linux-kernel - Re: [PATCH] sh: pgtable-3level: Fix cast to pointer from integer of different size

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Date:   Fri, 17 Sep 2021 11:21:09 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rob Landley <rob@...dley.net>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Daniel Palmer <daniel@...f.com>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sh: pgtable-3level: Fix cast to pointer from integer of
 different size

Hi Rob,

On Fri, Sep 17, 2021 at 3:12 AM Rob Landley <rob@...dley.net> wrote:
> On 9/15/21 8:50 AM, Geert Uytterhoeven wrote:
> >     arch/sh/include/asm/pgtable-3level.h:37:9: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> ...
> > The truncation to "unsigned long" has been there since forever, so
> > probably it still works fine ;-)
>
> 1) Linux is LP64 so sizeof(long) and sizeof(pointer) always match, so it's not
> truncating.
>
> 2) The sh5 only ever shipped evaluation units, it never had a production run,
> and we haven't implemented j64 yet, so all superh targets are currently 32 bit.
> (I.E. it's complaining about _expanding_ the pointer, which shouldn't be a
> problem as long as endianness is respected.)

The build error is for 32-bit.
If CONFIG_X2TLB=y, pgd_t.pgd is "unsigned long long", i.e. 64-bit, so
casting it to a pointer needs an intermediate cast to "unsigned long".
See arch/sh/include/asm/page.h:

#ifdef CONFIG_X2TLB
typedef struct { unsigned long pte_low, pte_high; } pte_t;
typedef struct { unsigned long long pgprot; } pgprot_t;
typedef struct { unsigned long long pgd; } pgd_t;
#define pte_val(x) \
        ((x).pte_low | ((unsigned long long)(x).pte_high << 32))
#define __pte(x) \
        ({ pte_t __pte = {(x), ((unsigned long long)(x)) >> 32}; __pte; })
#else
typedef struct { unsigned long pte_low; } pte_t;
typedef struct { unsigned long pgprot; } pgprot_t;
typedef struct { unsigned long pgd; } pgd_t;
#define pte_val(x)      ((x).pte_low)
#define __pte(x)        ((pte_t) { (x) } )
#endif

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds