[edk2-devel] [PATCH 3/5] GenGv: Arm: support images entered in Thumb mode
Ard Biesheuvel
ardb at kernel.org
Mon May 10 15:54:40 UTC 2021
On Tue, 4 May 2021 at 17:20, Etienne Carriere
<etienne.carriere at linaro.org> wrote:
>
> Change GenFv for Arm architecture to generate a specific jump
> instruction as image entry instruction, when the target entry label
> is assembled with Thumb instruction set. This is possible since
> SecCoreEntryAddress value fetched from the PE32 as its LSBit set when
> the entry instruction executes in Thumb mode.
>
> Cc: Bob Feng <bob.c.feng at intel.com>
> Cc: Liming Gao <gaoliming at byosoft.com.cn>
> Cc: Achin Gupta <achin.gupta at arm.com>
> Cc: Ard Biesheuvel <ardb+tianocore at kernel.org>
> Cc: Leif Lindholm <leif at nuviainc.com>
> Cc: Sughosh Ganu <sughosh.ganu at linaro.org>
> Signed-off-by: Etienne Carriere <etienne.carriere at linaro.org>
This looks fine to me (modulo a couple of typos: GenGv, enry) but this
needs an ack from the BaseTools maintainers.
Bob, Liming?
> ---
> BaseTools/Source/C/GenFv/GenFvInternalLib.c | 38 +++++++++++++++-----
> 1 file changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/BaseTools/Source/C/GenFv/GenFvInternalLib.c b/BaseTools/Source/C/GenFv/GenFvInternalLib.c
> index 6e296b8ad6..3af65146f6 100644
> --- a/BaseTools/Source/C/GenFv/GenFvInternalLib.c
> +++ b/BaseTools/Source/C/GenFv/GenFvInternalLib.c
> @@ -34,9 +34,27 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
> #include "FvLib.h"
> #include "PeCoffLib.h"
>
> -#define ARMT_UNCONDITIONAL_JUMP_INSTRUCTION 0xEB000000
> #define ARM64_UNCONDITIONAL_JUMP_INSTRUCTION 0x14000000
>
> +/*
> + * Arm instruction to jump to Fv enry instruction in Arm or Thumb mode.
> + * From ARM Arch Ref Manual versions b/c/d, section A8.8.25 BL, BLX (immediate)
> + * BLX (encoding A2) branches to offset in Thumb instruction set mode.
> + * BL (encoding A1) branches to offset in Arm instruction set mode.
> + */
> +#define ARM_JUMP_OFFSET_MAX 0xffffff
> +#define ARM_JUMP_TO_ARM(Offset) (0xeb000000 | ((Offset - 8) >> 2))
> +
> +#define _ARM_JUMP_TO_THUMB(Imm32) (0xfa000000 | \
> + (((Imm32) & (1 << 1)) << (24 - 1)) | \
> + (((Imm32) >> 2) & 0x7fffff))
> +#define ARM_JUMP_TO_THUMB(Offset) _ARM_JUMP_TO_THUMB((Offset) - 8)
> +
> +/*
> + * Arm instruction to retrun from exception (MOVS PC, LR)
> + */
> +#define ARM_RETURN_FROM_EXCEPTION 0xE1B0F07E
> +
> BOOLEAN mArm = FALSE;
> BOOLEAN mRiscV = FALSE;
> STATIC UINT32 MaxFfsAlignment = 0;
> @@ -2203,23 +2221,25 @@ Returns:
> // if we found an SEC core entry point then generate a branch instruction
> // to it and populate a debugger SWI entry as well
> if (UpdateVectorSec) {
> + UINT32 EntryOffset;
>
> VerboseMsg("UpdateArmResetVectorIfNeeded updating ARM SEC vector");
>
> - // B SecEntryPoint - signed_immed_24 part +/-32MB offset
> - // on ARM, the PC is always 8 ahead, so we're not really jumping from the base address, but from base address + 8
> - ResetVector[0] = (INT32)(SecCoreEntryAddress - FvInfo->BaseAddress - 8) >> 2;
> + EntryOffset = (INT32)(SecCoreEntryAddress - FvInfo->BaseAddress);
>
> - if (ResetVector[0] > 0x00FFFFFF) {
> - Error(NULL, 0, 3000, "Invalid", "SEC Entry point must be within 32MB of the start of the FV");
> + if (EntryOffset > ARM_JUMP_OFFSET_MAX) {
> + Error(NULL, 0, 3000, "Invalid", "SEC Entry point offset above 1MB of the start of the FV");
> return EFI_ABORTED;
> }
>
> - // Add opcode for an unconditional branch with no link. i.e.: " B SecEntryPoint"
> - ResetVector[0] |= ARMT_UNCONDITIONAL_JUMP_INSTRUCTION;
> + if (SecCoreEntryAddress & 1) {
> + ResetVector[0] = ARM_JUMP_TO_THUMB(EntryOffset);
> + } else {
> + ResetVector[0] = ARM_JUMP_TO_ARM(EntryOffset);
> + }
>
> // SWI handler movs pc,lr. Just in case a debugger uses SWI
> - ResetVector[2] = 0xE1B0F07E;
> + ResetVector[2] = ARM_RETURN_FROM_EXCEPTION;
>
> // Place holder to support a common interrupt handler from ROM.
> // Currently not supported. For this to be used the reset vector would not be in this FV
> --
> 2.17.1
>
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