linux-kernel - Re: remaining flexible-array conversions

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Message-ID: <20200424034704.GA12320@ubuntu-s3-xlarge-x86>
Date:   Thu, 23 Apr 2020 20:47:04 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-rdma@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: remaining flexible-array conversions

Hi Gustavo,

On Wed, Apr 22, 2020 at 01:26:02PM -0500, Gustavo A. R. Silva wrote:
> Hi Linus,
> 
> Just wanted to ask you if you would agree on pulling the remaining
> flexible-array conversions all at once, after they bake for a couple
> of weeks in linux-next[1]
> 
> This is not a disruptive change and there are no code generation
> differences. So, I think it would make better use of everyone's time
> if you pull this treewide patch[2] from my tree (after sending you a
> proper pull-request, of course) sometime in the next couple of weeks.
> 
> Notice that the treewide patch I mention here has been successfully
> built (on top of v5.7-rc1) for multiple architectures (arm, arm64,
> sparc, powerpc, ia64, s390, i386, nios2, c6x, xtensa, openrisc, mips,
> parisc, x86_64, riscv, sh, sparc64) and 82 different configurations
> with the help of the 0-day CI guys[3].
> 
> What do you think?
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=d496496793ff69c4a6b1262a0001eb5cd0a56544
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?h=for-next/kspp&id=d783301058f3d3605f9ad34f0192692ef572d663
> [3] https://github.com/GustavoARSilva/linux-hardening/blob/master/cii/kernel-ci/kspp-fam0-20200420.md
> 
> Thanks
> --
> Gustavo

That patch in -next appears to introduce some warnings with clang when
CONFIG_UAPI_HEADER_TEST is enabled (allyesconfig/allmodconfig exposed it
for us with KernelCI [1]):

./usr/include/rdma/ib_user_verbs.h:436:34: warning: field 'base' with
variable sized type 'struct ib_uverbs_create_cq_resp' not at the end of
a struct or class is a GNU extension
[-Wgnu-variable-sized-type-not-at-end]
        struct ib_uverbs_create_cq_resp base;
                                        ^
./usr/include/rdma/ib_user_verbs.h:647:34: warning: field 'base' with
variable sized type 'struct ib_uverbs_create_qp_resp' not at the end of
a struct or class is a GNU extension
[-Wgnu-variable-sized-type-not-at-end]
        struct ib_uverbs_create_qp_resp base;
                                        ^
./usr/include/rdma/ib_user_verbs.h:743:29: warning: field 'base' with
variable sized type 'struct ib_uverbs_modify_qp' not at the end of a
struct or class is a GNU extension
[-Wgnu-variable-sized-type-not-at-end]
        struct ib_uverbs_modify_qp base;
                                   ^
3 warnings generated.

I presume this is part of the point of the conversion since you mention
a compiler warning when the flexible member is not at the end of a
struct. How should they be fixed? That should probably happen before the
patch gets merged.

[1]: https://kernelci.org/build/id/5ea17b1b77113098348ec6db/logs/

Cheers,
Nathan