lkml.org 
[lkml]   [2018]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] ARM: copypage-fa: add kto and kfrom to input operands list
On Tue, Oct 16, 2018 at 12:39:54AM +0200, Stefan Agner wrote:
> On 16.10.2018 00:23, Russell King - ARM Linux wrote:
> > On Tue, Oct 16, 2018 at 12:16:29AM +0200, Stefan Agner wrote:
> >> When functions incoming parameters are not in input operands list gcc
> >> 4.5 does not load the parameters into registers before calling this
> >> function but the inline assembly assumes valid addresses inside this
> >> function. This breaks the code because r0 and r1 are invalid when
> >> execution enters v4wb_copy_user_page ()
> >
> > NAK. Naked functions must never be inlined. Please add a "noinline"
> > attribute to the function rather than making things more complex.
> >
>
> To be honest, I did not put much thought into this commit since it is
> just doing to copypage-fa.c what 9a40ac86152c ("ARM: 6164/1: Add kto and
> kfrom to input operands list.") has been done to the other copypage
> implementations...
>
> [adding Khem]
>
> > The GCC manual states:
> >
> > `naked'
> > Use this attribute on the ARM, AVR, MCORE, MSP430, NDS32, RL78, RX
> > and SPU ports to indicate that the specified function does not
> > need prologue/epilogue sequences generated by the compiler. It is
> > up to the programmer to provide these sequences. The only
> > ^^^^^^^^
> > statements that can be safely included in naked functions are
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > `asm' statements that do not have operands. All other statements,
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > including declarations of local variables, `if' statements, and so
> > forth, should be avoided. Naked functions should be used to
> > implement the body of an assembly function, while allowing the
> > compiler to construct the requisite function declaration for the
> > assembler.
> >
> > The 'I' attribute is fine here because it is a constant that is not
> > allowed to be in a register (and hence has no code generation side
> > effects.)
> >
> > Adding operands for the input parameters, however, isn't going to
> > work around the fact that _this_ assembly is written to be out of
> > line and so it must never be inlined by the compiler.
>
> I briefly looked at a disassembled version after applying both patches,
> it indeed leads to inlining. However, the code seems to be working
> (thanks to asm volatile?)...

Apart from v4wb_copy_user_page() and mc_copy_user_page(), how is
Clang inlining these static functions that are only used through
function pointers?

--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up

\
 
 \ /
  Last update: 2018-10-16 00:47    [W:0.048 / U:1.320 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site