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

[Bjorn Helgaas <helgaas@kernel.org>]

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
>