Re: [Qemu-devel] [PATCH v3 10/11] tcg-mips: Adjust qemu_ld/st for mips64

["Jin Guojie" <jinguojie@loongson.cn>]

In Richard's v2 patch (shown as below), the compilation on mips64 host is disabled.

-#define LO_OFF    (MIPS_BE * 4)
-#define HI_OFF    (4 - LO_OFF)
+#if TCG_TARGET_REG_BITS == 32
+# define LO_OFF  (MIPS_BE * 4)
+# define HI_OFF  (4 - LO_OFF)
+#else
+extern int link_error(void);
+# define LO_OFF  link_error()
+# define HI_OFF  link_error()
+#endif

When I compiled this patch on Loongson as mips64el, a link error occured:

  LINK    i386-softmmu/qemu-system-i386
tcg/tcg.o: In function `tcg_out_tlb_load':
tcg-target.inc.c:1252: undefined reference to `link_error'

To pass the compilation, I removed the link_error() and redefined LO_OFF/HI_OFF. 
It works OK on little-endian mips o32/n64 host. I have no big-endian mips machine,
so the bug on big-endian is not discovered.

Frankly speaking, I didn't take n32 into consideration until you pointed out that.
I feel that n32 is rarely used in current and future market. I can not even find an n32 
debian distribution in Aurelien's qemu image collection.
How about leave n32 as a TODO feature?

Jin Guojie

------------------ Original ------------------
From:  "Richard Henderson";<rth@twiddle.net>;
Date:  Nov 25, 2016
To:  "Jin Guojie"<jinguojie@loongson.cn>; "qemu-devel"<qemu-devel@nongnu.org>; 
Cc:  "Aurelien Jarno"<aurelien@aurel32.net>; "James Hogan"<james.hogan@imgtec.com>; 
Subject:  Re: [PATCH v3 10/11] tcg-mips: Adjust qemu_ld/st for mips64



On 11/25/2016 04:31 AM, Jin Guojie wrote:
> -#define LO_OFF    (MIPS_BE * 4)
> -#define HI_OFF    (4 - LO_OFF)
> +# define LO_OFF  (MIPS_BE * sizeof(long))
> +# define HI_OFF  (sizeof(long) - LO_OFF)

For n32, sizeof(long) == 4, and for n64, sizeof(long) == 8.  So in the end this 
change must be wrong for big-endian.

Surely using link_error, as my patch did, to assert at compile-time that these 
values were never used for TCG_TARGET_REGS == 64 is better.


r~