linux-kernel - [PATCH 4.19 008/234] latent_entropy: avoid build error when plugin cflags are not set

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Date:   Thu, 23 Jun 2022 18:41:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 4.19 008/234] latent_entropy: avoid build error when plugin cflags are not set

From: Vasily Gorbik <gor@...ux.ibm.com>

commit 7e756f423af808b6571fed3144747db2ef7fa1c5 upstream.

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>
Acked-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/linux/random.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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,