[PATCH v2] PCI: dwc: Fix W=1 build warning in dw_pcie_edma_irq_verify()

[PATCH v2] PCI: dwc: Fix W=1 build warning in dw_pcie_edma_irq_verify()

[Niklas Cassel]

Change dw_pcie_edma_irq_verify() to print the dma channel as %u.

While a DWC glue driver could theoretically initialize nr_irqs to a
negative value, doing so would obviously be incorrect, and the later
dw_edma_probe(struct dw_edma_chip *chip) call would fail, since while
the dw_edma_probe() call expects the caller to initialize chip->nr_irqs,
dw_edma_probe() verifies nr_irqs and returns failure if nr_irqs is < 1.

This fixes the following build warning when compiling with W=1:

drivers/pci/controller/dwc/pcie-designware.c: In function ‘dw_pcie_edma_detect’:
drivers/pci/controller/dwc/pcie-designware.c:989:50: warning: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 3 [-Wformat-truncation=]
  989 |                 snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
      |                                                  ^~

Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Changes since V1:
-Do not reject negative nr_irqs value in dw_pcie_edma_irq_verify(),
 as this will already be done by dw_edma_probe().

 drivers/pci/controller/dwc/pcie-designware.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index 3c683b6119c3..0a13fb4336f4 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -986,7 +986,7 @@ static int dw_pcie_edma_irq_verify(struct dw_pcie *pci)
 	}
 
 	for (; pci->edma.nr_irqs < ch_cnt; pci->edma.nr_irqs++) {
-		snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
+		snprintf(name, sizeof(name), "dma%u", pci->edma.nr_irqs);
 
 		ret = platform_get_irq_byname_optional(pdev, name);
 		if (ret <= 0)
-- 
2.47.1

Re: [PATCH v2] PCI: dwc: Fix W=1 build warning in dw_pcie_edma_irq_verify()

[Bjorn Helgaas]

Can you make the subject say something about the fix instead of the
warning?  E.g., something about fixing a potential truncation?

On Thu, Jan 02, 2025 at 12:13:40PM +0100, Niklas Cassel wrote:
> Change dw_pcie_edma_irq_verify() to print the dma channel as %u.
> 
> While a DWC glue driver could theoretically initialize nr_irqs to a
> negative value, doing so would obviously be incorrect, and the later
> dw_edma_probe(struct dw_edma_chip *chip) call would fail, since while
> the dw_edma_probe() call expects the caller to initialize chip->nr_irqs,
> dw_edma_probe() verifies nr_irqs and returns failure if nr_irqs is < 1.
> 
> This fixes the following build warning when compiling with W=1:
> 
> drivers/pci/controller/dwc/pcie-designware.c: In function ‘dw_pcie_edma_detect’:
> drivers/pci/controller/dwc/pcie-designware.c:989:50: warning: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 3 [-Wformat-truncation=]
>   989 |                 snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
>       |                                                  ^~
> 
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
> Changes since V1:
> -Do not reject negative nr_irqs value in dw_pcie_edma_irq_verify(),
>  as this will already be done by dw_edma_probe().
> 
>  drivers/pci/controller/dwc/pcie-designware.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 3c683b6119c3..0a13fb4336f4 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -986,7 +986,7 @@ static int dw_pcie_edma_irq_verify(struct dw_pcie *pci)
>  	}
>  
>  	for (; pci->edma.nr_irqs < ch_cnt; pci->edma.nr_irqs++) {
> -		snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
> +		snprintf(name, sizeof(name), "dma%u", pci->edma.nr_irqs);

I don't understand this fix.  I guess the warning is complaining that
sizeof(name) == 6, and "dma" takes up three bytes, so the %d has to
fit in the remaining region of size 3?

But I don't see how printing nr_irqs as unsigned rather than signed is
a fix, since even an unsigned int can be longer than 3 digits.

And I don't like using "%u" for a signed value in order to "fix"
something.  That's asking for a future cleanup to revert the change.

What's wrong with just making the name[] buffer big enough?

>  		ret = platform_get_irq_byname_optional(pdev, name);
>  		if (ret <= 0)
> -- 
> 2.47.1
> 

Re: [PATCH v2] PCI: dwc: Fix W=1 build warning in dw_pcie_edma_irq_verify()

[Niklas Cassel]

