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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 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);
