Re: [PATCH 3/8] unwind: add sframe v2 header

[Prasanna Kumar T S M <ptsm@linux.microsoft.com>]

On 28-01-2025 03:03, Weinan Liu wrote:
> Add sframe header so that we know how to access the sframe section
> generated by compilers.
>
> This is the sframe header file borrowed from the patchset [1]
> Josh Poimboeuf according to sframe v2 spec [2].
>
> [1]: https://lore.kernel.org/lkml/42c0a99236af65c09c8182e260af7bcf5aa1e158.1730150953.git.jpoimboe@kernel.org/
> [2]: https://sourceware.org/binutils/docs/sframe-spec.html
>
> Signed-off-by: Weinan Liu <wnliu@google.com>
> ---
>   kernel/sframe.h | 215 ++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 215 insertions(+)
>   create mode 100644 kernel/sframe.h
>
> diff --git a/kernel/sframe.h b/kernel/sframe.h
> new file mode 100644
> index 000000000000..11b9be7ad82e
> --- /dev/null
> +++ b/kernel/sframe.h
> @@ -0,0 +1,215 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Copyright (C) 2023, Oracle and/or its affiliates.
> + *
> + * This file contains definitions for the SFrame stack tracing format, which is
> + * documented at https://sourceware.org/binutils/docs
> + */
> +#ifndef _SFRAME_H
> +#define _SFRAME_H
> +
> +#include <linux/types.h>
> +
> +#define SFRAME_VERSION_1	1
> +#define SFRAME_VERSION_2	2
> +#define SFRAME_MAGIC		0xdee2
> +
> +/* Function Descriptor Entries are sorted on PC. */
> +#define SFRAME_F_FDE_SORTED	0x1
> +/* Frame-pointer based stack tracing. Defined, but not set. */
> +#define SFRAME_F_FRAME_POINTER	0x2
> +
> +#define SFRAME_CFA_FIXED_FP_INVALID 0
> +#define SFRAME_CFA_FIXED_RA_INVALID 0
> +
> +/* Supported ABIs/Arch. */
> +#define SFRAME_ABI_AARCH64_ENDIAN_BIG	    1 /* AARCH64 big endian. */
> +#define SFRAME_ABI_AARCH64_ENDIAN_LITTLE    2 /* AARCH64 little endian. */
> +#define SFRAME_ABI_AMD64_ENDIAN_LITTLE	    3 /* AMD64 little endian. */
> +
> +/* SFrame FRE types. */
> +#define SFRAME_FRE_TYPE_ADDR1	0
> +#define SFRAME_FRE_TYPE_ADDR2	1
> +#define SFRAME_FRE_TYPE_ADDR4	2
> +
> +/*
> + * SFrame Function Descriptor Entry types.
> + *
> + * The SFrame format has two possible representations for functions. The
> + * choice of which type to use is made according to the instruction patterns
> + * in the relevant program stub.
> + */
> +
> +/* Unwinders perform a (PC >= FRE_START_ADDR) to look up a matching FRE. */
> +#define SFRAME_FDE_TYPE_PCINC	0
> +/*
> + * Unwinders perform a (PC & FRE_START_ADDR_AS_MASK >= FRE_START_ADDR_AS_MASK)
> + * to look up a matching FRE. Typical usecases are pltN entries, trampolines
> + * etc.
> + */
> +#define SFRAME_FDE_TYPE_PCMASK	1
> +
> +/**
> + * struct sframe_preamble - SFrame Preamble.
> + * @magic: Magic number (SFRAME_MAGIC).
> + * @version: Format version number (SFRAME_VERSION).
> + * @flags: Various flags.
> + */
> +struct sframe_preamble {
> +	u16 magic;
> +	u8  version;
> +	u8  flags;
> +} __packed;
> +
> +/**
> + * struct sframe_header - SFrame Header.
> + * @preamble: SFrame preamble.
> + * @abi_arch: Identify the arch (including endianness) and ABI.
