linux-kernel - Re: Difficulties for compilation without extra optimisation

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Date:   Sun, 3 Dec 2017 15:17:32 +0000
From:   Trond Myklebust <trondmy@...marydata.com>
To:     "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "elfring@...rs.sourceforge.net" <elfring@...rs.sourceforge.net>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>
Subject: Re: Difficulties for compilation without extra optimisation

On Sun, 2017-12-03 at 15:15 +0100, SF Markus Elfring wrote:
> Hello,
> 
> I came along some software modules where I suggested source code
> adjustments.
> 
> Example:
> nfs/write: Use common error handling code in
> nfs_lock_and_join_requests()
> 
> https://lkml.org/lkml/2017/11/7/599
> https://patchwork.kernel.org/patch/10047013/
> https://lkml.kernel.org/r/<7f072f78-eef4-6d87-d233-cee71dac5a32@...rs
> .sourceforge.net>;
> 
> I would like to check corresponding build results then without extra
> optimisation applied by the compiler.
> But I got surprised by error messages for a command like the
> following.
> 
> elfring@...ne:~/Projekte/Linux/next-patched> my_cc=/usr/bin/gcc-7 &&
> LANG=C make -j4 CC="${my_cc}" HOSTCC="${my_cc}" EXTRA_CFLAGS='-O0'
> allmodconfig fs/nfs/write.o
> …
> In file included from ./include/linux/compiler.h:58:0,
>                  from ./include/uapi/linux/stddef.h:1,
>                  from ./include/linux/stddef.h:4,
>                  from ./include/uapi/linux/posix_types.h:4,
>                  from ./include/uapi/linux/types.h:13,
>                  from ./include/linux/types.h:5,
>                  from fs/nfs/write.c:9:
> ./arch/x86/include/asm/jump_label.h: In function
> ‘trace_nfs_writeback_page_enter’:
> ./include/linux/compiler-gcc.h:275:38: warning: asm operand 0
> probably doesn’t match constraints
>  #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while
> (0)
> …
> 
> 
> How do you think about to improve this software situation anyhow?

I'm not seeing anything obviously wrong with the NFS use of tracepoints
there, and the warning suggests rather that gcc has an issue with the
inlined assembly code in jump_label.h.

Ccing Peter Zijlstra (who appears to have been the last person to touch
that assembly code) and Steven Rostedt.

-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@...marydata.com