[PATCH] s390: add unreachable() to dump_fault_info() to fix -Wmaybe-uninitialized

[PATCH] s390: add unreachable() to dump_fault_info() to fix -Wmaybe-uninitialized

[Masahiro Yamada]

When CONFIG_OPTIMIZE_INLINING is enabled for s390, I see this warning:

arch/s390/mm/fault.c:127:15: warning: 'asce' may be used uninitialized in this function [-Wmaybe-uninitialized]
  switch (asce & _ASCE_TYPE_MASK) {
arch/s390/mm/fault.c:177:16: note: 'asce' was declared here
  unsigned long asce;
                ^~~~

If get_fault_type() is not inlined, the compiler cannot deduce that
all the possible paths in the 'switch' statement are covered.

Of course, we could mark get_fault_type() as __always_inline to get
back the original behavior, but I do not think it sensible to force
inlining just for the purpose of suppressing the warning. Since this
is just a matter of warning, I want to keep as much room for compiler
optimization as possible.

I added unreachable() to teach the compiler that the 'default' label
is unreachable.

I got rid of the 'inline' marker. Even without the 'inline' hint,
the compiler inlines functions based on its inlining heuristic.

Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

 arch/s390/mm/fault.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index c220399ae196..91ce03fd0c84 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -85,7 +85,7 @@ static inline int notify_page_fault(struct pt_regs *regs)
  * Find out which address space caused the exception.
  * Access register mode is impossible, ignore space == 3.
  */
-static inline enum fault_type get_fault_type(struct pt_regs *regs)
+static enum fault_type get_fault_type(struct pt_regs *regs)
 {
 	unsigned long trans_exc_code;
 
@@ -211,6 +211,8 @@ static void dump_fault_info(struct pt_regs *regs)
 		asce = S390_lowcore.kernel_asce;
 		pr_cont("kernel ");
 		break;
+	default:
+		unreachable();
 	}
 	pr_cont("ASCE.\n");
 	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
-- 
2.17.1

Re: [PATCH] s390: add unreachable() to dump_fault_info() to fix -Wmaybe-uninitialized

[Sergey Senozhatsky]

On (05/17/19 15:49), Masahiro Yamada wrote:
[..]
> @@ -211,6 +211,8 @@ static void dump_fault_info(struct pt_regs *regs)
>  		asce = S390_lowcore.kernel_asce;
>  		pr_cont("kernel ");
>  		break;
> +	default:
> +		unreachable();
>  	}
>  	pr_cont("ASCE.\n");
>  	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);

Or have default fault type and asce?

Just an idea.

---

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index c220399ae196..876d71c31894 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -174,7 +174,8 @@ static void dump_pagetable(unsigned long asce, unsigned long address)
 
 static void dump_fault_info(struct pt_regs *regs)
 {
-	unsigned long asce;
+	unsigned long asce = S390_lowcore.kernel_asce;
+	char *type = "kernel ";
 
 	pr_alert("Failing address: %016lx TEID: %016lx\n",
 		 regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
@@ -197,22 +198,18 @@ static void dump_fault_info(struct pt_regs *regs)
 	switch (get_fault_type(regs)) {
 	case USER_FAULT:
 		asce = S390_lowcore.user_asce;
-		pr_cont("user ");
+		type = "user ";
 		break;
 	case VDSO_FAULT:
 		asce = S390_lowcore.vdso_asce;
-		pr_cont("vdso ");
+		type = "vdso ";
 		break;
 	case GMAP_FAULT:
 		asce = ((struct gmap *) S390_lowcore.gmap)->asce;
-		pr_cont("gmap ");
-		break;
-	case KERNEL_FAULT:
-		asce = S390_lowcore.kernel_asce;
-		pr_cont("kernel ");
+		type = "gmap ";
 		break;
 	}
-	pr_cont("ASCE.\n");
+	pr_cont("%s ASCE.\n", type);
 	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
 }
 

Re: [PATCH] s390: add unreachable() to dump_fault_info() to fix -Wmaybe-uninitialized

[Martin Schwidefsky]

On Fri, 17 May 2019 15:49:22 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> When CONFIG_OPTIMIZE_INLINING is enabled for s390, I see this warning:
> 
> arch/s390/mm/fault.c:127:15: warning: 'asce' may be used uninitialized in this function [-Wmaybe-uninitialized]
>   switch (asce & _ASCE_TYPE_MASK) {
> arch/s390/mm/fault.c:177:16: note: 'asce' was declared here
>   unsigned long asce;
>                 ^~~~
> 
> If get_fault_type() is not inlined, the compiler cannot deduce that
> all the possible paths in the 'switch' statement are covered.
> 
> Of course, we could mark get_fault_type() as __always_inline to get
> back the original behavior, but I do not think it sensible to force
> inlining just for the purpose of suppressing the warning. Since this
> is just a matter of warning, I want to keep as much room for compiler
> optimization as possible.
> 
> I added unreachable() to teach the compiler that the 'default' label
> is unreachable.
> 
> I got rid of the 'inline' marker. Even without the 'inline' hint,
> the compiler inlines functions based on its inlining heuristic.
> 
> Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING")
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Added to our internal tree and I will add it to s390/linux soon. Thanks.

> ---
> 
>  arch/s390/mm/fault.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index c220399ae196..91ce03fd0c84 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -85,7 +85,7 @@ static inline int notify_page_fault(struct pt_regs *regs)
>   * Find out which address space caused the exception.
>   * Access register mode is impossible, ignore space == 3.
>   */
> -static inline enum fault_type get_fault_type(struct pt_regs *regs)
> +static enum fault_type get_fault_type(struct pt_regs *regs)
>  {
>  	unsigned long trans_exc_code;
> 
> @@ -211,6 +211,8 @@ static void dump_fault_info(struct pt_regs *regs)
>  		asce = S390_lowcore.kernel_asce;
>  		pr_cont("kernel ");
>  		break;
> +	default:
> +		unreachable();
>  	}
>  	pr_cont("ASCE.\n");
>  	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);


-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.