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From:   Denis Efremov <efremov@linux.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>,
        linux-kbuild@vger.kernel.org
Cc:     Johannes Berg <johannes@sipsolutions.net>,
        Michal Marek <michal.lkml@markovi.net>,
        linux-kernel@vger.kernel.org
References: <20190924120740.12425-1-yamada.masahiro@socionext.com>
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Subject: Re: [PATCH] modpost: fix static EXPORT_SYMBOL warnings for UML build
Message-ID: <e533db1a-7d68-4119-082c-75b9307f1f2a@linux.com>
Date:   Wed, 25 Sep 2019 21:48:26 +0300
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In-Reply-To: <20190924120740.12425-1-yamada.masahiro@socionext.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On 24.09.2019 15:07, Masahiro Yamada wrote:
> Johannes Berg reports lots of modpost warnings on ARCH=um builds:
> 
> WARNING: "rename" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "lseek" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "ftruncate64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "getuid" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "lseek64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "unlink" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "pwrite64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "close" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "opendir" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "pread64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "syscall" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "readdir" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "readdir64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "futimes" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__lxstat" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "write" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "closedir" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__xstat" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "fsync" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__lxstat64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__fxstat64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "telldir" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "printf" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "readlink" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__sprintf_chk" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "link" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "rmdir" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "fdatasync" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "truncate" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "statfs" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__errno_location" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__xmknod" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "open64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "truncate64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "open" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "read" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "chown" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "chmod" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "utime" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "fchmod" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "seekdir" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "ioctl" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "dup2" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "statfs64" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "utimes" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "mkdir" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "fchown" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__guard" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "symlink" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "access" [vmlinux] is a static EXPORT_SYMBOL
> WARNING: "__stack_smash_handler" [vmlinux] is a static EXPORT_SYMBOL
> 
> When you run "make", the modpost is run twice; before linking vmlinux,
> and before building modules. All the warnings above are from the second
> modpost.
> 
> The offending symbols are defined not in vmlinux, but in the C library.
> The first modpost is run against the relocatable vmlinux.o, and those
> warnings are nicely suppressed because the SH_UNDEF entries from the
> symbol table clear the ->is_static flag.
> 
> The second modpost is run against the executable vmlinux (+ modules),
> where those symbols have been resolved, but the definitions do not
> exist.
> 
> This commit fixes it in a straight forward way. Suppress the static
> EXPORT_SYMBOL warnings from "vmlinux".
> 
> We see the same warnings twice anyway. For example, ARCH=arm64 defconfig
> shows the following warning twice:
> 
> WARNING: "HYPERVISOR_platform_op" [vmlinux] is a static EXPORT_SYMBOL_GPL
> 
> So, it is reasonable to suppress the second one.

Thanks, for fixing it. You can add my if you need
Tested-by: Denis Efremov <efremov@linux.com>

Tested on x86_64 and um arches. I've reverted the commit b08918fb3f2
"lz4: do not export static symbol" and checked for the warning. On um arch I've
tested that this fixes the false-positives.

> 
> Fixes: 15bfc2348d54 ("modpost: check for static EXPORT_SYMBOL* functions")
> Reported-by: Johannes Berg <johannes@sipsolutions.net>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
> 
>  scripts/mod/modpost.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 3961941e8e7a..442d5e2ad688 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -2652,15 +2652,20 @@ int main(int argc, char **argv)
>  		fatal("modpost: Section mismatches detected.\n"
>  		      "Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.\n");
>  	for (n = 0; n < SYMBOL_HASH_SIZE; n++) {
> -		struct symbol *s = symbolhash[n];
> +		struct symbol *s;
> +
> +		for (s = symbolhash[n]; s; s = s->next) {
> +			/*
> +			 * Do not check "vmlinux". This avoids the same warnings
> +			 * shown twice, and false-positives for ARCH=um.
> +			 */
> +			if (is_vmlinux(s->module->name) && !s->module->is_dot_o)
> +				continue;
>  
> -		while (s) {
>  			if (s->is_static)
>  				warn("\"%s\" [%s] is a static %s\n",
>  				     s->name, s->module->name,
>  				     export_str(s->export));
> -
> -			s = s->next;
>  		}
>  	}
>  
>