Re: [PATCH 14/22] parisc: %pF is only for function pointers

[John David Anglin]

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@xxxxxxxx

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