[PATCH] MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC

[PATCH] MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC

[Maciej W. Rozycki]

Fix a build regression from commit c9017757c532 ("MIPS: init upper 64b 
of vector registers when MSA is first used"):

arch/mips/built-in.o: In function `enable_restore_fp_context':
traps.c:(.text+0xbb90): undefined reference to `_init_msa_upper'
traps.c:(.text+0xbb90): relocation truncated to fit: R_MIPS_26 against `_init_msa_upper'
traps.c:(.text+0xbef0): undefined reference to `_init_msa_upper'
traps.c:(.text+0xbef0): relocation truncated to fit: R_MIPS_26 against `_init_msa_upper'

to !CONFIG_CPU_HAS_MSA configurations with older GCC versions, which are 
unable to figure out that calls to `_init_msa_upper' are indeed dead.
Of the many ways to tackle this failure choose the approach we have 
already taken in `thread_msa_context_live'.

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: stable@vger.kernel.org # v3.16+
---
 I have verified that this patch removes the build failure and if applied 
to a build made with a newer version of GCC which copes regardless it 
makes no change to code generated in a !CONFIG_CPU_HAS_MSA configuration, 
and in a CONFIG_CPU_HAS_MSA one it only makes this change (haha):

--- a/vmlinux.dump	2016-05-17 01:01:03.655891000 +0100
+++ b/vmlinux.dump	2016-05-17 02:11:49.264564000 +0100
@@ -12880,7 +12880,7 @@
 8400cdf4 <enable_restore_fp_context+0x414> 00031e82 	srl	v1,v1,0x1a
 8400cdf8 <enable_restore_fp_context+0x418> 38630001 	xori	v1,v1,0x1
 8400cdfc <enable_restore_fp_context+0x41c> 30630001 	andi	v1,v1,0x1
-8400ce00 <enable_restore_fp_context+0x420> 10e300ea 	beq	a3,v1,8400d1ac <enable_restore_fp_context+0x7cc>
+8400ce00 <enable_restore_fp_context+0x420> 106700ea 	beq	v1,a3,8400d1ac <enable_restore_fp_context+0x7cc>
 8400ce04 <enable_restore_fp_context+0x424> 3c062000 	lui	a2,0x2000
 8400ce08 <enable_restore_fp_context+0x428> 8c430000 	lw	v1,0(v0)
 8400ce0c <enable_restore_fp_context+0x42c> 30a50001 	andi	a1,a1,0x1

Therefore please apply and backport as applicable.

  Maciej

linux-mips-init-msa-upper.diff
Index: linux-sfr-msa/arch/mips/include/asm/msa.h
===================================================================
--- linux-sfr-msa.orig/arch/mips/include/asm/msa.h	2016-05-17 01:53:09.316108000 +0100
+++ linux-sfr-msa/arch/mips/include/asm/msa.h	2016-05-17 01:54:29.684642000 +0100
@@ -147,6 +147,19 @@ static inline void restore_msa(struct ta
 		_restore_msa(t);
 }
 
+static inline void init_msa_upper(void)
+{
+	/*
+	 * Check cpu_has_msa only if it's a constant. This will allow the
+	 * compiler to optimise out code for CPUs without MSA without adding
+	 * an extra redundant check for CPUs with MSA.
+	 */
+	if (__builtin_constant_p(cpu_has_msa) && !cpu_has_msa)
+		return;
+
+	_init_msa_upper();
+}
+
 #ifdef TOOLCHAIN_SUPPORTS_MSA
 
 #define __BUILD_MSA_CTL_REG(name, cs)				\
Index: linux-sfr-msa/arch/mips/kernel/traps.c
===================================================================
--- linux-sfr-msa.orig/arch/mips/kernel/traps.c	2016-05-17 01:53:09.319110000 +0100
+++ linux-sfr-msa/arch/mips/kernel/traps.c	2016-05-17 01:54:29.711642000 +0100
@@ -1246,7 +1246,7 @@ static int enable_restore_fp_context(int
 		err = init_fpu();
 		if (msa && !err) {
 			enable_msa();
-			_init_msa_upper();
+			init_msa_upper();
 			set_thread_flag(TIF_USEDMSA);
 			set_thread_flag(TIF_MSA_CTX_LIVE);
 		}
@@ -1309,7 +1309,7 @@ static int enable_restore_fp_context(int
 	 */
 	prior_msa = test_and_set_thread_flag(TIF_MSA_CTX_LIVE);
 	if (!prior_msa && was_fpu_owner) {
-		_init_msa_upper();
+		init_msa_upper();
 
 		goto out;
 	}
@@ -1326,7 +1326,7 @@ static int enable_restore_fp_context(int
 		 * of each vector register such that it cannot see data left
 		 * behind by another task.
 		 */
-		_init_msa_upper();
+		init_msa_upper();
 	} else {
 		/* We need to restore the vector context. */
 		restore_msa(current);

[PATCH] MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC

[Maciej W. Rozycki]

Fix a build regression from commit c9017757c532 ("MIPS: init upper 64b 
of vector registers when MSA is first used"):

arch/mips/built-in.o: In function `enable_restore_fp_context':
traps.c:(.text+0xbb90): undefined reference to `_init_msa_upper'
traps.c:(.text+0xbb90): relocation truncated to fit: R_MIPS_26 against `_init_msa_upper'
traps.c:(.text+0xbef0): undefined reference to `_init_msa_upper'
traps.c:(.text+0xbef0): relocation truncated to fit: R_MIPS_26 against `_init_msa_upper'

to !CONFIG_CPU_HAS_MSA configurations with older GCC versions, which are 
unable to figure out that calls to `_init_msa_upper' are indeed dead.
Of the many ways to tackle this failure choose the approach we have 
already taken in `thread_msa_context_live'.

