kconfig.h was excluded from consideration by fixdep by
6a5be57f0f00 (fixdep: fix extraneous dependencies) to avoid some false
positive hits

(1) include/config/.h
(2) include/config/h.h
(3) include/config/foo.h

(1) occurred because kconfig.h contains the string CONFIG_ in a
comment. However, since dee81e988674 (fixdep: faster CONFIG_ search), we
have a check that the part after CONFIG_ is non-empty, so this does not
happen anymore (and CONFIG_ appears by itself elsewhere, so that check
is worthwhile).

(2) comes from the include guard, __LINUX_KCONFIG_H. But with the
previous patch, we no longer match that either.

That leaves (3), which amounts to one [1] false dependency (aka stat() call
done by make), which I think we can live with:

We've already had one case [2] where the lack of include/linux/kconfig.h in
the .o.cmd file caused a missing rebuild, and while I originally thought
we should just put kconfig.h in the dependency list without parsing it
for the CONFIG_ pattern, we actually do have some real CONFIG_ symbols
mentioned in it, and one can imagine some translation unit that just
does '#ifdef __BIG_ENDIAN' but doesn't through some other header
actually depend on CONFIG_CPU_BIG_ENDIAN - so changing the target
endianness could end up rebuilding the world, minus that small
TU. Quoting Linus,

  ... when missing dependencies cause a missed re-compile, the resulting
  bugs can be _really_ subtle.

[1] well, two, we now also have CONFIG_BOOGER/booger.h - we could change
that to FOO if we care

[2] https://lkml.org/lkml/2018/2/22/838

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

The string CONFIG_ quite often appears after other alphanumerics,
meaning that that instance cannot be referencing a Kconfig
symbol. Omitting these means make has fewer files to stat() when
deciding what needs to be rebuilt - for a defconfig build, this seems to
remove about 2% of the (wildcard ...) lines from the .o.cmd files.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

uml-config.h hasn't existed in this decade (87e299e5c750 - x86, um: get
rid of uml-config.h). The few remaining UML_CONFIG instances are defined
directly in terms of their real CONFIG symbol in common-offsets.h, so
unlike when the symbols got defined via a sed script, anything that uses
UML_CONFIG_FOO now should also automatically pick up a dependency on
CONFIG_FOO via the normal fixdep mechanism (since common-offsets.h
should at least recursively be a dependency). Hence I believe we should
actually be able to ignore the HELLO_CONFIG_BOOM cases.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Richard Weinberger <richard@nod.at>
Cc: user-mode-linux-devel@lists.sourceforge.net
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

str_ends_with() tests if the given token ends with a particular string.
Currently, it is used to check file paths without $(srctree).

Actually, we have one more place where this helper is useful.  Use it
to check if CONFIG option ends with _MODULE.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

parse_dep_file() has too much indentation, and puts the code far to
the right.  This commit refactors the code and reduces the one level
of indentation.

strrcmp() computes 'slen' by itself, but the caller already knows the
length of the token, so 'slen' can be passed via function argument.
With this, we can swap the order of strrcmp() and "*p = \0;"

Also, strrcmp() is an ambiguous function name.  Flip the logic and
rename it to str_ends_with().

I added a new helper is_ignored_file() - this returns 1 if the token
represents a file that should be ignored.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

I do not mind global variables where they are useful enough.  In this
case, I do not see a good reason to use global variables since they
are just referenced in shallow places.  It is easy to pass them via
function arguments.

I squashed print_cmdline() into main() since it is just one line code.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Each token in the depfile is copied to the temporary buffer 's' to
terminate the token with zero.  We do not need to do this any more
because the parsed buffer is now writable.  Insert '\0' directly in
the buffer without calling memcpy().

<limits.h> is no longer necessary. (It was needed for PATH_MAX).

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Now, do_config_files() and print_deps() are almost the same.  Only
the difference is the parser function called (parse_config_file vs
parse_dep_file).

We can reduce the code duplication by factoring out the common code
into read_file() - this function allocates a buffer and loads a file
to it.  It returns the pointer to the allocated buffer.  (As before,
it bails out by exit(2) for any error.)  The caller must free the
buffer when done.

Having empty source files is possible; fixdep should simply skip them.
I deleted the "st.st_size == 0" check, so read_file() allocates 1-byte
buffer for an empty file.  strstr() will immediately return NULL, and
this is what we expect.

On the other hand, an empty dep_file should be treated as an error.
In this case, parse_dep_file() will error out with "no targets found"
and it is a correct error message.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Commit dee81e988674 ("fixdep: faster CONFIG_ search") changed how to
read files in which CONFIG options are searched.  It used malloc()
and read() instead of mmap() because it needed to zero-terminate the
buffer in order to use strstr().  print_deps() was left untouched
since there was no reason to change it.

Now, I have two motivations to change it in the same way.

 - do_config_file() and print_deps() do quite similar things; they
   open a file, load it onto memory, and pass it to a parser function.
   If we use malloc() and read() for print_deps() too, we can factor
   out the common code.  (I will do this in the next commit.)

 - parse_dep_file() copies each token to a temporary buffer because
   it needs to zero-terminate it to be passed to printf().  It is not
   possible to modify the buffer directly because it is mmap'ed with
   O_RDONLY.  If we load the file content into a malloc'ed buffer, we
   can insert '\0' after each token, and save memcpy().  (I will do
   this in the commit after next.)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

<arpa/inet.h> was included for ntohl(), but it was removed by
commit dee81e988674 ("fixdep: faster CONFIG_ search").

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>