linux-kernel - [PATCH] bcachefs: Fix build on parisc by avoiding _

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Message-ID: <ZbYWI_s05yxbvubr@p100>
Date: Sun, 28 Jan 2024 09:53:55 +0100
From: Helge Deller <deller@...nel.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>,
	linux-bcachefs@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org
Subject: [PATCH] bcachefs: Fix build on parisc by avoiding __multi3()

The gcc compiler on paric does support the __int128 type, although the
architecture does not have native 128-bit support.

The effect is, that the bcachefs u128_square() function will pull in the
libgcc __multi3() helper, which breaks the kernel build when bcachefs is
built as module since this function isn't currently exported in
arch/parisc/kernel/parisc_ksyms.c.
The build failure can be seen in the latest debian kernel build at:
https://buildd.debian.org/status/fetch.php?pkg=linux&arch=hppa&ver=6.7.1-1%7Eexp1&stamp=1706132569&raw=0

We prefer to not export that symbol, so fall back to the optional 64-bit
implementation provided by bcachefs and thus avoid usage of __multi3().

Signed-off-by: Helge Deller <deller@....de>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>

diff --git a/fs/bcachefs/mean_and_variance.h b/fs/bcachefs/mean_and_variance.h
index b2be565bb8f2..64df11ab422b 100644
--- a/fs/bcachefs/mean_and_variance.h
+++ b/fs/bcachefs/mean_and_variance.h
@@ -17,7 +17,7 @@
  * Rust and rustc has issues with u128.
  */

-#if defined(__SIZEOF_INT128__) && defined(__KERNEL__)
+#if defined(__SIZEOF_INT128__) && defined(__KERNEL__) && !defined(CONFIG_PARISC)

 typedef struct {
 	unsigned __int128 v;