Re: [RFC 2/6] objtool: arm64: Add required implementation for supporting the aarch64 architecture in objtool.

Josh Poimboeuf
2019-04-23T20:18:37Z

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?

> 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_SIZE 8
> +#define EX_ORIG_OFFSET 0
> +#define EX_NEW_OFFSET 4
> +
> +#define JUMP_ENTRY_SIZE 16
> +#define JUMP_ORIG_OFFSET 0
> +#define JUMP_NEW_OFFSET 4
> +
> +#define ALT_ENTRY_SIZE 12
> +#define ALT_ORIG_OFFSET 0
> +#define ALT_NEW_OFFSET 4
> +#define ALT_FEATURE_OFFSET 8
> +#define ALT_ORIG_LEN_OFFSET 10
> +#define ALT_NEW_LEN_OFFSET 11
> +
> +/*
> + * 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_FLAG 1
> +
> +/*
> + * 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_TABLE 1

Same as for x86, these flags should be added in the same patch which
uses them.

> +
> +#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@redhat.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_UNDEFINED 0
> +#define ORC_REG_PREV_SP 1
> +#define ORC_REG_DX 2
> +#define ORC_REG_DI 3
> +#define ORC_REG_BP 4
> +#define ORC_REG_SP 5
> +#define ORC_REG_R10 6
> +#define ORC_REG_R13 7
> +#define ORC_REG_BP_INDIRECT 8
> +#define ORC_REG_SP_INDIRECT 9
> +#define ORC_REG_MAX 15
> +
> +/*
> + * 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_CALL 0
> +#define ORC_TYPE_REGS 1
> +#define ORC_TYPE_REGS_IRET 2
> +#define UNWIND_HINT_TYPE_SAVE 3
> +#define UNWIND_HINT_TYPE_RESTORE 4
> +
> +#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 {
> + s16 sp_offset;
> + s16 bp_offset;
> + unsigned sp_reg:4;
> + unsigned bp_reg:4;
> + unsigned type:2;
> + unsigned end: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 {
> + u32 ip;
> + s16 sp_offset;
> + u8 sp_reg;
> + u8 type;
> + u8 end;
> +};
> +#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?

--
Josh