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From: "Gao, Liming" <liming.gao@intel.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	edk2-devel-01 <edk2-devel@lists.01.org>,
	"Zhu, Yonghong" <yonghong.zhu@intel.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>,
	"Cohen, Eugene" <eugene@hp.com>
Subject: Re: [PATCH 1/2] BaseTools/GenFw AARCH64: convert ADRP to ADR if binary size allows it
Date: Mon, 1 Aug 2016 14:09:54 +0000	[thread overview]
Message-ID: <4A89E2EF3DFEDB4C8BFDE51014F606A1155E30C4@shsmsx102.ccr.corp.intel.com> (raw)
In-Reply-To: <CAKv+Gu_fsdDeE5ueJoS80r9gxwAueufyO34DKi+ejJEpnJ5wvw@mail.gmail.com>

Ard:
  Your change is OK to me. I have no comment.

Thanks
Liming
From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
Sent: Monday, August 1, 2016 7:53 PM
To: edk2-devel-01 <edk2-devel@lists.01.org>; Gao, Liming <liming.gao@intel.com>; Zhu, Yonghong <yonghong.zhu@intel.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>; Cohen, Eugene <eugene@hp.com>; Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: [PATCH 1/2] BaseTools/GenFw AARCH64: convert ADRP to ADR if binary size allows it

On 27 July 2016 at 13:26, Ard Biesheuvel wrote:
> The ADRP instruction in the AArch64 ISA requires the link time and load
> time offsets of a binary to be equal modulo 4 KB. The reason is that this
> instruction always produces a multiple of 4 KB, and relies on a subsequent
> ADD or LDR instruction to set the offset into the page. The resulting
> symbol reference only produces the correct value if the symbol in question
> resides at that exact offset into the page, and so loading the binary at
> arbitrary offsets is not possible.
>
> Due to the various levels of padding when packing FVs into FVs into FDs,
> this alignment is very costly for XIP code, and so we would like to relax
> this alignment requirement if possible.
>
> Given that symbols that are sufficiently close (within 1 MB) of the
> reference can also be reached using an ADR instruction which does not
> suffer from this alignment issue, let's replace ADRP instructions with ADR
> after linking if the offset can be encoded in this instruction's immediate
> field. Note that this only makes sense if the section alignment is < 4 KB.
> Otherwise, replacing the ADRP has no benefit, considering that the
> subsequent ADD or LDR instruction is retained, and that micro-architectures
> are more likely to be optimized for ADRP/ADD pairs (i.e., via micro op
> fusing) than for ADR/ADD pairs, which are non-typical.
>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel

@Liming, @Leif:

are there any objections to these patches? I know it is unfortunate
that we need to modify instructions as part of the ELF to PE/COFF
conversion, but it is very effective

ArmVirtQemu-AARCH64 built with CLANG35:

Before:

FVMAIN_COMPACT [41%Full] 2093056 total, 868416 used, 1224640 free
FVMAIN [99%Full] 4848064 total, 4848008 used, 56 free

After:

FVMAIN_COMPACT [36%Full] 2093056 total, 768064 used, 1324992 free
FVMAIN [99%Full] 4848064 total, 4848008 used, 56 free

For comparision, GCC49

FVMAIN_COMPACT [35%Full] 2093056 total, 749960 used, 1343096 free
FVMAIN [99%Full] 3929088 total, 3929032 used, 56 free

and GCC5 (with LTO)

FVMAIN_COMPACT [34%Full] 2093056 total, 732400 used, 1360656 free
FVMAIN [99%Full] 3730240 total, 3730216 used, 24 free

In other words, it turns CLANG35 from a pathetic outlier into
something usable :-)

Regards,
Ard.

  reply	other threads:[~2016-08-01 14:10 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1469618762-7648-1-git-send-email-ard.biesheuvel@linaro.org>
2016-08-01 11:53 ` [PATCH 1/2] BaseTools/GenFw AARCH64: convert ADRP to ADR if binary size allows it Ard Biesheuvel
2016-08-01 14:09   ` Gao, Liming [this message]
2016-08-01 14:19   ` Leif Lindholm
2016-08-02  9:03     ` Ard Biesheuvel

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