[PATCH] fix multiple definition linking error due to missing extern

[PATCH] fix multiple definition linking error due to missing extern

[Dirk Müller]

GCC 10+ defaults to -fno-common, which enforces proper declaration of
external references using "extern". without this change a link would
fail with:

  lib/raid6/test/algos.c:28: multiple definition of `raid6_call';
  lib/raid6/test/test.c:22: first defined here

Signed-off-by: Dirk Müller <dmueller@suse.de>
---
 lib/raid6/test/test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/raid6/test/test.c b/lib/raid6/test/test.c
index a3cf071941ab..ab0459150a61 100644
--- a/lib/raid6/test/test.c
+++ b/lib/raid6/test/test.c
@@ -19,7 +19,7 @@
 #define NDISKS		16	/* Including P and Q */
 
 const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
-struct raid6_calls raid6_call;
+extern struct raid6_calls raid6_call;
 
 char *dataptrs[NDISKS];
 char data[NDISKS][PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
-- 
2.35.1

Re: [PATCH] fix multiple definition linking error due to missing extern

[Paul Menzel]

Dear Dirk,


Am 06.02.22 um 21:51 schrieb Dirk Müller:

It’d be great of you added a prefix in the commit message summary. Maybe:

> lib/raid6/test: fix multiple definition linking error due to missing extern

> GCC 10+ defaults to -fno-common, which enforces proper declaration of
> external references using "extern". without this change a link would

Nit: Without

> fail with:
> 
>    lib/raid6/test/algos.c:28: multiple definition of `raid6_call';
>    lib/raid6/test/test.c:22: first defined here
> 
> Signed-off-by: Dirk Müller <dmueller@suse.de>

Thank you for properly analyzing and fixing it in a better way than my 
(non-working) attempt [1].

Should it be tagged for the stable series, that means CC’ed to 
<stable@vger.kernel.org>?

> ---
>   lib/raid6/test/test.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/raid6/test/test.c b/lib/raid6/test/test.c
> index a3cf071941ab..ab0459150a61 100644
> --- a/lib/raid6/test/test.c
> +++ b/lib/raid6/test/test.c
> @@ -19,7 +19,7 @@
>   #define NDISKS		16	/* Including P and Q */
>   
>   const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
> -struct raid6_calls raid6_call;
> +extern struct raid6_calls raid6_call;
>   
>   char *dataptrs[NDISKS];
>   char data[NDISKS][PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));

Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>


Kind regards,

Paul


[1]: 
https://lore.kernel.org/linux-raid/20220126114144.370517-3-pmenzel@molgen.mpg.de/T/#u

Re: [PATCH] fix multiple definition linking error due to missing extern

[Song Liu]

On Sun, Feb 6, 2022 at 12:59 PM Dirk Müller <dmueller@suse.de> wrote:
>
> GCC 10+ defaults to -fno-common, which enforces proper declaration of
> external references using "extern". without this change a link would
> fail with:
>
>   lib/raid6/test/algos.c:28: multiple definition of `raid6_call';
>   lib/raid6/test/test.c:22: first defined here
>
> Signed-off-by: Dirk Müller <dmueller@suse.de>
> ---
>  lib/raid6/test/test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/raid6/test/test.c b/lib/raid6/test/test.c
> index a3cf071941ab..ab0459150a61 100644
> --- a/lib/raid6/test/test.c
> +++ b/lib/raid6/test/test.c
> @@ -19,7 +19,7 @@
>  #define NDISKS         16      /* Including P and Q */
>
>  const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
> -struct raid6_calls raid6_call;
> +extern struct raid6_calls raid6_call;

Can we just remove this line?

Thanks,
Song

Re: [PATCH] fix multiple definition linking error due to missing extern

[Dirk Müller]

On Dienstag, 8. Februar 2022 06:45:45 CET Song Liu wrote:

Hi Song,

> > -struct raid6_calls raid6_call;
> > +extern struct raid6_calls raid6_call;
> 
> Can we just remove this line?

oh yes indeed, it is already declared in the header file. that is much simpler. 
I've sent a PATCH v2 just now. 

Thank you,
Dirk

[PATCH] fix multiple definition linking error due to missing extern

[Dirk Müller]

GCC 10+ defaults to -fno-common, which enforces proper declaration of
external references using "extern". without this change a link would
fail with:

  ld: raid6.a(algos.o):lib/raid6/test/algos.c:28: multiple definition of `raid6_call';
                       lib/raid6/test/test.c:22: first defined here

Signed-off-by: Dirk Müller <dmueller@suse.de>
---
 lib/raid6/test/test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/raid6/test/test.c b/lib/raid6/test/test.c
index a3cf071941ab..ab0459150a61 100644
--- a/lib/raid6/test/test.c
+++ b/lib/raid6/test/test.c
@@ -19,7 +19,7 @@
 #define NDISKS		16	/* Including P and Q */
 
 const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
-struct raid6_calls raid6_call;
+extern struct raid6_calls raid6_call;
 
 char *dataptrs[NDISKS];
 char data[NDISKS][PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
-- 
2.34.1