freesea
/
data
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
data/method/gdb/gdb-13.2/libsframe/doc/sframe-spec.info

620 lines
26 KiB
Plaintext
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

This is sframe-spec.info, produced by makeinfo version 6.8 from
sframe-spec.texi.
Copyright (C) 2021-2022 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU General Public License, Version 3 or any
later version published by the Free Software Foundation. A copy of the
license is included in the section entitled "GNU General Public
License".
INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* SFrame: (sframe-spec). The Simple Frame format.
END-INFO-DIR-ENTRY

File: sframe-spec.info, Node: Top, Next: Overview, Up: (dir)
The SFrame format
*****************
This manual describes version 1 of the SFrame file format. SFrame
stands for Simple Frame format. SFrame format keeps track of the
minimal necessary information needed for stack unwinding:
- Canonical Frame Address (CFA).
- Frame Pointer (FP).
- Return Address (RA).
The reason for existence of the SFrame format is to support fast,
online backtracing using a simple unwinder.
* Menu:
* Overview::
* SFrame section::
* Index::

File: sframe-spec.info, Node: Overview, Next: SFrame section, Prev: Top, Up: Top
Overview
********
The SFrame unwind information is provided in a loaded section, known as
the '.sframe' section. When available, the '.sframe' section appears in
a new segment of its own, PT_GNU_SFRAME.
The SFrame format is currently supported only for select ABIs,
namely, AMD64 and AAPCS64.
The contents of the SFrame section are stored in the target
endianness, i.e., in the endianness of the system on which the section
is targetted to be used. An SFrame section reader may use the magic
number in the SFrame header to identify the endianness of the SFrame
section.
Addresses in this specification are expressed in bytes.
The associated API to decode, probe and encode the SFrame section,
provided via 'libsframe', is not accompanied here at this time. This
will be added later.
This document is intended to be in sync with the C code in
'sframe.h'. Please report descrepancies between the two, if any.

File: sframe-spec.info, Node: SFrame section, Next: Index, Prev: Overview, Up: Top
1 SFrame section
****************
The SFrame section consists of an SFrame header, starting with a
preamble, and two other sub-sections, namely the SFrame Function
Descriptor Entry (SFrame FDE) sub-section, and the SFrame Frame Row
Entry (SFrame FRE) sub-section.
* Menu:
* SFrame Preamble::
* SFrame Header::
* SFrame Function Descriptor Entries::
* SFrame Frame Row Entries::

File: sframe-spec.info, Node: SFrame Preamble, Next: SFrame Header, Up: SFrame section
1.1 SFrame Preamble
===================
The preamble is a 32-bit packed structure; the only part of the SFrame
whose format cannot vary between versions.
typedef struct sframe_preamble
{
uint16_t sfp_magic;
uint8_t sfp_version;
uint8_t sfp_flags;
} ATTRIBUTE_PACKED sframe_preamble;
All values are stored in the endianness of the target system for
which the SFrame section is intended. Further details:
Offset Name Description
-----------------------------------------------------------------------------------------
0x00 'uint16_t sfp_magic' The magic number for SFrame section: 0xdee2. Defined
as a macro 'SFRAME_MAGIC'.
0x02 'uint8_t sfp_version' The version number of this SFrame section.
*Note SFrame version::, for the set of valid values.
Current version is 'SFRAME_VERSION_1'.
0x03 'uint8_t sfp_flags' Flags (section-wide) for this SFrame section.
*Note SFrame flags::, for the set of valid values.
* Menu:
* SFrame endianness::
* SFrame version::
* SFrame flags::

File: sframe-spec.info, Node: SFrame endianness, Next: SFrame version, Up: SFrame Preamble
1.1.1 SFrame endianness
-----------------------
SFrame sections are stored in the target endianness of the system that
consumes them. The SFrame library ('libsframe') can, however, detect
whether to endian-flip an SFrame section at decode time, by inspecting
the 'sfp_magic' field in the SFrame header (If it appears as 0xe2de,
endian-flipping is needed).

File: sframe-spec.info, Node: SFrame version, Next: SFrame flags, Prev: SFrame endianness, Up: SFrame Preamble
1.1.2 SFrame version
--------------------
The version of the SFrame format can be determined by inspecting
'sfp_version'. The following versions are currently valid:
Version Number Description
----------------------------------------------------------------
'SFRAME_VERSION_1' 1 First version, under development.
This section documents 'SFRAME_VERSION_1'.

