Patch "MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mips-msa-fix-a-link-error-on-_init_msa_upper-with-older-gcc.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Maciej W. Rozycki" <[email protected]>
Date: Tue, 17 May 2016 06:12:27 +0100
Subject: MIPS: MSA: Fix a link error on `_init_msa_upper' with older GCC

From: Maciej W. Rozycki <[email protected]>

commit e49d38488515057dba8f0c2ba4cfde5be4a7281f upstream.

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'.

[[email protected]: Drop patch segment to junk file.]

Patchwork: https://patchwork.linux-mips.org/patch/13271/

---
 arch/mips/include/asm/msa.h |   13 +++++++++++++
 arch/mips/kernel/traps.c    |    6 +++---
 2 files changed, 16 insertions(+), 3 deletions(-)

@@ -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)				\

@@ -1242,7 +1242,7 @@ 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);
 		}

@@ -1305,7 +1305,7 @@ 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;
 	}

@@ -1322,7 +1322,7 @@ 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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/mips-msa-fix-a-link-error-on-_init_msa_upper-with-older-gcc.patch queue-4.5/mips-math-emu-fix-jalr-emulation-when-rd-0.patch