FAILED: patch "[PATCH] gcc-plugins: Undefine LATENT_ENTROPY_PLUGIN when plugin" failed to apply to 4.14-stable tree

The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 012e8d2034f1bda8863435cd589636e618d6a659 Mon Sep 17 00:00:00 2001
From: Andrew Donnellan <[email protected]>
Date: Tue, 16 Aug 2022 15:17:20 +1000
Subject: [PATCH] gcc-plugins: Undefine LATENT_ENTROPY_PLUGIN when plugin
disabled for a file

Commit 36d4b36b6959 ("lib/nodemask: inline next_node_in() and node_random()") refactored some code by moving node_random() from lib/nodemask.c to include/linux/nodemask.h, thus requiring nodemask.h to include random.h, which conditionally defines add_latent_entropy() depending on whether the macro LATENT_ENTROPY_PLUGIN is defined.

This broke the build on powerpc, where nodemask.h is indirectly included in arch/powerpc/kernel/prom_init.c, part of the early boot machinery that is excluded from the latent entropy plugin using DISABLE_LATENT_ENTROPY_PLUGIN. It turns out that while we add a gcc flag to disable the actual plugin, we don't undefine LATENT_ENTROPY_PLUGIN.

This leads to the following:

CC arch/powerpc/kernel/prom_init.o
In file included from ./include/linux/nodemask.h:97,

                   from ./include/linux/mmzone.h:17,
                   from ./include/linux/gfp.h:7,
                   from ./include/linux/xarray.h:15,
                   from ./include/linux/radix-tree.h:21,
                   from ./include/linux/idr.h:15,
                   from ./include/linux/kernfs.h:12,
                   from ./include/linux/sysfs.h:16,
                   from ./include/linux/kobject.h:20,
                   from ./include/linux/pci.h:35,
                   from arch/powerpc/kernel/prom_init.c:24:
  ./include/linux/random.h: In function 'add_latent_entropy':
  ./include/linux/random.h:25:46: error: 'latent_entropy' undeclared (first use in this function); did you mean 'add_latent_entropy'?
     25 |         add_device_randomness((const void *)&latent_entropy, sizeof(latent_entropy));
        |                                              ^~~~~~~~~~~~~~
        |                                              add_latent_entropy

./include/linux/random.h:25:46: note: each undeclared identifier is reported only once for each function it appears in make[2]: *** [scripts/Makefile.build:249: arch/powerpc/kernel/prom_init.o] Fehler 1
make[1]: *** [scripts/Makefile.build:465: arch/powerpc/kernel] Fehler 2
make: *** [Makefile:1855: arch/powerpc] Error 2

Change the DISABLE_LATENT_ENTROPY_PLUGIN flags to undefine LATENT_ENTROPY_PLUGIN for files where the plugin is disabled.

index 692d64a70542..e4deaf5fa571 100644
@@ -4,7 +4,7 @@ gcc-plugin-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)	+= latent_entropy_plugin.so
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)		\
 		+= -DLATENT_ENTROPY_PLUGIN
 ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
-    DISABLE_LATENT_ENTROPY_PLUGIN += -fplugin-arg-latent_entropy_plugin-disable
+    DISABLE_LATENT_ENTROPY_PLUGIN += -fplugin-arg-latent_entropy_plugin-disable -ULATENT_ENTROPY_PLUGIN
 endif
 export DISABLE_LATENT_ENTROPY_PLUGIN