File: sframe-spec.info, Node: SFrame flags, Prev: SFrame version, Up: SFrame Preamble
1.1.3 SFrame flags
------------------
The preamble contains bitflags in its 'sfp_flags' field that describe
various section-wide properties.
The following flags are currently defined.
Flag Versions Value Meaning
----------------------------------------------------------------------------
'SFRAME_F_FDE_SORTED' All 0x1 Function Descriptor Entries
are sorted on PC.
'SFRAME_F_FRAME_POINTER' All 0x2 Functions preserve
frame-pointer.
Further flags may be added in future.

File: sframe-spec.info, Node: SFrame Header, Next: SFrame Function Descriptor Entries, Prev: SFrame Preamble, Up: SFrame section
1.2 SFrame Header
=================
The SFrame header is the first part of an SFrame section. It begins
with the SFrame preamble. All parts of it other than the preamble
(*note SFrame Preamble::) can vary between SFrame file versions. It
contains things that apply to the section as a whole, and offsets to the
various other sub-sections defined in the format. As with the rest of
the SFrame section, all values are stored in the endianness of the
target system.
The two sub-sections tile the SFrame section: each section runs from
the offset given until the start of the next section. An explicit
length is given for the last sub-section, the SFrame Frame Row Entry
(SFrame FRE) sub-section.
typedef struct sframe_header
{
sframe_preamble sfh_preamble;
uint8_t sfh_abi_arch;
int8_t sfh_cfa_fixed_fp_offset;
int8_t sfh_cfa_fixed_ra_offset;
uint8_t sfh_auxhdr_len;
uint32_t sfh_num_fdes;
uint32_t sfh_num_fres;
uint32_t sfh_fre_len;
uint32_t sfh_fdeoff;
uint32_t sfh_freoff;
} ATTRIBUTE_PACKED sframe_header;
The sub-section offsets, namely 'sfh_fdeoff' and 'sfh_freoff', in the
SFrame header are relative to the _end_ of the SFrame header; they are
each an offset in bytes into the SFrame section where the SFrame FDE
sub-section and the SFrame FRE sub-section respectively start.
SFrame header allows specifying explicitly the fixed offsets from
CFA, if any, from which FP or RA may be recovered. For example, in
AMD64, the stack offset of the return address is 'CFA - 8'. Since this
offset is in close vicinity with the CFA in most ABIs,
'sfh_cfa_fixed_fp_offset' and 'sfh_cfa_fixed_ra_offset' are limited to
signed 8-bit integers.
SFrame format has provisioned for future ABIs/architectures that it
may support. The 'sframe_header' structure provides an unsigned 8-bit
integral field to denote the size of an auxilliary SFrame header. The
auxilliary SFrame header follows right after the 'sframe_header'
structure. As for the offset calculations, the _end_ of SFrame header
must be the end of the auxilliary SFrame header, if the latter is
present.
Tieing it all together:
Offset Name Description
----------------------------------------------------------------------------------
0x00 'sframe_preamble sfh_preamble' The SFrame preamble.
*Note SFrame Preamble::.
0x04 'uint8_t sfh_abi_arch' The ABI/arch identifier.
*Note SFrame ABI/arch identifier::.
0x05 'int8_t sfh_cfa_fixed_fp_offset' The CFA fixed FP offset, if any.
0x06 'int8_t sfh_cfa_fixed_ra_offset' The CFA fixed RA offset, if any.
0x07 'uint8_t sfh_auxhdr_len' Size in bytes of the auxilliary
header that follows the
'sframe_header' structure.
0x08 'uint32_t sfh_num_fdes' The number of SFrame FDEs in the
section.
0xc 'uint32_t sfh_num_fres' The number of SFrame FREs in the
section.
0x10 'uint32_t sfh_fre_len' The length in bytes of the SFrame
FRE sub-section.
0x14 'uint32_t sfh_fdeoff' The offset in bytes of the SFrame
FDE sub-section. This sub-section
contains 'sfh_num_fdes' number of
fixed-length array elements. The
array element is of type SFrame
function desciptor entry, each
providing a high-level function
description for backtracing.
*Note SFrame Function Descriptor Entries::.
0x18 'uint32_t sfh_freoff' The offset in bytes of the SFrame
FRE sub-section, the core of the
SFrame section, which describes the
unwind information using
variable-length array elements.
*Note SFrame Frame Row Entries::.
* Menu:
* SFrame ABI/arch identifier::

