Message-ID: <fe8a45e3-dfb1-84fc-8912-9cff257e6f1f@arm.com>
Date:   Wed, 24 Apr 2019 16:16:26 +0000
From:   Raphael Gault <Raphael.Gault@....com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <Will.Deacon@....com>,
        Julien Thierry <Julien.Thierry@....com>
Subject: Re: [RFC 2/6] objtool: arm64: Add required implementation for
 supporting the aarch64 architecture in objtool.

On 4/23/19 9:18 PM, Josh Poimboeuf wrote:
> On Tue, Apr 09, 2019 at 02:52:39PM +0100, Raphael Gault wrote:
>> Provide implementation for the arch-dependent functions that are called by the main check
>> function of objtool.
>> The ORC unwinder is not yet supported by the arm64 architecture so we only provide a dummy
>> interface for now.
>> The decoding of the instruction is split into classes and subclasses as described into
>> the Instruction Encoding in the ArmV8.5 Architecture Reference Manual.
>
> Where did the code for the decoder come from?  Was it written from
> scratch?
>

This decoder was indeed written from scratch based on the armv8 ARM. The
automatic generation idea hasn't really been discussed yet.

>> diff --git a/tools/objtool/arch/arm64/include/arch_special.h b/tools/objtool/arch/arm64/include/arch_special.h
>> new file mode 100644
>> index 000000000000..54bcce4c58c0
>> --- /dev/null
>> +++ b/tools/objtool/arch/arm64/include/arch_special.h
>> @@ -0,0 +1,44 @@
>> +/*
>> + * This program is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU General Public License
>> + * as published by the Free Software Foundation; either version 2
>> + * of the License, or (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
>> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
>> + */
>> +
>
> Needs a header guard.
>
>> +#define EX_ENTRY_SIZE8
>> +#define EX_ORIG_OFFSET0
>> +#define EX_NEW_OFFSET4
>> +
>> +#define JUMP_ENTRY_SIZE16
>> +#define JUMP_ORIG_OFFSET0
>> +#define JUMP_NEW_OFFSET4
>> +
>> +#define ALT_ENTRY_SIZE12
>> +#define ALT_ORIG_OFFSET0
>> +#define ALT_NEW_OFFSET4
>> +#define ALT_FEATURE_OFFSET8
>> +#define ALT_ORIG_LEN_OFFSET10
>> +#define ALT_NEW_LEN_OFFSET11
>> +
>> +/*
>> + * On arm64 the .altinstr_replacement is not always marked
>> + * as containing executable instruction. But we still want
>> + * to process it so we ignore the SHF_EXEC flag
>> + */
>> +#define IGNORE_SHF_EXEC_FLAG1
>> +
>> +/*
>> + * The jump table detection is not the same on arm64 so for
>> + * now we just detect if it is a dynamic jump (br <Xn> insn)
>> + */
>> +#define JUMP_DYNAMIC_IS_SWITCH_TABLE1
>
> Same as for x86, these flags should be added in the same patch which
> uses them.
>

This will disappear in the next version, thanks.

