On Thu, Apr 4, 2013 at 12:01 PM, Gabor Juhos <juhosg@xxxxxxxxxxx> wrote:
> Due to the __weak annotation in the forward declaration
> of the 'pcibios_get_phb_of_node' function GCC will emit
> a weak symbol for this functions even if the actual
> implementation does not use the weak attribute.
>
> If an architecture tries to override the function
> by providing its own implementation there will be
> multiple weak symbols with the same name in the
> object files. When the kernel is linked from the
> object files the linking order determines which
> implementation will be used in the final image.
>
> On x86 and on powerpc the architecture specific
> version gets used:
>
> $ readelf -s arch/x86/kernel/built-in.o drivers/pci/built-in.o \
> vmlinux.o | grep pcibios_get_phb_of_node
> 3338: 00029b80 86 FUNC WEAK DEFAULT 1 pcibios_get_phb_of_node
> 1701: 00012710 77 FUNC WEAK DEFAULT 1 pcibios_get_phb_of_node
> 52072: 0002a170 86 FUNC WEAK DEFAULT 1 pcibios_get_phb_of_node
> $
>
> $ powerpc-openwrt-linux-uclibc-readelf -s arch/powerpc/kernel/built-in.o \
> drivers/pci/built-in.o vmlinux.o | grep pcibios_get_phb_of_node
> 1001: 0000cbb8 12 FUNC WEAK DEFAULT 1 pcibios_get_phb_of_node
> 1484: 0001471c 88 FUNC WEAK DEFAULT 1 pcibios_get_phb_of_node
> 28652: 0000d6f8 12 FUNC WEAK DEFAULT 1 pcibios_get_phb_of_node
> $
>
> However on MIPS, the linker puts the default
> implementation into the final image:
>
> $ mipsel-openwrt-linux-readelf -s arch/mips/pci/built-in.o \
> drivers/pci/built-in.o vmlinux.o | grep pcibios_get_phb_of_node
> 86: 0000046c 12 FUNC WEAK DEFAULT 2 pcibios_get_phb_of_node
> 1430: 00012e2c 104 FUNC WEAK DEFAULT 2 pcibios_get_phb_of_node
> 31898: 0017e4ec 104 FUNC WEAK DEFAULT 2 pcibios_get_phb_of_node
> $
>
> Rename the default implementation and remove the
> __weak annotation of that. This ensures that there
> will be no multiple weak symbols with the same name
> in the object files. In order to keep the expected
> behaviour, call the architecture specific function
> if the weak symbol is resolved.
>
> Also move the renamed function to the top instead
> of adding a new forward declaration for that.
>
> Signed-off-by: Gabor Juhos <juhosg@xxxxxxxxxxx>
> ---
> Notes:
>
> Unfortunately I'm not a binutils/gcc expert, so
> I don't know if this is the expected behaviour
> of those or not.
>
> Removing the __weak annotation from the forward
> declaration of 'pcibios_get_phb_of_node' in
> 'include/linux/pci.h' also fixes the problem.
>
> The microblaze architecture also provides its own
> implementation. The behaviour of that is not tested
> but I assume that the linker chooses the arch specific
> implementation on that as well similarly to the
> x86/powerpc.
>
> The MIPS version is implemented in the followup
> patch.
>
> Removing the __weak annotation from the forward
> declaration of 'pcibios_get_phb_of_node' in
> 'include/linux/pci.h' also fixes the problem.
I think removing the __weak annotation from the declaration in
include/linux/pci.h is the correct solution.
__weak is an attribute of a function definition, not an attribute of
the interface, so I don't think it makes any sense to have it in
pci.h.
Bjorn
> -Gabor
> ---
> drivers/pci/of.c | 41 +++++++++++++++++++++++------------------
> 1 file changed, 23 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index f092993..5794840 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -15,10 +15,32 @@
> #include <linux/of_pci.h>
> #include "pci.h"
>
> +static struct device_node *__pcibios_get_phb_of_node(struct pci_bus *bus)
> +{
> + /* This should only be called for PHBs */
> + if (WARN_ON(bus->self || bus->parent))
> + return NULL;
> +
> + if (pcibios_get_phb_of_node)
> + return pcibios_get_phb_of_node(bus);
> +
> + /* Look for a node pointer in either the intermediary device we
> + * create above the root bus or it's own parent. Normally only
> + * the later is populated.
> + */
> + if (bus->bridge->of_node)
> + return of_node_get(bus->bridge->of_node);
> + if (bus->bridge->parent && bus->bridge->parent->of_node)
> + return of_node_get(bus->bridge->parent->of_node);
> +
> + return NULL;
> +}
> +
> void pci_set_of_node(struct pci_dev *dev)
> {
> if (!dev->bus->dev.of_node)
> return;
> +
> dev->dev.of_node = of_pci_find_child_device(dev->bus->dev.of_node,
> dev->devfn);
> }
> @@ -32,7 +54,7 @@ void pci_release_of_node(struct pci_dev *dev)
> void pci_set_bus_of_node(struct pci_bus *bus)
> {
> if (bus->self == NULL)
> - bus->dev.of_node = pcibios_get_phb_of_node(bus);
> + bus->dev.of_node = __pcibios_get_phb_of_node(bus);
> else
> bus->dev.of_node = of_node_get(bus->self->dev.of_node);
> }
> @@ -42,20 +64,3 @@ void pci_release_bus_of_node(struct pci_bus *bus)
> of_node_put(bus->dev.of_node);
> bus->dev.of_node = NULL;
> }
> -
> -struct device_node * __weak pcibios_get_phb_of_node(struct pci_bus *bus)
> -{
> - /* This should only be called for PHBs */
> - if (WARN_ON(bus->self || bus->parent))
> - return NULL;
> -
> - /* Look for a node pointer in either the intermediary device we
> - * create above the root bus or it's own parent. Normally only
> - * the later is populated.
> - */
> - if (bus->bridge->of_node)
> - return of_node_get(bus->bridge->of_node);
> - if (bus->bridge->parent && bus->bridge->parent->of_node)
> - return of_node_get(bus->bridge->parent->of_node);
> - return NULL;
> -}
> --
> 1.7.10
>