File: sframe-spec.info, Node: SFrame ABI/arch identifier, Up: SFrame Header
1.2.1 SFrame ABI/arch identifier
--------------------------------
SFrame header identifies the ABI/arch of the target system for which the
executable and it's unwind information is intended. There are currently
three identifiable ABI/arch values in the format.
ABI/arch Identifier Value Description
---------------------------------------------------------------------
'SFRAME_ABI_AARCH64_ENDIAN_BIG' 1 AARCH64 big-endian
'SFRAME_ABI_AARCH64_ENDIAN_LITTLE' 2 AARCH64 little-endian
'SFRAME_ABI_AMD64_ENDIAN_LITTLE' 3 AMD64 little-endian
The presence of an explicit identification of ABI/arch in SFrame may
allow unwinders to make certain ABI-specific decisions.

File: sframe-spec.info, Node: SFrame Function Descriptor Entries, Next: SFrame Frame Row Entries, Prev: SFrame Header, Up: SFrame section
1.3 SFrame FDE
==============
The SFrame Function Descriptor Entry sub-section is a sorted array of
fixed-length SFrame function descriptor entries (SFrame FDEs). Each
SFrame FDE is a packed structure which contains information to describe
a function's unwind information at a high-level.
typedef struct sframe_func_desc_entry
{
int32_t sfde_func_start_address;
uint32_t sfde_func_size;
uint32_t sfde_func_start_fre_off;
uint32_t sfde_func_num_fres;
uint8_t sfde_func_info;
} ATTRIBUTE_PACKED sframe_func_desc_entry;
'sfde_func_start_fre_off' is the offset to the first SFrame FRE for
the function. This offset is relative to the _end of the SFrame FDE_
sub-section (unlike the offsets in the SFrame header, which are relative
to the _end_ of the SFrame header).
'sfde_func_info' is the "info word", containing information on the
FRE type and the FDE type for the function *Note The SFrame FDE info
word::.
Following table describes each component of the SFrame FDE structure:
Offset Name Description
------------------------------------------------------------------------------------
0x00 'int32_t sfde_func_start_address' Signed 32-bit integral field
denoting the virtual memory address
of the described function.
0x04 'uint32_t sfde_func_size' Unsigned 32-bit integral field
specifying the size of the function
in bytes.
0x08 'uint32_t sfde_func_start_fre_off' Unsigned 32-bit integral field
specifying the offset in bytes of
the function's first SFrame FRE in
the SFrame section.
0x0c 'uint32_t sfde_func_num_fres' Unsigned 32-bit integral field
specifying the total number of
SFrame FREs used for the function.
0x10 'uint8_t sfde_func_info' The SFrame FDE info word.
*Note The SFrame FDE info word::.
* Menu:
* The SFrame FDE info word::
* The SFrame FDE types::
* The SFrame FRE types::

File: sframe-spec.info, Node: The SFrame FDE info word, Next: The SFrame FDE types, Up: SFrame Function Descriptor Entries
1.3.1 The SFrame FDE info word
------------------------------
The info word is a bitfield split into three parts. From MSB to LSB:
Bit offset Name Description
------------------------------------------------------------------------------------------
7-5 'unused' Unused bits.
4 'fdetype' SFRAME_FDE_TYPE_PCMASK (1) or SFRAME_FDE_TYPE_PCINC (0).
*Note The SFrame FDE types::.
0-3 'fretype' Choice of three SFrame FRE types.
*Note The SFrame FRE types::.

