Anton says: In commit 4db7327194 ("powerpc: Add option to use jump
label for cpu_has_feature()") and commit c12e6f24d4 ("powerpc: Add
option to use jump label for mmu_has_feature()") we added:
BUILD_BUG_ON(!__builtin_constant_p(feature))
to cpu_has_feature() and mmu_has_feature() in order to catch usage
issues (such as cpu_has_feature(cpu_has_feature(X), which has happened
once in the past). Unfortunately LLVM isn't smart enough to resolve
this, and it errors out.
I work around it in my clang/LLVM builds of the kernel, but I have just
discovered that it causes a lot of issues for the bcc (eBPF) trace tool
(which uses LLVM).
For now just #ifdef it away for clang builds.
Fixes: 4db7327194 ("powerpc: Add option to use jump label for cpu_has_feature()")
Fixes: c12e6f24d4 ("powerpc: Add option to use jump label for mmu_has_feature()")
Cc: stable@vger.kernel.org # v4.8+
Reported-by: Anton Blanchard <anton@samba.org>
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
The number of CPU feature keys is meant to map 1:1 to the number of CPU
feature flags defined in cputable.h, and the latter must fit in an
unsigned long.
In commit 4db7327194 ("powerpc: Add option to use jump label for
cpu_has_feature()"), I incorrectly defined NUM_CPU_FTR_KEYS to 64.
There should be no real adverse consequences of this bug, other than us
allocating too many keys.
Fix it by using BITS_PER_LONG.
Fixes: 4db7327194 ("powerpc: Add option to use jump label for cpu_has_feature()")
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This allows us to catch incorrect usage of cpu_has_feature() and
mmu_has_feature() prior to jump labels being initialised.
mpe: Use printk() and dump_stack() rather than WARN_ON(), because
WARN_ON() may not work this early in boot. Rename the Kconfig.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
As we just did for CPU features.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
We do binary patching of asm code using CPU features, which is a
one-time operation, done during early boot. However checks of CPU
features in C code are currently done at run time, even though the set
of CPU features can never change after boot.
We can optimise this by using jump labels to implement cpu_has_feature(),
meaning checks in C code are binary patched into a single nop or branch.
For a C sequence along the lines of:
if (cpu_has_feature(FOO))
return 2;
The generated code before is roughly:
ld r9,-27640(r2)
ld r9,0(r9)
lwz r9,32(r9)
cmpwi cr7,r9,0
bge cr7, 1f
li r3,2
blr
1: ...
After (true):
nop
li r3,2
blr
After (false):
b 1f
li r3,2
blr
1: ...
mpe: Rename MAX_CPU_FEATURES as we already have a #define with that
name, and define it simply as a constant, rather than doing tricks with
sizeof and NULL pointers. Rename the array to cpu_feature_keys. Use the
kconfig we added to guard it. Add BUILD_BUG_ON() if the feature is not a
compile time constant. Rewrite the change log.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
We plan to use jump label for cpu_has_feature(). In order to implement
this we need to include the linux/jump_label.h in asm/cputable.h.
Unfortunately if we do that it leads to an include loop. The root of the
problem seems to be that reg.h needs cputable.h (for CPU_FTRs), and then
cputable.h via jump_label.h eventually pulls in hw_irq.h which needs
reg.h (for MSR_EE).
So move cpu_has_feature() to a separate file on its own.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[mpe: Rename to cpu_has_feature.h and flesh out change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Michael Ellerman