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@xxxxxxxxxx>
> > > ---
> > > 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@xxxxxxxxxx/
> 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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