File: sframe-spec.info, Node: The SFrame FDE types, Next: The SFrame FRE types, Prev: The SFrame FDE info word, Up: SFrame Function Descriptor Entries
1.3.2 The SFrame FDE types
--------------------------
SFrame format defines two types of FDE entries. The choice of which
SFrame FDE type to use is made based on the instruction patterns in the
relevant program stub.
An SFrame FDE of type 'SFRAME_FDE_TYPE_PCINC' is an indication that
the PCs in the FREs should be treated as increments in bytes. This is
used fo the the bulk of the executable code of a program, which contains
instructions with no specific pattern.
In contrast, an SFrame FDE of type 'SFRAME_FDE_TYPE_PCMASK' is an
indication that the PCs in the FREs should be treated as masks. This
type is useful for the cases where a small pattern of instructions in a
program stub is used repeatedly for a specific functionality. Typical
usecases are pltN entries and trampolines.
Name of SFrame FDE type Value Description
-------------------------------------------------------------------------------
SFRAME_FDE_TYPE_PCINC 0 Unwinders perform a (PC >= FRE_START_ADDR)
to look up a matching FRE.
SFRAME_FDE_TYPE_PCMASK 1 Unwinders perform a (PC &
FRE_START_ADDR_AS_MASK >=
FRE_START_ADDR_AS_MASK) to look up a
matching FRE.

File: sframe-spec.info, Node: The SFrame FRE types, Prev: The SFrame FDE types, Up: SFrame Function Descriptor Entries
1.3.3 The SFrame FRE types
--------------------------
A real world application can have functions of size big and small.
SFrame format defines three types of SFrame FRE entries to represent the
unwind information for such a variety of function sizes. These
representations vary in the number of bits needed to encode the start
address offset in the SFrame FRE.
The following constants are defined and used to identify the SFrame
FRE types:
Name Value Description
--------------------------------------------------------------------------
'SFRAME_FRE_TYPE_ADDR1' 0 The start address offset (in bytes)
of the SFrame FRE is an unsigned
8-bit value.
'SFRAME_FRE_TYPE_ADDR2' 1 The start address offset (in bytes)
of the SFrame FRE is an unsigned
16-bit value.
'SFRAME_FRE_TYPE_ADDR4' 2 The start address offset (in bytes)
of the SFrame FRE is an unsigned
32-bit value.
A single function must use the same type of FRE throughout. The
choice of which SFrame FRE is used to encode the unwind information of a
function, is stored in the *Note The SFrame FDE info word::.

File: sframe-spec.info, Node: SFrame Frame Row Entries, Prev: SFrame Function Descriptor Entries, Up: SFrame section
1.4 SFrame FRE
==============
The SFrame Frame Row Entry sub-section contains the core of the unwind
information.
An SFrame Frame Row Entry is a self-sufficient record containing
SFrame unwind info for a range of contiguous addresses, starting at the
specified offset from the start of the function. Each SFrame Frame Row
Entry is followed by S*N bytes, where:
- 'S' is the size of the stack frame offset for the FRE, and
- 'N' is the number of stack frame offsets in the FRE
The stack offsets, following the FRE, are interpreted in order as
follows:
- The first offset is always used to locate the CFA, by interpreting
it as: CFA = 'BASE_REG' + offset1.
- If RA is being tracked, the second offset is always used to locate
the RA, by interpreting it as: RA = CFA + offset2. If RA is _not_
being tracked _and_ FP is being tracked, the second offset will be
used to locate the FP, by interpreting it as: FP = CFA + offset2.
- If both RA and FP are being tracked, the third offset will be used
to locate the FP, by interpreting it as FP = CFA + offset3.
The entities 'S', 'N' and 'BASE_REG' are identified using the SFrame
FRE info word, a.k.a. the 'sframe_fre_info' *Note The SFrame FRE info
word::.
Following are the definitions of the allowed SFrame FRE:
typedef struct sframe_frame_row_entry_addr1
{
uint8_t sfre_start_address;
sframe_fre_info sfre_info;
} ATTRIBUTE_PACKED sframe_frame_row_entry_addr1;
typedef struct sframe_frame_row_entry_addr2
{
uint16_t sfre_start_address;
sframe_fre_info sfre_info;
} ATTRIBUTE_PACKED sframe_frame_row_entry_addr2;
typedef struct sframe_frame_row_entry_addr4
{
uint32_t sfre_start_address;
sframe_fre_info sfre_info;
} ATTRIBUTE_PACKED sframe_frame_row_entry_addr4;
'sfre_start_address' is an unsigned 8-bit/16-bit/32-bit integral
field identifies the start address of the range of program counters, for
which the SFrame FRE applies. The value encoded in the
'sfre_start_address' field is the offset in bytes of the start address
of the SFrame FRE, from the start address of the function.
Further FRE types may be added in future.
* Menu:
* The SFrame FRE info word::

