linux-kernel - Re: [PATCH v2 1/2] kbuild: introduce ccflags-remove-y and asflags-remove-y

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 7 Jul 2020 12:58:01 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild <linux-kbuild@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "David S. Miller" <davem@...emloft.net>,
        Haren Myneni <haren@...ibm.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ingo Molnar <mingo@...hat.com>, Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Miroslav Benes <mbenes@...e.cz>,
        Paul Mackerras <paulus@...ba.org>,
        Petr Mladek <pmladek@...e.com>, Rich Felker <dalias@...c.org>,
        Russell King <linux@...linux.org.uk>,
        Tal Gilboa <talgi@...lanox.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        KUnit Development <kunit-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-crypto@...r.kernel.org,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, linux-sh@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, live-patching@...r.kernel.org
Subject: Re: [PATCH v2 1/2] kbuild: introduce ccflags-remove-y and asflags-remove-y

On Tue, Jul 7, 2020 at 2:22 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> CFLAGS_REMOVE_<file>.o filters out flags when compiling a particular
> object, but there is no convenient way to do that for every object in
> a directory.
>
> Add ccflags-remove-y and asflags-remove-y to make it easily.
>
> Use ccflags-remove-y to clean up some Makefiles.
>
> The add/remove order works as follows:
>
>  [1] KBUILD_CFLAGS specifies compiler flags used globally
>
>  [2] ccflags-y adds compiler flags for all objects in the
>      current Makefile
>
>  [3] ccflags-remove-y removes compiler flags for all objects in the
>      current Makefile (New feature)
>
>  [4] CFLAGS_<file> adds compiler flags per file.
>
>  [5] CFLAGS_REMOVE_<file> removes compiler flags per file.
>
> Having [3] before [4] allows us to remove flags from most (but not all)
> objects in the current Makefile.
>
> For example, kernel/trace/Makefile removes $(CC_FLAGS_FTRACE)
> from all objects in the directory, then adds it back to
> trace_selftest_dynamic.o and CFLAGS_trace_kprobe_selftest.o
>
> Please note ccflags-remove-y has no effect to the sub-directories.
> In contrast, the previous notation got rid of compiler flags also from
> all the sub-directories.
>
>   arch/arm/boot/compressed/
>   arch/powerpc/xmon/
>   arch/sh/
>   kernel/trace/
>
> ... have no sub-directories.
>
>   lib/
>
> ... has several sub-directories.
>
> To keep the behavior, I added ccflags-remove-y to all Makefiles
> in subdirectories of lib/, except:
>
>   lib/vdso/Makefile        - Kbuild does not descend into this Makefile
>   lib/raid/test/Makefile   - This is not used for the kernel build
>
> I think commit 2464a609ded0 ("ftrace: do not trace library functions")
> excluded too much. In later commit, I will try to remove ccflags-remove-y
> from sub-directory Makefiles.
>
> Suggested-by: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)

Acked-by: Brendan Higgins <brendanhiggins@...gle.com> (KUnit)