>> +
>> +#define X86_FEATURE_POPCNT (4*32+23)
>> diff --git a/tools/objtool/arch/arm64/include/asm/orc_types.h b/tools/objtool/arch/arm64/include/asm/orc_types.h
>> new file mode 100644
>> index 000000000000..46f516dd80ce
>> --- /dev/null
>> +++ b/tools/objtool/arch/arm64/include/asm/orc_types.h
>> @@ -0,0 +1,109 @@
>> +/*
>> + * Copyright (C) 2017 Josh Poimboeuf <jpoimboe@...hat.com>
>> + *
>> + * This program is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU General Public License
>> + * as published by the Free Software Foundation; either version 2
>> + * of the License, or (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
>> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
>> + */
>> +
>> +#ifndef _ORC_TYPES_H
>> +#define _ORC_TYPES_H
>> +
>> +#include <linux/types.h>
>> +#include <linux/compiler.h>
>> +
>> +/*
>> + * The ORC_REG_* registers are base registers which are used to find other
>> + * registers on the stack.
>> + *
>> + * ORC_REG_PREV_SP, also known as DWARF Call Frame Address (CFA), is the
>> + * address of the previous frame: the caller's SP before it called the current
>> + * function.
>> + *
>> + * ORC_REG_UNDEFINED means the corresponding register's value didn't change in
>> + * the current frame.
>> + *
>> + * The most commonly used base registers are SP and BP -- which the previous SP
>> + * is usually based on -- and PREV_SP and UNDEFINED -- which the previous BP is
>> + * usually based on.
>> + *
>> + * The rest of the base registers are needed for special cases like entry code
>> + * and GCC realigned stacks.
>> + */
>> +#define ORC_REG_UNDEFINED0
>> +#define ORC_REG_PREV_SP1
>> +#define ORC_REG_DX2
>> +#define ORC_REG_DI3
>> +#define ORC_REG_BP4
>> +#define ORC_REG_SP5
>> +#define ORC_REG_R106
>> +#define ORC_REG_R137
>> +#define ORC_REG_BP_INDIRECT8
>> +#define ORC_REG_SP_INDIRECT9
>> +#define ORC_REG_MAX15
>> +
>> +/*
>> + * ORC_TYPE_CALL: Indicates that sp_reg+sp_offset resolves to PREV_SP (the
>> + * caller's SP right before it made the call).  Used for all callable
>> + * functions, i.e. all C code and all callable asm functions.
>> + *
>> + * ORC_TYPE_REGS: Used in entry code to indicate that sp_reg+sp_offset points
>> + * to a fully populated pt_regs from a syscall, interrupt, or exception.
>> + *
>> + * ORC_TYPE_REGS_IRET: Used in entry code to indicate that sp_reg+sp_offset
>> + * points to the iret return frame.
>> + *
>> + * The UNWIND_HINT macros are used only for the unwind_hint struct.  They
>> + * aren't used in struct orc_entry due to size and complexity constraints.
>> + * Objtool converts them to real types when it converts the hints to orc
>> + * entries.
>> + */
>> +#define ORC_TYPE_CALL0
>> +#define ORC_TYPE_REGS1
>> +#define ORC_TYPE_REGS_IRET2
>> +#define UNWIND_HINT_TYPE_SAVE3
>> +#define UNWIND_HINT_TYPE_RESTORE4
>> +
>> +#ifndef __ASSEMBLY__
>> +/*
>> + * This struct is more or less a vastly simplified version of the DWARF Call
>> + * Frame Information standard.  It contains only the necessary parts of DWARF
>> + * CFI, simplified for ease of access by the in-kernel unwinder.  It tells the
>> + * unwinder how to find the previous SP and BP (and sometimes entry regs) on
>> + * the stack for a given code address.  Each instance of the struct corresponds
>> + * to one or more code locations.
>> + */
>> +struct orc_entry {
>> +s16sp_offset;
>> +s16bp_offset;
>> +unsignedsp_reg:4;
>> +unsignedbp_reg:4;
>> +unsignedtype:2;
>> +unsignedend:1;
>> +} __packed;
>> +
>> +/*
>> + * This struct is used by asm and inline asm code to manually annotate the
>> + * location of registers on the stack for the ORC unwinder.
>> + *
>> + * Type can be either ORC_TYPE_* or UNWIND_HINT_TYPE_*.
>> + */
>> +struct unwind_hint {
>> +u32ip;
>> +s16sp_offset;
>> +u8sp_reg;
>> +u8type;
>> +u8end;
>> +};
>> +#endif /* __ASSEMBLY__ */
>> +
>> +#endif /* _ORC_TYPES_H */
>
> It seems odd to have the above header file in arm64 code, since it
> doesn't implement ORC.  Is it really needed?
>

The unwind_hint part can safely be removed. However the orc_entry seems
to be needed since the struct instruction comports a struct orc_entry
field. I have chosen to let it here as well but maybe a better approach
is possible.

Cheers,

--
Raphael Gault
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