[edk2-devel] [PATCH 1/1] BaseTools/GenFw AARCH64: disregard ADRP instructions that are patched already

[Ard Biesheuvel]

On Fri, 8 Nov 2019 at 01:39, Gao, Liming <liming.gao at intel.com> wrote:
>
> Acked-by: Liming Gao <liming.gao at intel.com>
>

Thanks all

Pushed as 9e9f0be353d4..f55c76b301f1

> >-----Original Message-----
> >From: devel at edk2.groups.io [mailto:devel at edk2.groups.io] On Behalf Of Ard
> >Biesheuvel
> >Sent: Thursday, November 07, 2019 5:06 PM
> >To: devel at edk2.groups.io
> >Cc: eugene at hp.com; Ard Biesheuvel <ard.biesheuvel at linaro.org>
> >Subject: [edk2-devel] [PATCH 1/1] BaseTools/GenFw AARCH64: disregard
> >ADRP instructions that are patched already
> >
> >In order to permit the use of compilers that only implement the small
> >code model [which involves the use of ADRP instructions that require
> >4 KB segment alignment] for generating PE/COFF binaries with a small
> >footprint, we patch ADRP instructions into ADR instructions while doing
> >the ELF to PE/COFF conversion.
> >
> >As it turns out, the linker may be doing the same, but for different
> >reasons: there is a silicon erratum #843419 for ARM Cortex-A53 which
> >affects ADRP instructions appearing at a certain offset in memory, and
> >one of the mitigations for this erratum is to patch them into ADR
> >instructions at link time if the symbol reference is within -/+ 1 MB.
> >However, the LD linker fails to update the static relocation tables, and
> >so we end up with an ADR instruction in the fully linked binary, but
> >with a relocation entry in the RELA section identifying it as an ADRP
> >instruction.
> >
> >Since the linker has already updated the symbol reference, there is no
> >handling needed in GenFw for such instructions, and we can simply treat
> >it as an ordinary ADR. However, since it is guaranteed to be accompanied
> >by an add or load instruction with a LO12 relocation referencing the same
> >symbol, the section offset check we apply to ADR instructions is going to
> >take place anyway, so we can just disregard the ADR instruction entirely.
> >
> >Reported-by: Eugene Cohen <eugene at hp.com>
> >Suggested-by: Eugene Cohen <eugene at hp.com>
> >Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> >---
> > BaseTools/Source/C/GenFw/Elf64Convert.c | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> >diff --git a/BaseTools/Source/C/GenFw/Elf64Convert.c
> >b/BaseTools/Source/C/GenFw/Elf64Convert.c
> >index d574300ac4fe..d623dce1f9da 100644
> >--- a/BaseTools/Source/C/GenFw/Elf64Convert.c
> >+++ b/BaseTools/Source/C/GenFw/Elf64Convert.c
> >@@ -1044,6 +1044,19 @@ WriteSections64 (
> >             /* fall through */
> >
> >           case R_AARCH64_ADR_PREL_PG_HI21:
> >+            //
> >+            // In order to handle Cortex-A53 erratum #843419, the LD linker may
> >+            // convert ADRP instructions into ADR instructions, but without
> >+            // updating the static relocation type, and so we may end up here
> >+            // while the instruction in question is actually ADR. So let's
> >+            // just disregard it: the section offset check we apply below to
> >+            // ADR instructions will trigger for its R_AARCH64_xxx_ABS_LO12_NC
> >+            // companion instruction as well, so it is safe to omit it here.
> >+            //
> >+            if ((*(UINT32 *)Targ & BIT31) == 0) {
> >+              break;
> >+            }
> >+
> >             //
> >             // AArch64 PG_H21 relocations are typically paired with ABS_LO12
> >             // relocations, where a PC-relative reference with +/- 4 GB range is
> >--
> >2.17.1
> >
> >
> >
>

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