linux-kernel - [PATCH 1/2] ARM: add TUSERCOND() macro for conditional postfix

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Date:   Sun,  3 Mar 2019 00:08:18 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     linux@...linux.org.uk
Cc:     ndesaulniers@...gle.com, natechancellor@...il.com, arnd@...db.de,
        ard.biesheuvel@...aro.org, nicolas.pitre@...aro.org,
        thierry.reding@...il.com, will.deacon@....com,
        julien.thierry@....com, mark.rutland@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Stefan Agner <stefan@...er.ch>
Subject: [PATCH 1/2] ARM: add TUSERCOND() macro for conditional postfix

Unified assembly syntax requires conditionals to be postfixes.
TUSER() currently only takes a single argument which then gets
appended t (with translation) on every instruction.

This fixes a build error when using LLVM's integrated assembler:
  In file included from kernel/futex.c:72:
  ./arch/arm/include/asm/futex.h:116:3: error: invalid instruction, did you mean: strt?
          "2:     " TUSER(streq) "        %3, [%4]\n"
           ^
  <inline asm>:5:4: note: instantiated into assembly here
  2:      streqt  r2, [r4]
          ^~~~~~

Additionally, for GCC ".syntax unified" for inline assembly.
When compiling non-Thumb2 GCC always emits a ".syntax divided"
at the beginning of the inline assembly which makes the
assembler fail. Since GCC 5 there is the -masm-syntax-unified
GCC option which make GCC assume unified syntax asm and hence
emits ".syntax unified" even in ARM mode. However, the option
is broken since GCC version 6 (see GCC PR88648 [1]). Work
around by adding ".syntax unified" as part of the inline
assembly.

[0] https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html#index-masm-syntax-unified
[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88648

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
 arch/arm/include/asm/domain.h | 6 ++++--
 arch/arm/include/asm/futex.h  | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/domain.h b/arch/arm/include/asm/domain.h
index 99d9f630d6b6..1888c2d15da5 100644
--- a/arch/arm/include/asm/domain.h
+++ b/arch/arm/include/asm/domain.h
@@ -133,9 +133,11 @@ static inline void modify_domain(unsigned dom, unsigned type)	{ }
  * instructions (inline assembly)
  */
 #ifdef CONFIG_CPU_USE_DOMAINS
-#define TUSER(instr)	#instr "t"
+#define TUSER(instr)		TUSERCOND(instr, )
+#define TUSERCOND(instr, cond)	#instr "t" #cond
 #else
-#define TUSER(instr)	#instr
+#define TUSER(instr)		TUSERCOND(instr, )
+#define TUSERCOND(instr, cond)	#instr #cond
 #endif
 
 #else /* __ASSEMBLY__ */
diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index 0a46676b4245..83c391b597d4 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -110,10 +110,11 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 	preempt_disable();
 	__ua_flags = uaccess_save_and_enable();
 	__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
+	"	.syntax unified\n"
 	"1:	" TUSER(ldr) "	%1, [%4]\n"
 	"	teq	%1, %2\n"
 	"	it	eq	@ explicit IT needed for the 2b label\n"
-	"2:	" TUSER(streq) "	%3, [%4]\n"
+	"2:	" TUSERCOND(str, eq) "	%3, [%4]\n"
 	__futex_atomic_ex_table("%5")
 	: "+r" (ret), "=&r" (val)
 	: "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
-- 
2.20.1