../../bfd -I../../bfd/../include -DHAVE_x86_64_elf64_vec
-DHAVE_i386_elf32_vec -DHAVE_iamcu_elf32_vec -DHAVE_x86_64_elf32_vec
-DHAVE_i386_aout_linux_vec -DHAVE_i386_pei_vec -DHAVE_x86_64_pei_vec
-DHAVE_l1om_elf64_vec -DHAVE_k1om_elf64_vec -DHAVE_elf64_le_vec
-DHAVE_elf64_be_vec -DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_plugin_vec
-DBINDIR='"/opt/guile-2.0/bin"' -W -Wall -Wstrict-prototypes
-Wmissing-prototypes -Wshadow -Werror -I../../bfd/../zlib -g -O2 -MT peigen.lo
-MD -MP -MF .deps/peigen.Tpo -c -o peigen.lo peigen.c
libtool: compile: ccache gcc -DHAVE_CONFIG_H -I. -I../../bfd -I. -I../../bfd
-I../../bfd/../include -DHAVE_x86_64_elf64_vec -DHAVE_i386_elf32_vec
-DHAVE_iamcu_elf32_vec -DHAVE_x86_64_elf32_vec -DHAVE_i386_aout_linux_vec
-DHAVE_i386_pei_vec -DHAVE_x86_64_pei_vec -DHAVE_l1om_elf64_vec
-DHAVE_k1om_elf64_vec -DHAVE_elf64_le_vec -DHAVE_elf64_be_vec
-DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_plugin_vec
-DBINDIR=\"/opt/guile-2.0/bin\" -W -Wall -Wstrict-prototypes
-Wmissing-prototypes -Wshadow -Werror -I../../bfd/../zlib -g -O2 -MT peigen.lo
-MD -MP -MF .deps/peigen.Tpo -c peigen.c -o peigen.o
In file included from peigen.c:66:0:
/home/wingo/.guix-profile/include/wchar.h: In function 'wctob':
/home/wingo/.guix-profile/include/wchar.h:397:47: error: comparison of
unsigned expression >= 0 is always true [-Werror=type-limits]
{ return (__builtin_constant_p (__wc) && __wc >= L'\0' && __wc <= L'\x7f'
^
This is an error, and the error is in wchar.h, not in the invocation or
use of wchar.h. Let's see where this file comes from:
ls -l /home/wingo/.guix-profile/include/wchar.h
lrwxrwxrwx 21 root guixbuild 79 Jan 1 1970
/home/wingo/.guix-profile/include/wchar.h ->
/gnu/store/q7k2dc3ylpjnjlhb59f01bxxab8fjxr6-gcc-toolchain-5.2.0/include/wchar.h
So! gcc-toolchain-5.2. Why is there an error? Well, of course,
although harmless, the "error" exists in the source, though perhaps GCC
itself doesn't build with -Werror=type-limits, so they didn't see this
error in the release. The error comes from the combination of the
-Werror and warning flags that GDB is building with and the files from
gcc-toolchain.
Backing up a bit, it's not something that I actually care about right
now. I'm working on GDB, the error is innocuous, and I can't easily fix
GCC right now, nor do I care. I'm also surprised this is happening --
wouldn't it be caught by some other distro user? Well yes, except that
normally this header is in /usr/include, and by default, all warnings
are disabled for system headers.
And there's the rub! Why am I getting a warning for code in
~/.guix-profile/include ?
The answer is interesting! I quote the GCC manual, section "Environment
Variables":
Some additional environment variables affect the behavior of the
preprocessor.
'CPATH'
'C_INCLUDE_PATH'
'CPLUS_INCLUDE_PATH'
'OBJC_INCLUDE_PATH'
Each variable's value is a list of directories separated by a
special character, much like 'PATH', in which to look for header
files. The special character, 'PATH_SEPARATOR', is
target-dependent and determined at GCC build time. For Microsoft
Windows-based targets it is a semicolon, and for almost all other
targets it is a colon.
'CPATH' specifies a list of directories to be searched as if
specified with '-I', but after any paths given with '-I' options on
the command line. This environment variable is used regardless of
which language is being preprocessed.
The remaining environment variables apply only when preprocessing
the particular language indicated. Each specifies a list of
directories to be searched as if specified with '-isystem', but
after any paths given with '-isystem' options on the command line.
In all these variables, an empty element instructs the compiler to
search its current working directory. Empty elements can appear at
the beginning or end of a path. For instance, if the value of
'CPATH' is ':/special/include', that has the same effect as
'-I. -I/special/include'.
So! CPATH is like -I but C_INCLUDE_PATH et al are like -isystem.
Here's the docs for -isystem ("Preprocessor Options"):
'-isystem DIR'
Search DIR for header files, after all directories specified by
'-I' but before the standard system directories. Mark it as a
system director
