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Masahiro Yamada a41c9b5703 kbuild: let fixdep directly write to .*.cmd files 
[ Upstream commit 392885ee82 ]

Currently, fixdep writes dependencies to .*.tmp, which is renamed to
.*.cmd after everything succeeds. This is a very safe way to avoid
corrupted .*.cmd files. The if_changed_dep has carried this safety
mechanism since it was added in 2002.

If fixdep fails for some reasons or a user terminates the build while
fixdep is running, the incomplete output from the fixdep could be
troublesome.

This is my insight about some bad scenarios:

[1] If the compiler succeeds to generate *.o file, but fixdep fails
    to write necessary dependencies to .*.cmd file, Make will miss
    to rebuild the object when headers or CONFIG options are changed.
    In this case, fixdep should not generate .*.cmd file at all so
    that 'arg-check' will surely trigger the rebuild of the object.

[2] A partially constructed .*.cmd file may not be a syntactically
    correct makefile. The next time Make runs, it would include it,
    then fail to parse it. Once this happens, 'make clean' is be the
    only way to fix it.

In fact, [1] is no longer a problem since commit 9c2af1c737 ("kbuild:
add .DELETE_ON_ERROR special target"). Make deletes a target file on
any failure in its recipe. Because fixdep is a part of the recipe of
*.o target, if it fails, the *.o is deleted anyway. However, I am a
bit worried about the slight possibility of [2].

So, here is a solution. Let fixdep directly write to a .*.cmd file,
but allow makefiles to include it only when its corresponding target
exists.

This effectively reverts commit 2982c95357 ("kbuild: remove redundant
$(wildcard ...) for cmd_files calculation"), and commit 00d78ab2ba
("kbuild: remove dead code in cmd_files calculation in top Makefile")
because now we must check the presence of targets.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2019-01-26 09:20:43 +01:00
arch arm64: Use a raw spinlock in __install_bp_hardening_cb() 2019-01-26 09:20:42 +01:00
block block: use rcu_work instead of call_rcu to avoid sleep in softirq 2019-01-22 21:09:57 +01:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: ecc - regularize scalar for scalar multiplication 2019-01-26 09:20:41 +01:00
Documentation x86/speculation/l1tf: Drop the swap storage limit restriction when l1tf=off 2019-01-09 17:45:54 +01:00
drivers efi/libstub: Disable some warnings for x86{,_64} 2019-01-26 09:20:43 +01:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs jffs2: Fix use of uninitialized delayed_work, lockdep breakage 2019-01-26 09:20:43 +01:00
include bpf: Allow narrow loads with offset > 0 2019-01-26 09:20:40 +01:00
init kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace & GCC <= 4.7 2019-01-22 21:09:54 +01:00
ipc ipc: IPCMNI limit check for semmni 2018-10-31 08:54:14 -07:00
kernel bpf: Allow narrow loads with offset > 0 2019-01-26 09:20:40 +01:00
lib fix int_sqrt64() for very large numbers 2019-01-22 21:09:55 +01:00
LICENSES This is a fairly typical cycle for documentation. There's some welcome 2018-10-24 18:01:11 +01:00
mm mm: page_mapped: don't assume compound page is huge or THP 2019-01-16 22:03:26 +01:00
net netfilter: ipset: Allow matching on destination MAC address for mac and ipmac sets 2019-01-26 09:20:39 +01:00
samples samples: bpf: fix: error handling regarding kprobe_events 2019-01-26 09:20:42 +01:00
scripts kbuild: let fixdep directly write to .*.cmd files 2019-01-26 09:20:43 +01:00
security selinux: always allow mounting submounts 2019-01-26 09:20:42 +01:00
sound ASoC: pcm3168a: Don't disable pcm3168a when CONFIG_PM defined 2019-01-26 09:20:42 +01:00
tools selftests/bpf: enable (uncomment) all tests in test_libbpf.sh 2019-01-26 09:20:40 +01:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: arm/arm64: vgic: Fix off-by-one bug in vgic_get_irq() 2019-01-09 17:46:04 +01:00
.clang-format page cache: Convert find_get_pages_contig to XArray 2018-10-21 10:46:34 -04:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap mailmap: Update email for Punit Agrawal 2018-11-05 10:02:11 +00:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: update entry for MMP platform 2018-12-03 12:39:57 -08:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-12-21 14:21:17 -08:00
Makefile kbuild: let fixdep directly write to .*.cmd files 2019-01-26 09:20:43 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.