> + * @cfa_fixed_fp_offset: Offset for the Frame Pointer (FP) from CFA may be
> + *	  fixed for some ABIs ((e.g, in AMD64 when -fno-omit-frame-pointer is
> + *	  used). When fixed, this field specifies the fixed stack frame offset
> + *	  and the individual FREs do not need to track it. When not fixed, it
> + *	  is set to SFRAME_CFA_FIXED_FP_INVALID, and the individual FREs may
> + *	  provide the applicable stack frame offset, if any.
> + * @cfa_fixed_ra_offset: Offset for the Return Address from CFA is fixed for
> + *	  some ABIs. When fixed, this field specifies the fixed stack frame
> + *	  offset and the individual FREs do not need to track it. When not
> + *	  fixed, it is set to SFRAME_CFA_FIXED_FP_INVALID.
> + * @auxhdr_len: Number of bytes making up the auxiliary header, if any.
> + *	  Some ABI/arch, in the future, may use this space for extending the
> + *	  information in SFrame header. Auxiliary header is contained in bytes
> + *	  sequentially following the sframe_header.
> + * @num_fdes: Number of SFrame FDEs in this SFrame section.
> + * @num_fres: Number of SFrame Frame Row Entries.
> + * @fre_len:  Number of bytes in the SFrame Frame Row Entry section.
> + * @fdes_off: Offset of SFrame Function Descriptor Entry section.
> + * @fres_off: Offset of SFrame Frame Row Entry section.
> + */
> +struct sframe_header {
> +	struct sframe_preamble preamble;
> +	u8  abi_arch;
> +	s8  cfa_fixed_fp_offset;
> +	s8  cfa_fixed_ra_offset;
> +	u8  auxhdr_len;
> +	u32 num_fdes;
> +	u32 num_fres;
> +	u32 fre_len;
> +	u32 fdes_off;
> +	u32 fres_off;
> +} __packed;
> +
> +#define SFRAME_HDR_SIZE(sframe_hdr)	\
> +	((sizeof(struct sframe_header) + (sframe_hdr).auxhdr_len))
> +
> +/* Two possible keys for executable (instruction) pointers signing. */
> +#define SFRAME_AARCH64_PAUTH_KEY_A    0 /* Key A. */
> +#define SFRAME_AARCH64_PAUTH_KEY_B    1 /* Key B. */
> +
> +/**
> + * struct sframe_fde - SFrame Function Descriptor Entry.
> + * @start_addr: Function start address. Encoded as a signed offset,
> + *	  relative to the current FDE.
> + * @size: Size of the function in bytes.
> + * @fres_off: Offset of the first SFrame Frame Row Entry of the function,
> + *	  relative to the beginning of the SFrame Frame Row Entry sub-section.
> + * @fres_num: Number of frame row entries for the function.
> + * @info: Additional information for deciphering the stack trace
> + *	  information for the function. Contains information about SFrame FRE
> + *	  type, SFrame FDE type, PAC authorization A/B key, etc.
> + * @rep_size: Block size for SFRAME_FDE_TYPE_PCMASK
> + * @padding: Unused
> + */
> +struct sframe_fde {
> +	s32 start_addr;
> +	u32 size;
> +	u32 fres_off;
> +	u32 fres_num;
> +	u8  info;
> +	u8  rep_size;
> +	u16 padding;
> +} __packed;
> +
> +/*
> + * 'func_info' in SFrame FDE contains additional information for deciphering
> + * the stack trace information for the function. In V1, the information is
> + * organized as follows:
> + *   - 4-bits: Identify the FRE type used for the function.
> + *   - 1-bit: Identify the FDE type of the function - mask or inc.
> + *   - 1-bit: PAC authorization A/B key (aarch64).
> + *   - 2-bits: Unused.