On Fri, Jan 03, 2025 at 04:10:56PM -0600, Bjorn Helgaas wrote:
> Can you make the subject say something about the fix instead of the
> warning?  E.g., something about fixing a potential truncation?
> 
> On Thu, Jan 02, 2025 at 12:13:40PM +0100, Niklas Cassel wrote:
> > Change dw_pcie_edma_irq_verify() to print the dma channel as %u.
> > 
> > While a DWC glue driver could theoretically initialize nr_irqs to a
> > negative value, doing so would obviously be incorrect, and the later
> > dw_edma_probe(struct dw_edma_chip *chip) call would fail, since while
> > the dw_edma_probe() call expects the caller to initialize chip->nr_irqs,
> > dw_edma_probe() verifies nr_irqs and returns failure if nr_irqs is < 1.
> > 
> > This fixes the following build warning when compiling with W=1:
> > 
> > drivers/pci/controller/dwc/pcie-designware.c: In function ‘dw_pcie_edma_detect’:
> > drivers/pci/controller/dwc/pcie-designware.c:989:50: warning: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 3 [-Wformat-truncation=]
> >   989 |                 snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
> >       |                                                  ^~
> > 
> > Signed-off-by: Niklas Cassel <cassel@kernel.org>
> > ---
> > Changes since V1:
> > -Do not reject negative nr_irqs value in dw_pcie_edma_irq_verify(),
> >  as this will already be done by dw_edma_probe().
> > 
> >  drivers/pci/controller/dwc/pcie-designware.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index 3c683b6119c3..0a13fb4336f4 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -986,7 +986,7 @@ static int dw_pcie_edma_irq_verify(struct dw_pcie *pci)
> >  	}
> >  
> >  	for (; pci->edma.nr_irqs < ch_cnt; pci->edma.nr_irqs++) {
> > -		snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
> > +		snprintf(name, sizeof(name), "dma%u", pci->edma.nr_irqs);
> 
> I don't understand this fix.  I guess the warning is complaining that
> sizeof(name) == 6, and "dma" takes up three bytes, so the %d has to
> fit in the remaining region of size 3?

Yes.


> 
> But I don't see how printing nr_irqs as unsigned rather than signed is
> a fix, since even an unsigned int can be longer than 3 digits.

You would need to ask GCC authors behind -Wformat-truncation why the
warning only seems to care about %d.


> 
> And I don't like using "%u" for a signed value in order to "fix"
> something.  That's asking for a future cleanup to revert the change.
>

Well, neither do I. V1 was a nicer solution IMO:
https://lore.kernel.org/linux-pci/20241220072328.351329-2-cassel@kernel.org/
But that fix was rejected by another PCI maintainer.


> What's wrong with just making the name[] buffer big enough?

Sure, I'll do that in v3.


Kind regards,
Niklas

Re: [PATCH v2] PCI: dwc: Fix W=1 build warning in dw_pcie_edma_irq_verify()

[Manivannan Sadhasivam]

On Sat, Jan 04, 2025 at 01:19:48AM +0100, Niklas Cassel wrote:
> On Fri, Jan 03, 2025 at 04:10:56PM -0600, Bjorn Helgaas wrote:
> > Can you make the subject say something about the fix instead of the
> > warning?  E.g., something about fixing a potential truncation?
> > 
> > On Thu, Jan 02, 2025 at 12:13:40PM +0100, Niklas Cassel wrote:
> > > Change dw_pcie_edma_irq_verify() to print the dma channel as %u.
> > > 
> > > While a DWC glue driver could theoretically initialize nr_irqs to a
> > > negative value, doing so would obviously be incorrect, and the later
> > > dw_edma_probe(struct dw_edma_chip *chip) call would fail, since while
> > > the dw_edma_probe() call expects the caller to initialize chip->nr_irqs,
> > > dw_edma_probe() verifies nr_irqs and returns failure if nr_irqs is < 1.
> > > 
> > > This fixes the following build warning when compiling with W=1:
> > > 
> > > drivers/pci/controller/dwc/pcie-designware.c: In function ‘dw_pcie_edma_detect’:
> > > drivers/pci/controller/dwc/pcie-designware.c:989:50: warning: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 3 [-Wformat-truncation=]
> > >   989 |                 snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
> > >       |                                                  ^~
> > > 
> > > Signed-off-by: Niklas Cassel <cassel@kernel.org>
> > > ---
> > > Changes since V1:
> > > -Do not reject negative nr_irqs value in dw_pcie_edma_irq_verify(),
> > >  as this will already be done by dw_edma_probe().
> > > 
> > >  drivers/pci/controller/dwc/pcie-designware.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > index 3c683b6119c3..0a13fb4336f4 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > @@ -986,7 +986,7 @@ static int dw_pcie_edma_irq_verify(struct dw_pcie *pci)
> > >  	}
> > >  
> > >  	for (; pci->edma.nr_irqs < ch_cnt; pci->edma.nr_irqs++) {
> > > -		snprintf(name, sizeof(name), "dma%d", pci->edma.nr_irqs);
> > > +		snprintf(name, sizeof(name), "dma%u", pci->edma.nr_irqs);
> > 
> > I don't understand this fix.  I guess the warning is complaining that
> > sizeof(name) == 6, and "dma" takes up three bytes, so the %d has to
> > fit in the remaining region of size 3?
> 
> Yes.
> 
> 
> > 
> > But I don't see how printing nr_irqs as unsigned rather than signed is
> > a fix, since even an unsigned int can be longer than 3 digits.
> 
> You would need to ask GCC authors behind -Wformat-truncation why the
> warning only seems to care about %d.
> 
> 
> > 
> > And I don't like using "%u" for a signed value in order to "fix"
> > something.  That's asking for a future cleanup to revert the change.
> >
> 
> Well, neither do I. V1 was a nicer solution IMO:
> https://lore.kernel.org/linux-pci/20241220072328.351329-2-cassel@kernel.org/
> But that fix was rejected by another PCI maintainer.
> 

TBH, my concern with v1 was adding negative value check for a signed variable
which doesn't need to be signed. But even so, the fix doesn't fix the underlying
issue but just the GCC warning.

> 
> > What's wrong with just making the name[] buffer big enough?
> 
> Sure, I'll do that in v3.
> 

Yeah, this seems to be the right *fix*.

- Mani

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