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Sender: Richard Henderson <rth7680@gmail.com>
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From: Richard Henderson <rth@twiddle.net>
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Subject: Re: [Qemu-devel] [PATCH] tci: Detect function argument alignment
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To: Stefan Weil <sw@weilnetz.de>
Cc: Peter Maydell <peter.maydell@linaro.org>, qemu-devel <qemu-devel@nongnu.org>

On 09/12/2013 01:40 PM, Stefan Weil wrote:
> Am 12.09.2013 22:29, schrieb Richard Henderson:
>> On 09/12/2013 12:45 PM, Stefan Weil wrote:
>>> +cat > $TMPC << EOF
>>> +#include <stdbool.h>
>>> +#include <stdio.h>
>>> +#include <stdint.h>
>>> +#include <inttypes.h>
>>> +static bool call_align_args(uint32_t arg1, uint64_t arg2) {
>>> +  if (arg2 == 0x000000030000004ULL || arg2 == 0x0000000400000003ULL) {
>>> +    return true;
>>> +  } else if (arg2 == 2) {
>>> +    /* 64 bit host, 64 bit function arguments are not aligned. */
>>> +  } else if (arg2 == 0x0000000200000003 || arg2 == 0x0000000300000002ULL) {
>>> +    /* 64 bit function arguments are not aligned. */
>>> +  } else {
>>> +    fprintf(stderr, "unexpected 64 bit function argument 0x%016" PRIx64 "\n", arg2);
>>> +  }
>>> +  return false;
>>> +}
>> You will of course be printing that error when run on a 64-bit host.
> 
> No. See the comment in the code where a 64 bit host is handled.

Oh, I see that now, sorry.

>> Or perhaps skip that detection and define it always.  It's more likely
>> to be right than not doing it.  This will break if MIPS64 were added,
>> but then we'd have to extend tcg_gen_callN for that anyway.
> 
> Would this break x86_64 hosts? They don't define it as far as I could see.

Any 64-bit host that doesn't define TCG_TARGET_EXTEND_ARGS has an
abi that considers the high bits of a 32-bit parameter to be garbage.

Thus extending the value on x86_64 host is unused work, but certainly
not harmful.


r~