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    SubjectRe: [PATCH 14/22] parisc: %pF is only for function pointers
    On 2015-03-12 8:11 AM, James Bottomley wrote:
    > On Wed, 2015-03-11 at 22:13 -0500, Scott Wood wrote:
    >> Use %pS for actual addresses, otherwise you'll get bad output
    >> on arches like ppc64 where %pF expects a function descriptor. Even on
    >> other architectures, refrain from setting a bad example that people
    >> copy.
    > Are you sure about this? Parisc64 is a function description
    > architecture. There may be a misunderstanding about what
    > __builtin_return_address(0) is supposed to return, but I'm certain the
    > person who added the code thought it returned a function pointer, which
    > on parisc64 would be a descriptor.

    __builtin_return_address(0) returns the return address in the calling procedure
    ignoring import/export stubs. There are no function descriptors for return addresses.
    Thus, it can't return a function pointer.

    There are no function descriptors in 32-bit parisc when the -mfast-indirect-calls
    compiler option is used.

    This option used to be used for 64-bit kernel builds but this broke when the
    -mfast-indirect-calls was fixed for user space (gcl uses it). I worked a bit
    on trying to eliminate function descriptors from the 64-bit kernel for performance
    but I don't have a working change.

    Dave

    --
    John David Anglin dave.anglin@bell.net



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