linux-kernel - Re: [PATCH v4 5/6] add listmount(2) syscall

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Message-ID: <ab4e88fa-af6a-49e9-a8bc-3cdc3a531aaf@roeck-us.net>
Date: Thu, 11 Jan 2024 21:24:25 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Rich Felker <dalias@...c.org>,
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	Miklos Szeredi <mszeredi@...hat.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-man@...r.kernel.org, linux-security-module@...r.kernel.org,
	Karel Zak <kzak@...hat.com>, Ian Kent <raven@...maw.net>,
	David Howells <dhowells@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <christian@...uner.io>,
	Amir Goldstein <amir73il@...il.com>,
	Matthew House <mattlloydhouse@...il.com>,
	Florian Weimer <fweimer@...hat.com>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v4 5/6] add listmount(2) syscall

On Thu, Jan 11, 2024 at 07:40:32PM -0800, Linus Torvalds wrote:
> On Thu, 11 Jan 2024 at 15:57, Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > I wonder if something may be wrong with the definition and use of __m
> > for u64 accesses. The code below also fixes the build problem.
> 
> Ok, that looks like the right workaround.
> 

I think I'll go with the code below. It doesn't touch the MMU code
(which for some reason doesn't result in a build failure), and
it generates

! 5071 "fs/namespace.c" 1
        mov.l   r6,@r1
        mov.l   r7,@(4,r1)

which seems to be correct. It also matches the pattern used
for __put_user_asm(). Does that make sense ?

Thanks,
Guenter

---
diff --git a/arch/sh/include/asm/uaccess_32.h b/arch/sh/include/asm/uaccess_32.h
index 5d7ddc092afd..5ce46b2a95b6 100644
--- a/arch/sh/include/asm/uaccess_32.h
+++ b/arch/sh/include/asm/uaccess_32.h
@@ -176,6 +176,7 @@ do {							\
 } while (0)
 #endif /* CONFIG_MMU */
 
+#ifdef CONFIG_MMU
 #if defined(CONFIG_CPU_LITTLE_ENDIAN)
 #define __put_user_u64(val,addr,retval) \
 ({ \
@@ -221,6 +222,26 @@ __asm__ __volatile__( \
 	: "r" (val), "m" (__m(addr)), "i" (-EFAULT), "0" (retval) \
         : "memory"); })
 #endif
+#else
+#if defined(CONFIG_CPU_LITTLE_ENDIAN)
+#define __put_user_u64(val,addr,retval) \
+({ \
+__asm__ __volatile__( \
+	"mov.l	%R0,%1\n\t" \
+	"mov.l	%S0,%T1\n\t" \
+	: /* no outputs */ \
+	: "r" (val), "m" (*(u64 *)(addr)) \
+	: "memory"); })
+#else
+({ \
+__asm__ __volatile__( \
+	"mov.l	%S0,%1\n\t" \
+	"mov.l	%R0,%T1\n\t" \
+	: /* no outputs */ \
+	: "r" (val), "m" (*(u64 *)(addr)) \
+	: "memory"); })
+#endif
+#endif /* CONFIG_MMU */
 
 extern void __put_user_unknown(void);