[Libguestfs] [PATCH nbdkit] Set visibility to default for exported symbols
Daniel P. Berrangé
berrange at redhat.com
Wed Jun 2 20:42:52 UTC 2021
On Wed, Jun 02, 2021 at 09:05:26PM +0100, Richard W.M. Jones wrote:
> In plugins we expect the plugin_init function to be exported as well
> as *_debug_* variables. In the server various nbdkit_* functions
> should be exported.
>
> If you compile nbdkit with -fvisibility=hidden some of these symbols
> are not exported at all even though the linker script says they should
> be. This option can be useful as it allows the compiler to generate
> simpler and hence faster code, and it's required for Clang CFI.
>
> Set the visibility to "default" for all symbols we expect to be
> exported. In theory this should also be required for all the nbdkit_*
> functions exported by the server, but I found that it is not needed by
> either GCC or Clang.
This is kinda wierd, as it feels like we're duplicating information
that is already available in the linker script, but I guess the clue
is in the name of the latter. The visibility option is processed by
the compiler, while the linker script is processed by the linker
and thus too late for the compiler to use.
It is annoying to have to maintain both a .syms script and the source
level annotations. Perhaps there is value in a script that looks for
the NBDKIT_DLL_PUBLIC annotations and uses them to auto-generated a
.syms file for the linker ?
> ---
> include/nbdkit-common.h | 6 +++++-
> include/nbdkit-filter.h | 1 +
> include/nbdkit-plugin.h | 1 +
> tests/Makefile.am | 1 +
> plugins/ocaml/bindings.c | 26 +++++++++++++-------------
> plugins/ocaml/plugin.c | 14 +++++++-------
> tests/dummy-vddk.c | 30 ++++++++++++++++--------------
> 7 files changed, 44 insertions(+), 35 deletions(-)
>
> diff --git a/include/nbdkit-common.h b/include/nbdkit-common.h
> index 51a6264c..f43ebe59 100644
> --- a/include/nbdkit-common.h
> +++ b/include/nbdkit-common.h
> @@ -83,10 +83,14 @@ extern "C" {
> #define NBDKIT_EXTENT_ZERO (1<<1) /* Same as NBD_STATE_ZERO */
>
> #ifndef WIN32
> -#define NBDKIT_EXTERN_DECL(ret, fn, args) extern ret fn args
> +#define NBDKIT_EXTERN_DECL(ret, fn, args) \
> + __attribute__((__visibility__("default"))) \
> + extern ret fn args
> +#define NBDKIT_DLL_PUBLIC __attribute__((__visibility__("default")))
> #else
> #define NBDKIT_EXTERN_DECL(ret, fn, args) \
> extern __declspec(dllexport) ret fn args
> +#define NBDKIT_DLL_PUBLIC __declspec(dllimport)
> #endif
>
> NBDKIT_EXTERN_DECL (void, nbdkit_error,
> diff --git a/include/nbdkit-filter.h b/include/nbdkit-filter.h
> index 633d34e7..8b587d70 100644
> --- a/include/nbdkit-filter.h
> +++ b/include/nbdkit-filter.h
> @@ -263,6 +263,7 @@ struct nbdkit_filter {
>
> #define NBDKIT_REGISTER_FILTER(filter) \
> NBDKIT_CXX_LANG_C \
> + NBDKIT_DLL_PUBLIC \
> struct nbdkit_filter * \
> filter_init (void) \
> { \
> diff --git a/include/nbdkit-plugin.h b/include/nbdkit-plugin.h
> index 611987c7..59ec11b6 100644
> --- a/include/nbdkit-plugin.h
> +++ b/include/nbdkit-plugin.h
> @@ -154,6 +154,7 @@ NBDKIT_EXTERN_DECL (int, nbdkit_is_tls, (void));
>
> #define NBDKIT_REGISTER_PLUGIN(plugin) \
> NBDKIT_CXX_LANG_C \
> + NBDKIT_DLL_PUBLIC \
> struct nbdkit_plugin * \
> plugin_init (void) \
> { \
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index ae801290..acb74fa8 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -1027,6 +1027,7 @@ libvixDiskLib_la_SOURCES = \
> $(NULL)
> libvixDiskLib_la_CPPFLAGS = \
> -I$(top_srcdir)/plugins/vddk \
> + -I$(top_srcdir)/include \
> $(NULL)
> libvixDiskLib_la_CXXFLAGS = $(WARNINGS_CFLAGS)
> # For use of the -rpath option, see:
> diff --git a/plugins/ocaml/bindings.c b/plugins/ocaml/bindings.c
