Skip to content

L
linux-davinci
Switch branch/tag
  1. 18 Jan, 2007 8 commits
    • Nicolas Pitre's avatar
      [ARM] 4016/1: prefetch macro is wrong wrt gcc's "delete-null-pointer-checks" · 563c5768
      Nicolas Pitre authored 
       optimization

The gcc manual says:

|`-fdelete-null-pointer-checks'
|     Use global dataflow analysis to identify and eliminate useless
|     checks for null pointers.  The compiler assumes that dereferencing
|     a null pointer would have halted the program.  If a pointer is
|     checked after it has already been dereferenced, it cannot be null.
|     Enabled at levels `-O2', `-O3', `-Os'.

Now the problem can be seen with this test case:

#include <linux/prefetch.h>
extern void bar(char *x);
void foo(char *x)
{
	prefetch(x);
	if (x)
		bar(x);
}

Because the constraint to the inline asm used in the prefetch() macro is
a memory operand, gcc assumes that the asm code does dereference the
pointer and the delete-null-pointer-checks optimization kicks in.
Inspection of generated assembly for the above example shows that bar()
is indeed called unconditionally without any test on the value of x.

Of course in the prefetch case there is no real dereference and it
cannot be assumed that a null pointer would have been caught at that
point. This causes kernel oopses with constructs like
hlist_for_each_entry() where the list's 'next' content is prefetched
before the pointer is tested against NULL, and only when gcc feels like
applying this optimization which doesn't happen all the time with more
complex code.

It appears that the way to prevent delete-null-pointer-checks
optimization to occur in this case is to make prefetch() into a static
inline function instead of a macro. At least this is what is done on
x86_64 where a similar inline asm memory operand is used (I presume they
would have seen the same problem if it didn't work) and resulting code
for the above example confirms that.

An alternative would consist of replacing the memory operand by a
register operand containing the pointer, and use the addressing mode
explicitly in the asm template. But that would be less optimal than an
offsettable memory reference.
Signed-off-by: default avatarNicolas Pitre <nico@cam.org>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      563c5768
    • Russell King's avatar
      [ARM] Add sys_*at syscalls · 0cb96821
      Russell King authored 
      Later glibc requires the *at syscalls.  Add them.
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      0cb96821
    • Russell King's avatar
      [ARM] Formalise the ARMv6 processor name string · 5702ed03
      Russell King authored 
      Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      5702ed03
    • Russell King's avatar
      [ARM] Handle HWCAP_VFP in VFP support code · 854de764
      Russell King authored 
      Don't set HWCAP_VFP in the processor support file; not only does it
depend on the processor features, but it also depends on the support
code being present.  Therefore, only set it if the support code
detects that we have a VFP coprocessor attached.

Also, move the VFP handling of the coprocessor access register into
the VFP support code.
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      854de764
    • Russell King's avatar
      [ARM] Fix Versatile PB initialisation to use .init_machine · e3b8b8e1
      Russell King authored 
      There's no point having the Versatile PB initialisation using an
arch_initcall() and then checking whether it's running on a
Versatile PB board - this is what the .init_machine function
pointer in the machine description is for.  Use it.
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      e3b8b8e1
    • Paul Gortmaker's avatar
      [ARM] 3911/2: Simplify alloc_thread_info on ARM · 9f661896
      Paul Gortmaker authored 
      Remove ARM local cache of 4 struct thread_info.
Can cause oops under certain circumstances.

Russell indicated the original optimization was
required on older kernels to avoid thread starvation
on memory fragmentation, but may no longer be
required.  I've updated the patch to 19rc4 and
ensured no <config.h> dain-bramage slipped in this
time (sorry about that).

Original description follows:

I was given some test results which pointed to an
Oops in alloc_thread_info (happened 2x), and after
looking at the code, I see that ARM has its own
local cache of 4 struct thread_info. There wasn't
any clear (to me) synchronization between the
alloc_thread_info and the free_thread_info.

I looked over the other arch, and they all simply
allocate them on an as needed basis, so I simplified
the ARM to do the same, based on the other arch
(e.g. PPC) and the folks doing the testing have
indicated that this fixed the oops.
Signed-off-by: default avatarPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      9f661896
    • Russell King's avatar
      [ARM] Move HWCAP_* definitions to asm/elf.h · ced6b4c0
      Russell King authored 
      Move HWCAP_* definitions into asm/elf.h, where they should belong.
Since userspace wants to get at these definitions by including
asm/procinfo.h, include asm/elf.h from this file if __KERNEL__
is not defined, and issue a warning suggesting to fix the program
up to use asm/elf.h instead.
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      ced6b4c0
    • Russell King's avatar
      [ARM] Include asm/elf.h instead of asm/procinfo.h · e83087d9
      Russell King authored 
      These files want to provide/access ELF hwcap information, so should
be including asm/elf.h rather than asm/procinfo.h
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      e83087d9
  3. 17 Jan, 2007 1 commit
  5. 29 Nov, 2006 22 commits
  7. 28 Nov, 2006 9 commits