This patch fix "multiple definition of `xprintf'" (or xgt_handle)
build error with GCC 10.1.0.

These are the error reported:
    gcc xs_tdb_dump.o utils.o tdb.o talloc.o      -o xs_tdb_dump
    /usr/bin/ld: utils.o:./utils.h:27: multiple definition of `xprintf'; xs_tdb_dump.o:./utils.h:27: first defined here
    [...]
    gcc xenstored_core.o xenstored_watch.o xenstored_domain.o xenstored_transaction.o xenstored_control.o xs_lib.o talloc.o utils.o tdb.o hashtable.o xenstored_posix.o      -lsystemd   -Wl,-rpath-link=... ../libxc/libxenctrl.so -lrt  -o xenstored
    /usr/bin/ld: xenstored_watch.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
    /usr/bin/ld: xenstored_domain.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
    /usr/bin/ld: xenstored_transaction.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
    /usr/bin/ld: xenstored_control.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
    /usr/bin/ld: xenstored_posix.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here

A difference that I noticed with earlier version of the build chain is
that before, I had:
    $ nm xs_tdb_dump.o | grep xprintf
    0000000000000008 C xprintf
And now, it's:
    0000000000000000 B xprintf
With the patch apply, the symbol isn't in xs_tdb_dump.o anymore.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 tools/xenstore/utils.h          | 2 +-
 tools/xenstore/xenstored_core.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/xenstore/utils.h b/tools/xenstore/utils.h
index 522c3594a2ba..6a1b5de9bdc1 100644
--- a/tools/xenstore/utils.h
+++ b/tools/xenstore/utils.h
@@ -24,7 +24,7 @@ static inline bool strends(const char *a, const char *b)
 void barf(const char *fmt, ...) __attribute__((noreturn));
 void barf_perror(const char *fmt, ...) __attribute__((noreturn));
 
-void (*xprintf)(const char *fmt, ...);
+extern void (*xprintf)(const char *fmt, ...);
 
 #define eprintf(_fmt, _args...) xprintf("[ERR] %s" _fmt, __FUNCTION__, ##_args)
 
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index 56a279cfbb47..c4c32bc88f0c 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -204,7 +204,7 @@ void finish_daemonize(void);
 /* Open a pipe for signal handling */
 void init_pipe(int reopen_log_pipe[2]);
 
-xengnttab_handle **xgt_handle;
+extern xengnttab_handle **xgt_handle;
 
 int remember_string(struct hashtable *hash, const char *str);
 
-- 
Anthony PERARD

On 20/05/2020 17:39, Anthony PERARD wrote:
> This patch fix "multiple definition of `xprintf'" (or xgt_handle)
> build error with GCC 10.1.0.
>
> These are the error reported:
>     gcc xs_tdb_dump.o utils.o tdb.o talloc.o      -o xs_tdb_dump
>     /usr/bin/ld: utils.o:./utils.h:27: multiple definition of `xprintf'; xs_tdb_dump.o:./utils.h:27: first defined here
>     [...]
>     gcc xenstored_core.o xenstored_watch.o xenstored_domain.o xenstored_transaction.o xenstored_control.o xs_lib.o talloc.o utils.o tdb.o hashtable.o xenstored_posix.o      -lsystemd   -Wl,-rpath-link=... ../libxc/libxenctrl.so -lrt  -o xenstored
>     /usr/bin/ld: xenstored_watch.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
>     /usr/bin/ld: xenstored_domain.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
>     /usr/bin/ld: xenstored_transaction.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
>     /usr/bin/ld: xenstored_control.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
>     /usr/bin/ld: xenstored_posix.o:./xenstored_core.h:207: multiple definition of `xgt_handle'; xenstored_core.o:./xenstored_core.h:207: first defined here
>
> A difference that I noticed with earlier version of the build chain is
> that before, I had:
>     $ nm xs_tdb_dump.o | grep xprintf
>     0000000000000008 C xprintf
> And now, it's:
>     0000000000000000 B xprintf
> With the patch apply, the symbol isn't in xs_tdb_dump.o anymore.
>
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

Ah - this will be a side effect of defaulting to -fno-common now.

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

Anthony PERARD writes ("[XEN PATCH] tools/xenstore: mark variable in header as extern"):
> This patch fix "multiple definition of `xprintf'" (or xgt_handle)
> build error with GCC 10.1.0.

Reviewed-by: Ian Jackson <ian.jackson@eu.citrix.com>