[PATCH] clk: fix false-positive Wmaybe-uninitialized warning

[PATCH] clk: fix false-positive Wmaybe-uninitialized warning

[Arnd Bergmann]

When we build this driver with on x86-32, gcc produces a false-positive warning:

drivers/clk/renesas/clk-sh73a0.c: In function 'sh73a0_cpg_clocks_init':
drivers/clk/renesas/clk-sh73a0.c:155:10: error: 'parent_name' may be used uninitialized in this function [-Werror=maybe-uninitialized]
   return clk_register_fixed_factor(NULL, name, parent_name, 0,

We can work around that warning by adding a fake initialization, I tried
and failed to come up with any better workaround. This is currently one
of few remaining warnings for a 4.14.y randconfig build, so it would be
good to also have it backported at least to that version. Older versions
have more randconfig warnings, so we might not care.

I had not noticed this earlier, because one patch in my randconfig test
tree removes the '-ffreestanding' option on x86-32, and that avoids
the warning. The -ffreestanding flag was originally global but moved
into arch/i386 by Andi Kleen in commit 6edfba1b33c7 ("[PATCH] x86_64:
Don't define string functions to builtin") as a 'temporary workaround'.

Like many temporary hacks, this turned out to be rather long-lived, from
all I can tell we still need a simple fix to asm/string_32.h before it
can be removed, but I'm not sure about how to best do that.

Cc: stable@vger.kernel.org
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/clk/renesas/clk-sh73a0.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/renesas/clk-sh73a0.c b/drivers/clk/renesas/clk-sh73a0.c
index eea38f6ea77e..3892346c4fcc 100644
--- a/drivers/clk/renesas/clk-sh73a0.c
+++ b/drivers/clk/renesas/clk-sh73a0.c
@@ -46,7 +46,7 @@ struct div4_clk {
 	unsigned int shift;
 };
 
-static struct div4_clk div4_clks[] = {
+static const struct div4_clk div4_clks[] = {
 	{ "zg", "pll0", CPG_FRQCRA, 16 },
 	{ "m3", "pll1", CPG_FRQCRA, 12 },
 	{ "b",  "pll1", CPG_FRQCRA,  8 },
@@ -79,7 +79,7 @@ sh73a0_cpg_register_clock(struct device_node *np, struct sh73a0_cpg *cpg,
 {
 	const struct clk_div_table *table = NULL;
 	unsigned int shift, reg, width;
-	const char *parent_name;
+	const char *parent_name = NULL;
 	unsigned int mult = 1;
 	unsigned int div = 1;
 
@@ -135,7 +135,7 @@ sh73a0_cpg_register_clock(struct device_node *np, struct sh73a0_cpg *cpg,
 		shift = 24;
 		width = 5;
 	} else {
-		struct div4_clk *c;
+		const struct div4_clk *c;
 
 		for (c = div4_clks; c->name; c++) {
 			if (!strcmp(name, c->name)) {
-- 
2.9.0

Re: [PATCH] clk: fix false-positive Wmaybe-uninitialized warning

[Geert Uytterhoeven]

Hi Arnd,

On Fri, Feb 16, 2018 at 4:27 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> When we build this driver with on x86-32, gcc produces a false-positive warning:
>
> drivers/clk/renesas/clk-sh73a0.c: In function 'sh73a0_cpg_clocks_init':
> drivers/clk/renesas/clk-sh73a0.c:155:10: error: 'parent_name' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    return clk_register_fixed_factor(NULL, name, parent_name, 0,
>
> We can work around that warning by adding a fake initialization, I tried
> and failed to come up with any better workaround. This is currently one
> of few remaining warnings for a 4.14.y randconfig build, so it would be
> good to also have it backported at least to that version. Older versions
> have more randconfig warnings, so we might not care.
>
> I had not noticed this earlier, because one patch in my randconfig test
> tree removes the '-ffreestanding' option on x86-32, and that avoids
> the warning. The -ffreestanding flag was originally global but moved
> into arch/i386 by Andi Kleen in commit 6edfba1b33c7 ("[PATCH] x86_64:
> Don't define string functions to builtin") as a 'temporary workaround'.
>
> Like many temporary hacks, this turned out to be rather long-lived, from
> all I can tell we still need a simple fix to asm/string_32.h before it
> can be removed, but I'm not sure about how to best do that.
>
> Cc: stable@vger.kernel.org
> Cc: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks, this is a known false positive.

Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>

> ---
>  drivers/clk/renesas/clk-sh73a0.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/renesas/clk-sh73a0.c b/drivers/clk/renesas/clk-sh73a0.c
> index eea38f6ea77e..3892346c4fcc 100644
> --- a/drivers/clk/renesas/clk-sh73a0.c
> +++ b/drivers/clk/renesas/clk-sh73a0.c
> @@ -46,7 +46,7 @@ struct div4_clk {
>         unsigned int shift;
>  };
>
> -static struct div4_clk div4_clks[] = {
> +static const struct div4_clk div4_clks[] = {

This change is not part of the fix...

>         { "zg", "pll0", CPG_FRQCRA, 16 },
>         { "m3", "pll1", CPG_FRQCRA, 12 },
>         { "b",  "pll1", CPG_FRQCRA,  8 },
> @@ -79,7 +79,7 @@ sh73a0_cpg_register_clock(struct device_node *np, struct sh73a0_cpg *cpg,
>  {
>         const struct clk_div_table *table = NULL;
>         unsigned int shift, reg, width;
> -       const char *parent_name;
> +       const char *parent_name = NULL;
>         unsigned int mult = 1;
>         unsigned int div = 1;
>
> @@ -135,7 +135,7 @@ sh73a0_cpg_register_clock(struct device_node *np, struct sh73a0_cpg *cpg,
>                 shift = 24;
>                 width = 5;
>         } else {
> -               struct div4_clk *c;
> +               const struct div4_clk *c;

... and neither is this one.

>
>                 for (c = div4_clks; c->name; c++) {
>                         if (!strcmp(name, c->name)) {

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] clk: fix false-positive Wmaybe-uninitialized warning

[Stephen Boyd]

Quoting Arnd Bergmann (2018-02-16 07:27:47)
> When we build this driver with on x86-32, gcc produces a false-positive warning:
> 
> drivers/clk/renesas/clk-sh73a0.c: In function 'sh73a0_cpg_clocks_init':
> drivers/clk/renesas/clk-sh73a0.c:155:10: error: 'parent_name' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    return clk_register_fixed_factor(NULL, name, parent_name, 0,
> 
> We can work around that warning by adding a fake initialization, I tried
> and failed to come up with any better workaround. This is currently one
> of few remaining warnings for a 4.14.y randconfig build, so it would be
> good to also have it backported at least to that version. Older versions
> have more randconfig warnings, so we might not care.
> 
> I had not noticed this earlier, because one patch in my randconfig test
> tree removes the '-ffreestanding' option on x86-32, and that avoids
> the warning. The -ffreestanding flag was originally global but moved
> into arch/i386 by Andi Kleen in commit 6edfba1b33c7 ("[PATCH] x86_64:
> Don't define string functions to builtin") as a 'temporary workaround'.
> 
> Like many temporary hacks, this turned out to be rather long-lived, from
> all I can tell we still need a simple fix to asm/string_32.h before it
> can be removed, but I'm not sure about how to best do that.
> 
> Cc: stable@vger.kernel.org
> Cc: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---

Applied to clk-next