> index 493b147b..a6d57084 100644
> --- a/plugins/ocaml/bindings.c
> +++ b/plugins/ocaml/bindings.c
> @@ -51,7 +51,7 @@
> /* Bindings for miscellaneous nbdkit_* utility functions. */
>
> /* NB: noalloc function. */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_set_error (value nv)
> {
> int err;
> @@ -77,7 +77,7 @@ ocaml_nbdkit_set_error (value nv)
> return Val_unit;
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_parse_size (value strv)
> {
> CAMLparam1 (strv);
> @@ -92,7 +92,7 @@ ocaml_nbdkit_parse_size (value strv)
> CAMLreturn (rv);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_parse_bool (value strv)
> {
> CAMLparam1 (strv);
> @@ -107,7 +107,7 @@ ocaml_nbdkit_parse_bool (value strv)
> CAMLreturn (rv);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_read_password (value strv)
> {
> CAMLparam1 (strv);
> @@ -124,7 +124,7 @@ ocaml_nbdkit_read_password (value strv)
> CAMLreturn (rv);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_realpath (value strv)
> {
> CAMLparam1 (strv);
> @@ -140,7 +140,7 @@ ocaml_nbdkit_realpath (value strv)
> CAMLreturn (rv);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_nanosleep (value secv, value nsecv)
> {
> CAMLparam2 (secv, nsecv);
> @@ -155,7 +155,7 @@ ocaml_nbdkit_nanosleep (value secv, value nsecv)
> CAMLreturn (Val_unit);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_export_name (value unitv)
> {
> CAMLparam1 (unitv);
> @@ -174,7 +174,7 @@ ocaml_nbdkit_export_name (value unitv)
> }
>
> /* NB: noalloc function. */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_shutdown (value unitv)
> {
> CAMLparam1 (unitv);
> @@ -184,7 +184,7 @@ ocaml_nbdkit_shutdown (value unitv)
> }
>
> /* NB: noalloc function. */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_debug (value strv)
> {
> nbdkit_debug ("%s", String_val (strv));
> @@ -192,7 +192,7 @@ ocaml_nbdkit_debug (value strv)
> return Val_unit;
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_version (value unitv)
> {
> CAMLparam1 (unitv);
> @@ -202,7 +202,7 @@ ocaml_nbdkit_version (value unitv)
> CAMLreturn (rv);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_peer_pid (value unitv)
> {
> CAMLparam1 (unitv);
> @@ -213,7 +213,7 @@ ocaml_nbdkit_peer_pid (value unitv)
> CAMLreturn (rv);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_peer_uid (value unitv)
> {
> CAMLparam1 (unitv);
> @@ -224,7 +224,7 @@ ocaml_nbdkit_peer_uid (value unitv)
> CAMLreturn (rv);
> }
>
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_peer_gid (value unitv)
> {
> CAMLparam1 (unitv);
> diff --git a/plugins/ocaml/plugin.c b/plugins/ocaml/plugin.c
> index dc2559b5..00959cb6 100644
> --- a/plugins/ocaml/plugin.c
> +++ b/plugins/ocaml/plugin.c
> @@ -85,7 +85,7 @@ static struct nbdkit_plugin plugin = {
> .unload = unload_wrapper,
> };
>
> -struct nbdkit_plugin *
> +NBDKIT_DLL_PUBLIC struct nbdkit_plugin *
> plugin_init (void)
> {
> if (plugin.name == NULL) {
> @@ -743,7 +743,7 @@ cache_wrapper (void *h, uint32_t count, uint64_t offset, uint32_t flags)
> */
>
> /* NB: noalloc function */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_set_name (value namev)
> {
> plugin.name = strdup (String_val (namev));
> @@ -751,7 +751,7 @@ ocaml_nbdkit_set_name (value namev)
> }
>
> /* NB: noalloc function */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_set_longname (value longnamev)
> {
> plugin.longname = strdup (String_val (longnamev));
> @@ -759,7 +759,7 @@ ocaml_nbdkit_set_longname (value longnamev)
> }
>
> /* NB: noalloc function */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_set_version (value versionv)
> {
> plugin.version = strdup (String_val (versionv));
