> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Segher Boessenkool
> Sent: 2019年2月13日 17:11
> To: Peng Fan <[email protected]>
> Cc: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; Catalin Marinas
> <[email protected]>
> Subject: Re: Warning: unpredictable: identical transfer and status registers
> --`stxr w4,x5,[x4] using aarch64 poky gcc 8.3
>
> OneWed, Feb 13, 2019 at 07:13:21AM +0000, Peng Fan wrote:
> > We met an issue when building a piece jailhouse hypervisor code,
> "stxr %w0, %3, %2\n\t" is
> > compiled as "stxr w4,x5,[x4]" which triggers the warning
> > "Warning: unpredictable: identical transfer and status registers"
>
> This is not a GCC question.
>
> The three registers, in order, are status, transfer, and base. The warning
> claims transfer and status are identical, but in fact base and status are.
> The code (in binutils, gas/config/tc-aarch64.c) is
>
> case ldstexcl:
> /* It is unpredictable if the destination and status registers are the
> same. */
> if ((aarch64_get_operand_class (opnds[0].type)
> == AARCH64_OPND_CLASS_INT_REG)
> && (aarch64_get_operand_class (opnds[1].type)
> == AARCH64_OPND_CLASS_INT_REG)
> && (opnds[0].reg.regno == opnds[1].reg.regno
> || opnds[0].reg.regno == opnds[2].reg.regno))
> as_warn (_("unpredictable: identical transfer and status registers"
> " --`%s'"),
> str);
>
> so either that op0 == op2 test is spurious, or the warning message is
> misleading.
>From aarch64 spec, "stxr w4,x5,[x4]"'s behavior is chip implementation defined,
so I think the warning is correct.
>
> Please ask on [email protected] and/or file a bug at
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsour
> ceware.org%2Fbugzilla%2F&data=02%7C01%7Cpeng.fan%40nxp.com%
> 7C2463376de5aa417d3d6508d69197e4df%7C686ea1d3bc2b4c6fa92cd99c5c
> 301635%7C0%7C0%7C636856478900947075&sdata=pg%2FZmo91Cxfji
> ESlBiR5shmsdxoYWslpfZeAXk5TV30%3D&reserved=0 ?
Ok. I'll post questions to [email protected]
Thanks,
Peng.
>
>
> Segher
>
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