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ldgen: additional documentations re. internal workings

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Renz Bagaporo 2021-03-05 17:49:10 +08:00
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7 changed files with 248 additions and 29 deletions
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42
tools/ldgen/README.md Normal file
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@ -0,0 +1,42 @@
## Linker Script Generator
Contains code that implements linker script generation, `ldgen`. For more information about the feature,
see `docs/en/api-guides/linker-script-generation.rst`.
### Source Files
The following are the source files in the directory:
- `ldgen.py` - Python executable that gets called during build.
- `entity.py` - contains classes related to entities (library, object, symbol or combination of the above) with mappable input sections.
- `fragments.py` - contains classes for parsing the different types of fragments in linker fragment files.
- `generation.py` - contains bulk of the logic used to process fragments into output commands.
- `sdkconfig.py` - used for evaluating conditionals in fragment files.
- `linker_script.py` - augments the input linker script template with output commands from generation process to produce the output linker script.
- `output_commands.py` - contains classes that represent the output commands in the output linker script.
- `ldgen_common.py` - contains miscellaneous utilities/definitions that can be used in the files mentioned above.
### Tests
Unit tests are in the `test` directory. These tests are run as part of CI in the job `test_ldgen_on_host`.
There is also a test app for `ldgen` in `tools/test_apps/build_system/ldgen_test`.
### Build System
Linker script generation is a part of the build process. The build scripts `tools/cmake/ldgen.cmake`
and `make/ldgen.mk` contain the build-system-side implementation for CMake and Make, respectively.
### Basic Flow
The build system invokes `ldgen.py`, passing some information from the build.
The linker fragment files are parsed by `fragments.py`, evaluating conditional expressions
with `sdkconfig.py`.
From the parsed fragments, `generation.py` generates output commands defined in `output_commands.py`,
with some help from `entity.py`.
`linker_script.py` writes the output linker script, replacing markers with output commands generated.
More details about the implementation are in the respective source files.

15
tools/ldgen/entity.py
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@ -27,8 +27,13 @@ from pyparsing import (Group, Literal, OneOrMore, ParseException, SkipTo, Suppre
@total_ordering
class Entity():
"""
Definition of an entity which can be placed or excluded
from placement.
An entity refers to a library, object, symbol whose input
sections can be placed or excluded from placement.
An important property of an entity is its specificity - the granularity
of the the entity to be placed. Specificity increases in the following
order: library, object, symbol. An entity with no specificity refers
to all entities.
"""
ALL = '*'
@ -105,8 +110,10 @@ class Entity():
class EntityDB():
"""
Encapsulates an output of objdump. Contains information about the static library sections
and names
Collection of entities extracted from libraries known in the build.
Allows retrieving a list of archives, a list of object files in an archive
or a list of symbols in an archive; as well as allows for checking if an
entity exists in the collection.
"""
__info = collections.namedtuple('__info', 'filename content')

