linux-kernel - [PATCH] latent_entropy: avoid build error when plugin cflags are not set

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Date:   Tue, 7 May 2019 16:28:15 +0200
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Emese Revfy <re.emese@...il.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] latent_entropy: avoid build error when plugin cflags are not
 set

Some architectures set up CFLAGS for linux decompressor phase from
scratch and do not include GCC_PLUGINS_CFLAGS. Since "latent_entropy"
variable declaration is generated by the plugin code itself including
linux/random.h in decompressor code then would cause a build
error. E.g. on s390:

In file included from ./include/linux/net.h:22,
                 from ./include/linux/skbuff.h:29,
                 from ./include/linux/if_ether.h:23,
                 from ./arch/s390/include/asm/diag.h:12,
                 from arch/s390/boot/startup.c:8:
./include/linux/random.h: In function 'add_latent_entropy':
./include/linux/random.h:26:39: error: 'latent_entropy' undeclared
(first use in this function); did you mean 'add_latent_entropy'?
   26 |  add_device_randomness((const void *)&latent_entropy,
      |                                       ^~~~~~~~~~~~~~
      |                                       add_latent_entropy
./include/linux/random.h:26:39: note: each undeclared identifier is
reported only once for each function it appears in

The build error is triggered by commit a80313ff91ab ("s390/kernel:
introduce .dma sections") which made it into 5.2 merge window.

To address that avoid using CONFIG_GCC_PLUGIN_LATENT_ENTROPY in
favour of LATENT_ENTROPY_PLUGIN definition which is defined as a
part of gcc plugins cflags and hence reflect more accurately when gcc
plugin is active. Besides that it is also used for similar purpose in
linux/compiler-gcc.h for latent_entropy attribute definition.

Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
---
 include/linux/random.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/random.h b/include/linux/random.h
index 445a0ea4ff49..d4eb9b3789ad 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -20,7 +20,7 @@ struct random_ready_callback {
 
 extern void add_device_randomness(const void *, unsigned int);
 
-#if defined(CONFIG_GCC_PLUGIN_LATENT_ENTROPY) && !defined(__CHECKER__)
+#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
 static inline void add_latent_entropy(void)
 {
 	add_device_randomness((const void *)&latent_entropy,
-- 
2.18.0.13.gd42ae10