On 08/23/2018 05:24 AM, Michael Ellerman wrote:

Hi Breno,

Breno Leitao [off-list ref] writes:

quoted

Function xive_native_get_ipi() might uses chip_id without it being
initialized. This gives the following error on 'smatch' tool:

	error: uninitialized symbol 'chip_id'

Which is correct, it can be used uninitialised. I'm surprised GCC
doesn't warn about it.

quoted

This patch simply sets chip_id initial value to 0.

I'd prefer we fixed it differently, by explicitly initialising to zero
at the appropriate place in the code.

quoted

diff --git a/arch/powerpc/sysdev/xive/native.c b/arch/powerpc/sysdev/xive/native.c
index 311185b9960a..fc56673a3c0f 100644
--- a/arch/powerpc/sysdev/xive/native.c
+++ b/arch/powerpc/sysdev/xive/native.c

@@ -239,7 +239,7 @@ static bool xive_native_match(struct device_node *node)
 static int xive_native_get_ipi(unsigned int cpu, struct xive_cpu *xc)
 {
 	struct device_node *np;
-	unsigned int chip_id;
+	unsigned int chip_id = 0;
 	s64 irq;
 
 	/* Find the chip ID */

The current code is:

	/* Find the chip ID */
	np = of_get_cpu_node(cpu, NULL);
	if (np) {
		if (of_property_read_u32(np, "ibm,chip-id", &chip_id) < 0)
			chip_id = 0;
	}

Where if np is NULL then we don't initialise chip_id.

Which could be:

	np = of_get_cpu_node(cpu, NULL);
        if (of_property_read_u32(np, "ibm,chip-id", &chip_id) < 0)
                chip_id = 0;

Because of_property_read_u32() will just return an error if np is NULL.

It's also missing an of_node_put() of np, you should do a separate patch
to fix that. You can just do it unconditionally after the
of_property_read_u32().

I think we can simply get rid of the OF code under xive_native_get_ipi()
and use xc->chip_id instead. It should be safe to use as xive_prepare_cpu() 
should have initialized ->chip_id by the time xive_native_get_ipi() is 
called. 

Cheers,

C.