Arm64: assembling adrp with operand involving .
Jan Beulich
jbeulich@suse.com
Mon Feb 14 14:04:51 GMT 2022
On 14.02.2022 14:35, Nick Clifton wrote:
>> I would expect these two
>>
>> adrp x0, .
>> 1: adrp x0, 1b
>>
>> to assemble to the same encoding with similar attached relocations.
>
> Me too.
>
>> The first, however, appears to have evaluation of . deferred until the
>> end of assembly, i.e. the resulting operand depends on the number of
>> subsequent insns in the same source file. At a guess this is fallout
>> from eac4eb8ecb26 "Fix a problem assembling AArch64 sources when a
>> relocation is generated against a..." (for some reason the title is
>> truncated).
>
> That is because I put the rest of the description on a second line, sorry.
> The second line reads:
>
> generated against a symbol that has a defined value.
>
> The patch was created as a fix for PR 27217.
>
>> According to my observations other insns aren't affected,
>> yet the change to parse_adrp() doesn't really stand out in said commit.
>> Hence I'm neither really certain that's the one, nor how a possible fix
>> could look like. Do you have any thoughts?
>
> Well the change added a new argument to the ...get_expression() function,
> so all callers were updated. There was no specific intention to change
> parse_adrp for some other reason.
>
> Anyway - this does look like a bug, although I think that it might be
> restricted to just an unadorned reference to dot. ie:
>
> adrp x0, .
> 1: adrp x0, 1b
> adrp x0, . - 8
>
> When assembled and then dumped, gives:
>
> 0000000000000000 <.text>:
> 0: 90000000 adrp x0, 0 <.text>
> 0: R_AARCH64_ADR_PREL_PG_HI21 .text+0xc
> 4: 90000000 adrp x0, 0 <.text>
> 4: R_AARCH64_ADR_PREL_PG_HI21 .text+0x4
> 8: 90000000 adrp x0, 0 <.text>
> 8: R_AARCH64_ADR_PREL_PG_HI21 .text+0x4
>
> So the ". - 8" expression has evaluated correctly, but the "." expression
> has not.
I've mentioned this aspect in the bug (see below), but now that I look
again I'm not sure anymore: Wouldn't this be .text+0? And isn't it
getting close only because no further insns are following?
> Would you care to open a BZ for this ?
Bug 28888.
Jan
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