> @@ -767,7 +767,7 @@ ocaml_nbdkit_set_version (value versionv)
> }
>
> /* NB: noalloc function */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_set_description (value descriptionv)
> {
> plugin.description = strdup (String_val (descriptionv));
> @@ -775,7 +775,7 @@ ocaml_nbdkit_set_description (value descriptionv)
> }
>
> /* NB: noalloc function */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_set_config_help (value helpv)
> {
> plugin.config_help = strdup (String_val (helpv));
> @@ -783,7 +783,7 @@ ocaml_nbdkit_set_config_help (value helpv)
> }
>
> /* NB: noalloc function */
> -value
> +NBDKIT_DLL_PUBLIC value
> ocaml_nbdkit_set_field (value fieldv, value fv)
> {
> const char *field = String_val (fieldv);
> diff --git a/tests/dummy-vddk.c b/tests/dummy-vddk.c
> index c100fc8f..9b5ae0a2 100644
> --- a/tests/dummy-vddk.c
> +++ b/tests/dummy-vddk.c
> @@ -42,6 +42,8 @@
>
> #include <pthread.h>
>
> +#include "nbdkit-plugin.h" /* only for NBDKIT_DLL_PUBLIC */
> +
> #include "vddk-structs.h"
>
> #define STUB(fn,ret,args) extern ret fn args;
> @@ -64,7 +66,7 @@ bg_thread (void *datav)
> return NULL;
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_InitEx (uint32_t major, uint32_t minor,
> VixDiskLibGenericLogFunc *log_function,
> VixDiskLibGenericLogFunc *warn_function,
> @@ -88,32 +90,32 @@ VixDiskLib_InitEx (uint32_t major, uint32_t minor,
> return VIX_OK;
> }
>
> -void
> +NBDKIT_DLL_PUBLIC void
> VixDiskLib_Exit (void)
> {
> /* Do nothing. */
> }
>
> -char *
> +NBDKIT_DLL_PUBLIC char *
> VixDiskLib_GetErrorText (VixError err, const char *unused)
> {
> return strdup ("dummy-vddk: error message");
> }
>
> -void
> +NBDKIT_DLL_PUBLIC void
> VixDiskLib_FreeErrorText (char *text)
> {
> free (text);
> }
>
> -void
> +NBDKIT_DLL_PUBLIC void
> VixDiskLib_FreeConnectParams (VixDiskLibConnectParams *params)
> {
> /* never called since we don't define optional AllocateConnectParams */
> abort ();
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_ConnectEx (const VixDiskLibConnectParams *params,
> char read_only,
> const char *snapshot_ref,
> @@ -129,7 +131,7 @@ VixDiskLib_ConnectEx (const VixDiskLibConnectParams *params,
> return VIX_OK;
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_Open (const VixDiskLibConnection connection,
> const char *path,
> uint32_t flags,
> @@ -142,25 +144,25 @@ VixDiskLib_Open (const VixDiskLibConnection connection,
> return VIX_OK;
> }
>
> -const char *
> +NBDKIT_DLL_PUBLIC const char *
> VixDiskLib_GetTransportMode (VixDiskLibHandle handle)
> {
> return "file";
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_Close (VixDiskLibHandle handle)
> {
> return VIX_OK;
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_Disconnect (VixDiskLibConnection connection)
> {
> return VIX_OK;
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_GetInfo (VixDiskLibHandle handle,
> VixDiskLibInfo **info)
> {
> @@ -169,13 +171,13 @@ VixDiskLib_GetInfo (VixDiskLibHandle handle,
> return VIX_OK;
> }
>
> -void
> +NBDKIT_DLL_PUBLIC void
> VixDiskLib_FreeInfo (VixDiskLibInfo *info)
> {
> free (info);
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_Read (VixDiskLibHandle handle,
> uint64_t start_sector, uint64_t nr_sectors,
> unsigned char *buf)
> @@ -186,7 +188,7 @@ VixDiskLib_Read (VixDiskLibHandle handle,
> return VIX_OK;
> }
>
> -VixError
> +NBDKIT_DLL_PUBLIC VixError
> VixDiskLib_Write (VixDiskLibHandle handle,
> uint64_t start_sector, uint64_t nr_sectors,
> const unsigned char *buf)
> --
> 2.31.1
>
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> Libguestfs at redhat.com
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>
Regards,
Daniel
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