File: sframe-spec.info, Node: The SFrame FRE info word, Up: SFrame Frame Row Entries
1.4.1 The SFrame FRE info word
------------------------------
The SFrame FRE info word is a bitfield split into four parts. From MSB
to LSB:
Bit offset Name Description
-------------------------------------------------------------------------------------
7 'fre_mangled_ra_p' Indicate whether the return address is
mangled with any authorization bits (signed
RA).
5-6 'fre_offset_size' Size of stack offsets in bytes. Valid values
are SFRAME_FRE_OFFSET_1B,
SFRAME_FRE_OFFSET_2B, and
SFRAME_FRE_OFFSET_4B.
1-4 'fre_offset_count' A value of upto 3 is allowed to track all
three of CFA, FP and RA.
0 'fre_cfa_base_reg_id' Distinguish between SP or FP based CFA
recovery.
Name Value Description
--------------------------------------------------------------------------------
'SFRAME_FRE_OFFSET_1B' 0 All stack offsets following the fixed-length
FRE structure are 1 byte long.
'SFRAME_FRE_OFFSET_2B' 1 All stack offsets following the fixed-length
FRE structure are 2 bytes long.
'SFRAME_FRE_OFFSET_4B' 2 All stack offsets following the fixed-length
FRE structure are 4 bytes long.

File: sframe-spec.info, Node: Index, Prev: SFrame section, Up: Top
Index
*****
[index]
* Menu:
* endianness: SFrame endianness. (line 6)
* Overview: Overview. (line 6)
* PT_GNU_SFRAME: Overview. (line 6)
* SFrame ABI/arch identifier: SFrame ABI/arch identifier.
(line 6)
* SFrame FDE: SFrame Function Descriptor Entries.
(line 6)
* SFrame flags: SFrame flags. (line 6)
* SFrame FRE: SFrame Frame Row Entries.
(line 6)
* SFrame header: SFrame Header. (line 6)
* SFrame preamble: SFrame Preamble. (line 6)
* SFrame section: SFrame section. (line 6)
* SFrame versions: SFrame version. (line 9)
* SFRAME_ABI_AARCH64_ENDIAN_BIG: SFrame ABI/arch identifier.
(line 12)
* SFRAME_ABI_AARCH64_ENDIAN_LITTLE: SFrame ABI/arch identifier.
(line 15)
* SFRAME_ABI_AMD64_ENDIAN_LITTLE: SFrame ABI/arch identifier.
(line 17)
* SFRAME_FDE_TYPE_PCINC: The SFrame FDE types. (line 6)
* SFRAME_FDE_TYPE_PCMASK: The SFrame FDE types. (line 6)
* SFRAME_FRE_OFFSET_1B: The SFrame FRE info word.
(line 29)
* SFRAME_FRE_OFFSET_2B: The SFrame FRE info word.
(line 33)
* SFRAME_FRE_OFFSET_4B: The SFrame FRE info word.
(line 36)
* SFRAME_FRE_TYPE_ADDR1: The SFrame FRE types. (line 17)
* SFRAME_FRE_TYPE_ADDR2: The SFrame FRE types. (line 22)
* SFRAME_FRE_TYPE_ADDR4: The SFrame FRE types. (line 26)
* SFRAME_F_FDE_SORTED: SFrame flags. (line 11)
* SFRAME_F_FRAME_POINTER: SFrame flags. (line 14)
* SFRAME_MAGIC: SFrame Preamble. (line 22)
* SFRAME_VERSION_1: SFrame version. (line 9)
* The SFrame FDE info word: SFrame Function Descriptor Entries.
(line 59)
* The SFrame FRE info word: SFrame Frame Row Entries.
(line 64)

Tag Table:
Node: Top564
Node: Overview1114
Node: SFrame section2135
Node: SFrame Preamble2607
Node: SFrame endianness3963
Node: SFrame version4419
Node: SFrame flags4921
Node: SFrame Header5641
Node: SFrame ABI/arch identifier10812
Node: SFrame Function Descriptor Entries11778
Node: The SFrame FDE info word14571
Node: The SFrame FDE types15296
Node: The SFrame FRE types16864
Node: SFrame Frame Row Entries18420
Node: The SFrame FRE info word20817
Node: Index22761

End Tag Table

Local Variables:
coding: utf-8
End:
Reference in New Issue View Git Blame Copy Permalink