Re: [PATCH 11/22] pci: lto: fix PREL32 relocations

Bjorn Helgaas
2020-07-17T20:26:26Z

OK by me, but please update the subject to match convention:

PCI: Fix PREL32 relocations for LTO

and include a hint in the commit log about what LTO is. At least
expand the initialism once. Googling for "LTO" isn't very useful.

With Clang's Link Time Optimization (LTO), the compiler ... ?

On Wed, Jun 24, 2020 at 01:31:49PM -0700, Sami Tolvanen wrote:
> With LTO, the compiler can rename static functions to avoid global
> naming collisions. As PCI fixup functions are typically static,
> renaming can break references to them in inline assembly. This
> change adds a global stub to DECLARE_PCI_FIXUP_SECTION to fix the
> issue when PREL32 relocations are used.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
> include/linux/pci.h | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index c79d83304e52..1e65e16f165a 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1909,19 +1909,24 @@ enum pci_fixup_pass {
> };
>
> #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
> -#define __DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class, \
> - class_shift, hook) \
> - __ADDRESSABLE(hook) \
> +#define ___DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class, \
> + class_shift, hook, stub) \
> + void stub(struct pci_dev *dev) { hook(dev); } \
> asm(".section " #sec ", \"a\" \n" \
> ".balign 16 \n" \
> ".short " #vendor ", " #device " \n" \
> ".long " #class ", " #class_shift " \n" \
> - ".long " #hook " - . \n" \
> + ".long " #stub " - . \n" \
> ".previous \n");
> +
> +#define __DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class, \
> + class_shift, hook, stub) \
> + ___DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class, \
> + class_shift, hook, stub)
> #define DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class, \
> class_shift, hook) \
> __DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class, \
> - class_shift, hook)
> + class_shift, hook, __UNIQUE_ID(hook))
> #else
> /* Anonymous variables would be nice... */
> #define DECLARE_PCI_FIXUP_SECTION(section, name, vendor, device, class, \
> --
> 2.27.0.212.ge8ba1cc988-goog
>