[x265] PING [PATCH] aarch64: replace ldr pseudo-instruction with adrp+add

[Fangrui Song]

On Thu, Oct 6, 2022 at 1:39 AM chen <chenm003 at 163.com> wrote:

> Hi Song,
>
>
> I means the current tree support these adrp+add mode with compile option
> -DPIC, so we need not patch the code.
>
>
> Regards,
> Min Chen
>

Hi Min, IIUC -DPIC is only defined for x86-64
(source/cmake/CMakeASM_NASMInformation.cmake).
AArch64 does not get -DPIC.

> 2022-10-06 06:42:33，"Fangrui Song" <maskray at google.com>
>
> Hi Min, sorry but I just saw your question. I do not understand the
> request.
> adrp+add is just strictly superior to ldr (which uses a constant pool and
> does not decrease code size) and avoids text relocations (which are
> prohibited in many systems).  `ldr             \rd, =\val+\offset` should
> just be removed. adrp+add also works on Mach-O systems as well.
>
>
>> At 2022-09-24 15:21:35, "Fangrui Song" <maskray at google.com> wrote:
>> >Ping.  The breaks lld build and some binutils configurating defaulting
>> >to disallow text relocations.
>> >
>> >On 2022-08-29, Fangrui Song wrote:
>> >>On 2022-08-29, Fangrui Song wrote:
>> >>>On 2022-08-30, chen wrote:
>> >>>>Hi Song,
>> >>>>
>> >>>>
>> >>>>Thank you for your patch.
>> >>>>
>> >>>>
>> >>>>However, syntax of ':lo12:' depends on compiler, so more general LDR is better in here.
>> >>>>
>> >>>>
>> >>>>Regards,
>> >>>>Min Chen
>> >>>
>> >>>:lo12: is standard aarch64 assembly syntax.
>> >>>Which aarch64 compiler supported by x265 does not support :lo12:?
>> >>
>> >>Note that LDR has another problem that it produced an absolute relocation R_AARCH64_ABS64. It will trigger an error
>> >>when text relocations are disabled (default in ld.lld. See https://maskray.me/blog/2020-12-19-lld-and-gnu-linker-incompatibilities#:~:text=Text%20relocations)
>> >>
>> >>```
>> >>% : && /usr/bin/c++ -fPIC -O3 -DNDEBUG  -Wl,-Bsymbolic,-znoexecstack -shared ...
>> >>ld: error: relocation R_AARCH64_ABS64 cannot be used against local
>> >>symbol; recompile with -fPIC
>> >>>>>defined in sad-a.S.o
>> >>>>>>>> referenced by sad-a.S.o:(.text+0x9B00)
>> >>```
>> >>
>> >>adrp+add work fine.
>> >>
>> >>(I am a maintainer of lld/ELF.)
>> >>
>> >>>>At 2022-08-30 02:33:37, "Fangrui Song" <maskray at google.com> wrote:
>> >>>>>The ldr pseudo-instruction uses a literal pool, which is less efficient
>> >>>>>and does not decrease the code size.
>> >>>>>---
>> >>>>>source/common/aarch64/asm.S | 4 +---
>> >>>>>1 file changed, 1 insertion(+), 3 deletions(-)
>> >>>>>
>> >>>>>diff --git a/source/common/aarch64/asm.S b/source/common/aarch64/asm.S
>> >>>>>index 399c37cf2..2506f50aa 100644
>> >>>>>--- a/source/common/aarch64/asm.S
>> >>>>>+++ b/source/common/aarch64/asm.S
>> >>>>>@@ -130,11 +130,9 @@ ELF     .size   \name, . - \name
>> >>>>>       adrp            \rd, \val+(\offset)
>> >>>>>       add             \rd, \rd, :lo12:\val+(\offset)
>> >>>>> .endif
>> >>>>>-#elif defined(PIC)
>> >>>>>+#else
>> >>>>>       adrp            \rd, \val+(\offset)
>> >>>>>       add             \rd, \rd, :lo12:\val+(\offset)
>> >>>>>-#else
>> >>>>>-        ldr             \rd, =\val+\offset
>> >>>>>#endif
>> >>>>>.endm
>> >>>>>
>> >>>>>--
>> >>>>>2.37.2.672.g94769d06f0-goog
>> >>>>>
>> >>>>>_______________________________________________
>> >>>>>x265-devel mailing list
>> >>>>>x265-devel at videolan.org
>> >>>>>https://mailman.videolan.org/listinfo/x265-devel
>> >>>
>> >>>>_______________________________________________
>> >>>>x265-devel mailing list
>> >>>>x265-devel at videolan.org
>> >>>>https://mailman.videolan.org/listinfo/x265-devel
>> >>>
>> >_______________________________________________
>> >x265-devel mailing list
>> >x265-devel at videolan.org
>> >https://mailman.videolan.org/listinfo/x265-devel
>>
>> _______________________________________________
>> x265-devel mailing list
>> x265-devel at videolan.org
>> https://mailman.videolan.org/listinfo/x265-devel
>>
>
>
> --
> 宋方睿
>
> _______________________________________________
> x265-devel mailing list
> x265-devel at videolan.org
> https://mailman.videolan.org/listinfo/x265-devel
>


-- 
宋方睿
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.videolan.org/pipermail/x265-devel/attachments/20221017/a72279d2/attachment.html>