i965: Build the driver into a shared mesa_dri_drivers.so .

Previously, we've split things such that mesa core is in libdricore,
exposing the whole Mesa core interface in the global namespace, and the
i965_dri.so code all links against that.  Along with polluting application
namespace terribly, it requires extra PLT indirections and prevents LTO.

Instead, we can build all of the driver contents into the same .so with
just a few symbols exposed to be referenced from the actual driver .so
file, allowing LTO and reducing our exposed symbol count massively.

FPS improvement on GLB2.7 with INTEL_NO_HW=1: 2.61061% +/- 1.16957% (n=50)
(without LTO, just the PLT reductions from this commit)

Note that the X Server requires commit
7ecfab47eb221dbb996ea6c033348b8eceaeb893 to successfully load this driver!

v2: Set a global driverAPI variable so loaders don't have to update to
    createNewScreen2() (though they may want to for thread safety).
v3: Drop AM_CPPFLAGS addition (Emil pointed out I'd missed some cflags
    that would be necessary, though only if we actually relied on them).
v4: Fix install with DESTDIR set.

Reviewed-by: Matt Turner <mattst88@gmail.com> (v1)
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com> (v2)

1 files changed, 18 insertions, 1 deletions

diff --git a/src/mesa/drivers/dri/common/dri_util.c b/src/mesa/drivers/dri/common/dri_util.c
index 2a85703..c28b0fc 100644
--- a/src/mesa/drivers/dri/common/dri_util.c
+++ b/src/mesa/drivers/dri/common/dri_util.c
@@ -82,6 +82,23 @@ setupLoaderExtensions(__DRIscreen *psp,
 }
 
 /**
+ * This pointer determines which driver API we'll use in the case of the
+ * loader not passing us an explicit driver extensions list (that would,
+ * itself, contain a pointer to a driver API.)
+ *
+ * A driver's driDriverGetExtensions_drivername() can update this pointer to
+ * what it's returning, and a loader that is ignorant of createNewScreen2()
+ * will get the correct driver screen created, as long as no other
+ * driDriverGetExtensions() happened in between the first one and the
+ * createNewScreen().
+ *
+ * This allows the X Server to not require the significant dri_interface.h
+ * updates for doing createNewScreen2(), which would discourage backporting of
+ * the X Server patches to support the new loader interface.
+ */
+const struct __DriverAPIRec *globalDriverAPI = &driDriverAPI;
+
+/**
  * This is the first entrypoint in the driver called by the DRI driver loader
  * after dlopen()ing it.
  *
@@ -102,7 +119,7 @@ dri2CreateNewScreen2(int scrn, int fd,
 	return NULL;
 
     /* By default, use the global driDriverAPI symbol (non-megadrivers). */
-    psp->driver = &driDriverAPI;
+    psp->driver = globalDriverAPI;
 
     /* If the driver exposes its vtable through its extensions list
      * (megadrivers), use that instead.