> + * ---------------------------------------------------------------------
> + * |  Unused  |  PAC auth A/B key (aarch64) |  FDE type |   FRE type   |
> + * |          |        Unused (amd64)       |           |              |
> + * ---------------------------------------------------------------------
> + * 8          6                             5           4              0
> + */
> +
> +/* Note: Set PAC auth key to SFRAME_AARCH64_PAUTH_KEY_A by default.  */
> +#define SFRAME_FUNC_INFO(fde_type, fre_enc_type) \
> +	(((SFRAME_AARCH64_PAUTH_KEY_A & 0x1) << 5) | \
> +	 (((fde_type) & 0x1) << 4) | ((fre_enc_type) & 0xf))
> +
> +#define SFRAME_FUNC_FRE_TYPE(data)	  ((data) & 0xf)
> +#define SFRAME_FUNC_FDE_TYPE(data)	  (((data) >> 4) & 0x1)
> +#define SFRAME_FUNC_PAUTH_KEY(data)	  (((data) >> 5) & 0x1)
> +
> +/*
> + * Size of stack frame offsets in an SFrame Frame Row Entry. A single
> + * SFrame FRE has all offsets of the same size. Offset size may vary
> + * across frame row entries.
> + */
> +#define SFRAME_FRE_OFFSET_1B	  0
> +#define SFRAME_FRE_OFFSET_2B	  1
> +#define SFRAME_FRE_OFFSET_4B	  2
> +
> +/* An SFrame Frame Row Entry can be SP or FP based.  */
> +#define SFRAME_BASE_REG_FP	0
> +#define SFRAME_BASE_REG_SP	1
> +
> +/*
> + * The index at which a specific offset is presented in the variable length
> + * bytes of an FRE.
> + */
> +#define SFRAME_FRE_CFA_OFFSET_IDX   0
> +/*
> + * The RA stack offset, if present, will always be at index 1 in the variable
> + * length bytes of the FRE.
> + */
> +#define SFRAME_FRE_RA_OFFSET_IDX    1
> +/*
> + * The FP stack offset may appear at offset 1 or 2, depending on the ABI as RA
> + * may or may not be tracked.
> + */
> +#define SFRAME_FRE_FP_OFFSET_IDX    2
> +
> +/*
> + * 'fre_info' in SFrame FRE contains information about:
> + *   - 1 bit: base reg for CFA
> + *   - 4 bits: Number of offsets (N). A value of up to 3 is allowed to track
> + *   all three of CFA, FP and RA (fixed implicit order).
> + *   - 2 bits: information about size of the offsets (S) in bytes.
> + *     Valid values are SFRAME_FRE_OFFSET_1B, SFRAME_FRE_OFFSET_2B,
> + *     SFRAME_FRE_OFFSET_4B
> + *   - 1 bit: Mangled RA state bit (aarch64 only).
> + * ---------------------------------------------------------------
> + * | Mangled-RA (aarch64) |  Size of   |   Number of  | base_reg |
> + * |  Unused (amd64)      |  offsets   |    offsets   |          |
> + * ---------------------------------------------------------------
> + * 8                      7             5             1          0
> + */
> +
> +/* Note: Set mangled_ra_p to zero by default. */
> +#define SFRAME_FRE_INFO(base_reg_id, offset_num, offset_size) \
> +	(((0 & 0x1) << 7) | (((offset_size) & 0x3) << 5) | \
> +	 (((offset_num) & 0xf) << 1) | ((base_reg_id) & 0x1))
> +
> +/* Set the mangled_ra_p bit as indicated. */
> +#define SFRAME_FRE_INFO_UPDATE_MANGLED_RA_P(mangled_ra_p, fre_info) \
> +	((((mangled_ra_p) & 0x1) << 7) | ((fre_info) & 0x7f))
> +
> +#define SFRAME_FRE_CFA_BASE_REG_ID(data)	  ((data) & 0x1)
> +#define SFRAME_FRE_OFFSET_COUNT(data)		  (((data) >> 1) & 0xf)
> +#define SFRAME_FRE_OFFSET_SIZE(data)		  (((data) >> 5) & 0x3)
> +#define SFRAME_FRE_MANGLED_RA_P(data)		  (((data) >> 7) & 0x1)
> +
> +#endif /* _SFRAME_H */

Looks good to me.

Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>.