[Buildroot] [PATCH/RFC 1/1] package/mesa3d: disable libunwind for Gallium drivers on arm

[Bernd Kuhls]

Building a Gallium driver on ARM is broken if optional libunwind
support is enabled. The build fails here:
https://cgit.freedesktop.org/mesa/mesa/tree/src/gallium/auxiliary/util/u_debug_stack.c?h=17.1#n114

util/u_debug_stack.c:114:4: error: 'unw_base' undeclared (first use in this function)
    unw_getcontext(&context);

unw_base is declared in the libunwind package in
include/libunwind-arm.h:
https://github.com/libunwind/libunwind/blob/7c079200d024d5868073246c4ec8f80446b0a4c0/include/libunwind-arm.h#L262

which contains a comment:

/* There is no getcontext() on ARM.  Use a stub version which only
   saves GP registers.  FIXME: Not ideal, may not be sufficient for
   all libunwind use cases.  Stores pc+8, which is only approximately
   correct, really.  */

To fix the build error we just disable libunwind support on ARM when a
Gallium driver is enabled until upstream comes up with a working
solution. Tested using this defconfig with test_pkg

BR2_PACKAGE_MESA3D=y
BR2_PACKAGE_MESA3D_GALLIUM_DRIVER_SWRAST=y
BR2_PACKAGE_MESA3D_OPENGL_EGL=y
BR2_PACKAGE_MESA3D_OPENGL_ES=y
BR2_PACKAGE_LIBUNWIND=y

without this patch:

                armv5-ctng-linux-gnueabi [ 1/49]: FAILED
              armv7-ctng-linux-gnueabihf [ 2/49]: FAILED
                  br-arm-cortex-a9-glibc [ 6/49]: FAILED

and with this patch:

                armv5-ctng-linux-gnueabi [ 1/49]: OK
              armv7-ctng-linux-gnueabihf [ 2/49]: OK
                  br-arm-cortex-a9-glibc [ 6/49]: OK

Fixes
http://autobuild.buildroot.net/results/3ef/3efe156b6494e4392b6c31de447ee2c72acc1a53/

Signed-off-by: Bernd Kuhls <bernd.kuhls at t-online.de>
---
I have no idea whether the problem can be fixed by patching the code,
disabling libunwind in the gallium at arm case at least fixes the build
error.

 package/mesa3d/mesa3d.mk | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/package/mesa3d/mesa3d.mk b/package/mesa3d/mesa3d.mk
index 04a7d13b9..bc01a37d6 100644
--- a/package/mesa3d/mesa3d.mk
+++ b/package/mesa3d/mesa3d.mk
@@ -193,11 +193,15 @@ MESA3D_CONF_OPTS += --disable-xvmc
 endif
 
 ifeq ($(BR2_PACKAGE_LIBUNWIND),y)
+ifneq ($(BR2_ARM_CPU_HAS_ARM)$(BR2_PACKAGE_MESA3D_GALLIUM_DRIVER),yy)
 MESA3D_CONF_OPTS += --enable-libunwind
 MESA3D_DEPENDENCIES += libunwind
 else
 MESA3D_CONF_OPTS += --disable-libunwind
 endif
+else
+MESA3D_CONF_OPTS += --disable-libunwind
+endif
 
 ifeq ($(BR2_PACKAGE_LIBVDPAU),y)
 MESA3D_DEPENDENCIES += libvdpau
-- 
2.11.0