| Message ID | 20220920152935.1569605-1-yury.norov@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | powerpc/64: don't refer nr_cpu_ids in asm code when it's undefined | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/github-powerpc_ppctests | success | Successfully ran 10 jobs. |
| snowpatch_ozlabs/github-powerpc_selftests | success | Successfully ran 10 jobs. |
| snowpatch_ozlabs/github-powerpc_clang | success | Successfully ran 6 jobs. |
| snowpatch_ozlabs/github-powerpc_kernel_qemu | success | Successfully ran 23 jobs. |
| snowpatch_ozlabs/github-powerpc_sparse | success | Successfully ran 4 jobs. |
Hi Yury, On Tue, 20 Sep 2022 08:29:35 -0700 Yury Norov <yury.norov@gmail.com> wrote: > > diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S > index cf2c08902c05..7cb97881635e 100644 > --- a/arch/powerpc/kernel/head_64.S > +++ b/arch/powerpc/kernel/head_64.S > @@ -400,7 +400,11 @@ generic_secondary_common_init: > #else > LOAD_REG_ADDR(r8, paca_ptrs) /* Load paca_ptrs pointe */ > ld r8,0(r8) /* Get base vaddr of array */ > +#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS) > + LOAD_REG_IMMEDIATE(r7, NR_CPUS) > +#else > LOAD_REG_ADDR(r7, nr_cpu_ids) /* Load nr_cpu_ids address */ > +#endif > lwz r7,0(r7) /* also the max paca allocated */ > li r5,0 /* logical cpu id */ > 1: > -- > 2.34.1 > I don't know PPC assembly very well, but should the #endif be one line lower so that the constant is not dereferenced in the non-#else case?
On Wed, Sep 21, 2022 at 08:20:06AM +1000, Stephen Rothwell wrote: > Hi Yury, > > On Tue, 20 Sep 2022 08:29:35 -0700 Yury Norov <yury.norov@gmail.com> wrote: > > > > > diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S > > index cf2c08902c05..7cb97881635e 100644 > > --- a/arch/powerpc/kernel/head_64.S > > +++ b/arch/powerpc/kernel/head_64.S > > @@ -400,7 +400,11 @@ generic_secondary_common_init: > > #else > > LOAD_REG_ADDR(r8, paca_ptrs) /* Load paca_ptrs pointe */ > > ld r8,0(r8) /* Get base vaddr of array */ > > +#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS) > > + LOAD_REG_IMMEDIATE(r7, NR_CPUS) > > +#else > > LOAD_REG_ADDR(r7, nr_cpu_ids) /* Load nr_cpu_ids address */ > > +#endif > > lwz r7,0(r7) /* also the max paca allocated */ > > li r5,0 /* logical cpu id */ > > 1: > > -- > > 2.34.1 > > > > I don't know PPC assembly very well, but should the #endif be one line > lower so that the constant is not dereferenced in the non-#else case? Looks like you're right. Thanks, I'll send a v2.
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S index cf2c08902c05..7cb97881635e 100644 --- a/arch/powerpc/kernel/head_64.S +++ b/arch/powerpc/kernel/head_64.S @@ -400,7 +400,11 @@ generic_secondary_common_init: #else LOAD_REG_ADDR(r8, paca_ptrs) /* Load paca_ptrs pointe */ ld r8,0(r8) /* Get base vaddr of array */ +#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS) + LOAD_REG_IMMEDIATE(r7, NR_CPUS) +#else LOAD_REG_ADDR(r7, nr_cpu_ids) /* Load nr_cpu_ids address */ +#endif lwz r7,0(r7) /* also the max paca allocated */ li r5,0 /* logical cpu id */ 1:
generic_secondary_common_init() calls LOAD_REG_ADDR(r7, nr_cpu_ids) conditionally on CONFIG_SMP. However, if NR_CPUS == 1, kernel doesn't use the nr_cpu_ids, and in C code, it's just: #if NR_CPUS == 1 #define nr_cpu_ids ... The [1] makes declaration of nr_cpu_ids conditional on NR_CPUS == 1, and that reveals the issue: compiler can't link the LOAD_REG_ADDR(r7, nr_cpu_ids) against nonexisting symbol. Current code looks unsafe for those who build kernel with CONFIG_SMP=y and NR_CPUS == 1. This is weird configuration, but not disallowed. Fix the linker error by replacing LOAD_REG_ADDR() with LOAD_REG_IMMEDIATE() conditionally on NR_CPUS == 1. The issue was spotted after applying [1], which adds a CONFIG_FORCE_NR_CPUS option that has the similar effect on nr_cpu_ids. So, in this patch, make the LOAD_REG() conditional on CONFIG_FORCE_NR_CPUS too. On top of: [1] https://lore.kernel.org/lkml/20220905230820.3295223-4-yury.norov@gmail.com/T/#m96ffe122721893471fd3470d911a8f2fad6d03b3 Reported-by: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Yury Norov <yury.norov@gmail.com> --- arch/powerpc/kernel/head_64.S | 4 ++++ 1 file changed, 4 insertions(+)