linux-kernel - Re: [RFC] arm64:use set_fixmap

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Date:	Fri, 24 Jul 2015 11:07:24 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	yalin wang <yalin.wang2010@...il.com>
Cc:	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Punit Agrawal <Punit.Agrawal@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"zlim.lnx@...il.com" <zlim.lnx@...il.com>,
	"wcohen@...hat.com" <wcohen@...hat.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC] arm64:use set_fixmap_offset to make it more clear

On Fri, Jul 24, 2015 at 10:56:18AM +0100, Mark Rutland wrote:
> On Fri, Jul 24, 2015 at 04:56:59AM +0100, yalin wang wrote:
> > 
> > > On Jul 23, 2015, at 21:03, Catalin Marinas <catalin.marinas@....com> wrote:
> > > 
> > > On Thu, Jul 23, 2015 at 07:45:53PM +0800, yalin wang wrote:
> > >> A little change to patch_map() function,
> > >> use set_fixmap_offset() to make code more clear.
> > >> 
> > >> Signed-off-by: yalin wang <yalin.wang2010@...il.com>
> > >> ---
> > >> arch/arm64/kernel/insn.c | 5 ++---
> > >> 1 file changed, 2 insertions(+), 3 deletions(-)
> > >> 
> > >> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
> > >> index dd9671c..7dafd5a 100644
> > >> --- a/arch/arm64/kernel/insn.c
> > >> +++ b/arch/arm64/kernel/insn.c
> > >> @@ -101,9 +101,8 @@ static void __kprobes *patch_map(void *addr, int fixmap)
> > >> 		return addr;
> > >> 
> > >> 	BUG_ON(!page);
> > >> -	set_fixmap(fixmap, page_to_phys(page));
> > >> -
> > >> -	return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
> > >> +	return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
> > >> +			(addr & ~PAGE_MASK));
> > > 
> > > It looks fine. Do you get any compiler warning for the automatic pointer
> > > to long conversion? You may want to add some explicit casts, otherwise:
> > > 
> > > Acked-by: Catalin Marinas <catalin.marinas@....com>
> > i have build it, there is no warning about this change. :)
> 
> I see no warnings with defconfig, but there's an (unrelated) set of warnings if
> CONFIG_DEBUG_SET_MODULE_RONX or CONFIG_DEBUG_RODATA are enabled:

Actually they aren't unrelated after all. the unsigned long addr in
__set_fixmap_offset shadows the void* addr from patch_map making the
types match.

With a few underscores addrd to __set_fixmap_offset's addr, I get the
following regarding patch_map:

----
In file included from ./arch/arm64/include/asm/fixmap.h:85:0,
                 from arch/arm64/kernel/insn.c:32:
arch/arm64/kernel/insn.c: In function ‘patch_map’:
arch/arm64/kernel/insn.c:105:10: error: invalid operands to binary & (have ‘void *’ and ‘long unsigned int’)
    (addr & ~PAGE_MASK));
          ^
include/asm-generic/fixmap.h:73:20: note: in definition of macro ‘__set_fixmap_offset’
  __set_fixmap(idx, phys, flags);         \
                    ^
arch/arm64/kernel/insn.c:104:17: note: in expansion of macro ‘set_fixmap_offset’
  return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
                 ^
arch/arm64/kernel/insn.c:105:10: error: invalid operands to binary & (have ‘void *’ and ‘long unsigned int’)
    (addr & ~PAGE_MASK));
          ^
include/asm-generic/fixmap.h:74:32: note: in definition of macro ‘__set_fixmap_offset’
  __addr = fix_to_virt(idx) + ((phys) & (PAGE_SIZE - 1)); \
                                ^
arch/arm64/kernel/insn.c:104:17: note: in expansion of macro ‘set_fixmap_offset’
  return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
                 ^
make[1]: *** [arch/arm64/kernel/insn.o] Error 1
make: *** [arch/arm64/kernel/insn.o] Error 2
----

we need both the cast in patch_map, and an update to __set_fixmap_offset to
prevent the name clash.

Thanks,
Mark.
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