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: stable@vger.kernel.org # v3.16+
---
 I have verified that this patch removes the build failure and if applied 
to a build made with a newer version of GCC which copes regardless it 
makes no change to code generated in a !CONFIG_CPU_HAS_MSA configuration, 
and in a CONFIG_CPU_HAS_MSA one it only makes this change (haha):

--- a/vmlinux.dump	2016-05-17 01:01:03.655891000 +0100
+++ b/vmlinux.dump	2016-05-17 02:11:49.264564000 +0100
@@ -12880,7 +12880,7 @@
 8400cdf4 <enable_restore_fp_context+0x414> 00031e82 	srl	v1,v1,0x1a
 8400cdf8 <enable_restore_fp_context+0x418> 38630001 	xori	v1,v1,0x1
 8400cdfc <enable_restore_fp_context+0x41c> 30630001 	andi	v1,v1,0x1
-8400ce00 <enable_restore_fp_context+0x420> 10e300ea 	beq	a3,v1,8400d1ac <enable_restore_fp_context+0x7cc>
+8400ce00 <enable_restore_fp_context+0x420> 106700ea 	beq	v1,a3,8400d1ac <enable_restore_fp_context+0x7cc>
 8400ce04 <enable_restore_fp_context+0x424> 3c062000 	lui	a2,0x2000
 8400ce08 <enable_restore_fp_context+0x428> 8c430000 	lw	v1,0(v0)
 8400ce0c <enable_restore_fp_context+0x42c> 30a50001 	andi	a1,a1,0x1

Therefore please apply and backport as applicable.

  Maciej

linux-mips-init-msa-upper.diff
Index: linux-sfr-msa/arch/mips/include/asm/msa.h
===================================================================
--- linux-sfr-msa.orig/arch/mips/include/asm/msa.h	2016-05-17 01:53:09.316108000 +0100
+++ linux-sfr-msa/arch/mips/include/asm/msa.h	2016-05-17 01:54:29.684642000 +0100
@@ -147,6 +147,19 @@ static inline void restore_msa(struct ta
 		_restore_msa(t);
 }
 
+static inline void init_msa_upper(void)
+{
+	/*
+	 * Check cpu_has_msa only if it's a constant. This will allow the
+	 * compiler to optimise out code for CPUs without MSA without adding
+	 * an extra redundant check for CPUs with MSA.
+	 */
+	if (__builtin_constant_p(cpu_has_msa) && !cpu_has_msa)
+		return;
+
+	_init_msa_upper();
+}
+
 #ifdef TOOLCHAIN_SUPPORTS_MSA
 
 #define __BUILD_MSA_CTL_REG(name, cs)				\
Index: linux-sfr-msa/arch/mips/kernel/traps.c
===================================================================
--- linux-sfr-msa.orig/arch/mips/kernel/traps.c	2016-05-17 01:53:09.319110000 +0100
+++ linux-sfr-msa/arch/mips/kernel/traps.c	2016-05-17 01:54:29.711642000 +0100
@@ -1246,7 +1246,7 @@ static int enable_restore_fp_context(int
 		err = init_fpu();
 		if (msa && !err) {
 			enable_msa();
-			_init_msa_upper();
+			init_msa_upper();
 			set_thread_flag(TIF_USEDMSA);
 			set_thread_flag(TIF_MSA_CTX_LIVE);
 		}
@@ -1309,7 +1309,7 @@ static int enable_restore_fp_context(int
 	 */
 	prior_msa = test_and_set_thread_flag(TIF_MSA_CTX_LIVE);
 	if (!prior_msa && was_fpu_owner) {
-		_init_msa_upper();
+		init_msa_upper();
 
 		goto out;
 	}
@@ -1326,7 +1326,7 @@ static int enable_restore_fp_context(int
 		 * of each vector register such that it cannot see data left
 		 * behind by another task.
 		 */
-		_init_msa_upper();
+		init_msa_upper();
 	} else {
 		/* We need to restore the vector context. */
 		restore_msa(current);

Re: [PATCH] MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC

[Ralf Baechle]

On Tue, May 17, 2016 at 06:12:27AM +0100, Maciej W. Rozycki wrote:

> --- a/vmlinux.dump	2016-05-17 01:01:03.655891000 +0100
> +++ b/vmlinux.dump	2016-05-17 02:11:49.264564000 +0100

Applied with this junk segment dropped.

  Ralf

Re: [PATCH] MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC

[Maciej W. Rozycki]

On Tue, 17 May 2016, Ralf Baechle wrote:

> > --- a/vmlinux.dump	2016-05-17 01:01:03.655891000 +0100
> > +++ b/vmlinux.dump	2016-05-17 02:11:49.264564000 +0100
> 
> Applied with this junk segment dropped.

 Ah, I didn't realise it would confuse `git am' -- otherwise I would have 
escaped it or mangled somehow.  Thanks for taking care of it then.

  Maciej

Re: [PATCH] MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC

[Maciej W. Rozycki]

On Tue, 17 May 2016, Ralf Baechle wrote:

> > --- a/vmlinux.dump	2016-05-17 01:01:03.655891000 +0100
> > +++ b/vmlinux.dump	2016-05-17 02:11:49.264564000 +0100
> 
> Applied with this junk segment dropped.

 Ah, I didn't realise it would confuse `git am' -- otherwise I would have 
escaped it or mangled somehow.  Thanks for taking care of it then.

  Maciej