Re: [PATCH][TRIVIAL] Remove bogus "value 0x37ffffff truncated to0x37ffffff" warning.

[Bart Samwel]

Davide Libenzi wrote:
> On Sat, 10 Jan 2004, Bart Samwel wrote:
>
>
> > Tim Cambrant wrote:
> >
> > > On Sat, Jan 10, 2004 at 04:40:30PM +0100, Mario Vanoni wrote:
> > >
> > >
> > > > Compiling the kernel under 2.6.1-mm2, gcc-3.3.2
> > > > (same messages as under 2.6.1-rc1-mm1, re-tested),
> > > >
> > > > arch/i386/boot/setup.S: Assembler messages:
> > > > arch/i386/boot/setup.S:165: Warning: value 0x37ffffff truncated to 
> > > > 0x37ffffff
> > >
> > > This is apparently a known problem and has existed for a long time,
> > > but no-one has fixed it for some reason. I asked the exacly same
> > > question a few months ago, and someone told me that this issue has
> > > been around forever, but is noticed under 2.6, since it is less
> > > verbose during the compilation. I'll pass the message that was told
> > > to me: If you've got a fix, it would surely be included in the kernel.
> >
> > The problem is in the MAXMEM macro. This macro takes the inverse of a 
> > positive number, subtracts another number, and the negative result 
> > overflows the negative range of a 32-bit integer. The assembler 
> > truncates it, but apparently it can't print overly negative numbers 
> > correctly, that's why it looks so strange.
> >
> > My proposed fix is attached: change the macro to subtract the numbers 
> > from 0xFFFFFFFF, and then add 1 at the end. That yields the same result, 
> > but without going through a negative intermediate value that needs to be 
> > truncated.
> >
> > -- Bart
> >
> >
> >
> > --- page.h.orig	2004-01-10 18:15:17.000000000 +0100
> > +++ page.h	2004-01-10 18:15:47.000000000 +0100
> > @@ -123,7 +123,7 @@
> >
> >  #define PAGE_OFFSET		((unsigned long)__PAGE_OFFSET)
> >  #define VMALLOC_RESERVE		((unsigned long)__VMALLOC_RESERVE)
> > -#define MAXMEM			(-__PAGE_OFFSET-__VMALLOC_RESERVE)
> > +#define MAXMEM			(0xFFFFFFFF-__PAGE_OFFSET-__VMALLOC_RESERVE+1)
>
>
> Try:
>
> #define MAXMEM                       (~__PAGE_OFFSET + 1 - __VMALLOC_RESERVE)

I tried that first, before I came up with the solution in the patch, 
because I didn't like the dependency of 0xFFFFFFFF being 32-bit. It was 
a nice idea, but it didn't work. Apparently, gas interprets ~ as a one's 
complement negation operator, not a bitwise or. Therefore, 
~__PAGE_OFFSET is just as negative as -__PAGE_OFFSET as far as gas is 
concerned. It gives me the same warning.

-- Bart
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