98
tools/ldgen/fragments.py
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@ -26,11 +26,11 @@ from pyparsing import (Combine, Forward, Group, Keyword, Literal, OneOrMore, Opt
from sdkconfig import SDKConfig
class FragmentFile():
"""
Fragment file internal representation. Parses and stores instances of the fragment definitions
contained within the file.
Processes a fragment file and stores all parsed fragments. For
more information on how this class interacts with classes for the different fragment types,
see description of Fragment.
"""
def __init__(self, fragment_file, sdkconfig):
@ -185,11 +185,34 @@ class FragmentFile():
class Fragment():
"""
Base class for a fragment that can be parsed from a fragment file. All fragments
share the common grammar:
[type:name]
key1:value1
key2:value2
...
Supporting a new fragment type means deriving a concrete class which specifies
key-value pairs that the fragment supports and what to do with the parsed key-value pairs.
The new fragment must also be appended to FRAGMENT_TYPES, specifying the
keyword for the type and the derived class.
The key of the key-value pair is a simple keyword string. Other parameters
that describe the key-value pair is specified in Fragment.KeyValue:
1. grammar - pyparsing grammar to parse the value of key-value pair
2. min - the minimum number of value in the key entry, None means no minimum
3. max - the maximum number of value in the key entry, None means no maximum
4. required - if the key-value pair is required in the fragment
Setting min=max=1 means that the key has a single value.
FragmentFile provides conditional expression evaluation, enforcing
the parameters for Fragment.Keyvalue.
"""
__metaclass__ = abc.ABCMeta
"""
Encapsulates a fragment as defined in the generator syntax. Sets values common to all fragment and performs processing
such as checking the validity of the fragment name and getting the entry values.
"""
KeyValue = namedtuple('KeyValue', 'grammar min max required')
@ -206,6 +229,15 @@ class Fragment():
class Sections(Fragment):
"""
Fragment which contains list of input sections.
[sections:<name>]
entries:
.section1
.section2
...
"""
# Unless quoted, symbol names start with a letter, underscore, or point
# and may include any letters, underscores, digits, points, and hyphens.
@ -248,12 +280,19 @@ class Sections(Fragment):
class Scheme(Fragment):
"""
Encapsulates a scheme fragment, which defines what target input sections are placed under.
Fragment which defines where the input sections defined in a Sections fragment
is going to end up, the target. The targets are markers in a linker script template
(see LinkerScript in linker_script.py).
[scheme:<name>]
entries:
sections1 -> target1
...
"""
grammars = {
'entries': Fragment.KeyValue(Fragment.IDENTIFIER.setResultsName('sections') + Suppress('->') +
Fragment.IDENTIFIER.setResultsName('target'), 1, None, True)
Fragment.IDENTIFIER.setResultsName('target'), 1, None, True)
}
def set_key_value(self, key, parse_results):
@ -268,7 +307,23 @@ class Scheme(Fragment):
class Mapping(Fragment):
"""
Encapsulates a mapping fragment, which defines what targets the input sections of mappable entties are placed under.
Fragment which attaches a scheme to entities (see Entity in entity.py), specifying where the input
sections of the entity will end up.
[mapping:<name>]
archive: lib1.a
entries:
obj1:symbol1 (scheme1); section1 -> target1 KEEP SURROUND(sym1) ...
obj2 (scheme2)
...
Ultimately, an `entity (scheme)` entry generates an
input section description (see https://sourceware.org/binutils/docs/ld/Input-Section.html)
in the output linker script. It is possible to attach 'flags' to the
`entity (scheme)` to generate different output commands or to
emit additional keywords in the generated input section description. The
input section description, as well as other output commands, is defined in
output_commands.py.
"""
class Flag():
@ -276,7 +331,6 @@ class Mapping(Fragment):
Optional(Suppress(',') + Suppress('post').setParseAction(lambda: True).setResultsName('post')))
class Surround(Flag):
def __init__(self, symbol):
self.symbol = symbol
self.pre = True
@ -286,7 +340,7 @@ class Mapping(Fragment):
def get_grammar():
# SURROUND(symbol)
#
# __symbol_start, __symbol_end is generated before and after
# '__symbol_start', '__symbol_end' is generated before and after
# the corresponding input section description, respectively.
grammar = (Keyword('SURROUND').suppress() +
Suppress('(') +
@ -309,7 +363,11 @@ class Mapping(Fragment):
@staticmethod
def get_grammar():
# ALIGN(alignment, [, pre, post])
# ALIGN(alignment, [, pre, post]).
#
# Generates alignment command before and/or after the corresponding
# input section description, depending whether pre, post or
# both are specified.
grammar = (Keyword('ALIGN').suppress() +
Suppress('(') +
Word(nums).setResultsName('alignment') +
@ -344,6 +402,9 @@ class Mapping(Fragment):
@staticmethod
def get_grammar():
# KEEP()
#
# Surrounds input section description with KEEP command.
grammar = Keyword('KEEP()').setParseAction(Mapping.Keep)
return grammar
@ -362,7 +423,12 @@ class Mapping(Fragment):
@staticmethod
def get_grammar():
# SORT(sort_by_first [, sort_by_second])
# SORT([sort_by_first, sort_by_second])
#
# where sort_by_first, sort_by_second = {name, alignment, init_priority}
#
# Emits SORT_BY_NAME, SORT_BY_ALIGNMENT or SORT_BY_INIT_PRIORITY
# depending on arguments. Nested sort follows linker script rules.
keywords = Keyword('name') | Keyword('alignment') | Keyword('init_priority')
grammar = (Keyword('SORT').suppress() + Suppress('(') +
keywords.setResultsName('first') +
@ -458,7 +524,9 @@ class Mapping(Fragment):
class DeprecatedMapping():
"""
Encapsulates a mapping fragment, which defines what targets the input sections of mappable entties are placed under.
Mapping fragment with old grammar in versions older than ESP-IDF v4.0. Does not conform to
requirements of the Fragment class and thus is limited when it comes to conditional expression
evaluation.
"""
# Name of the default condition entry

81
tools/ldgen/generation.py
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@ -26,6 +26,26 @@ from output_commands import AlignAtAddress, InputSectionDesc, SymbolAtAddress
class Placement():
"""
A Placement is an assignment of an entity's input sections to a target
in the output linker script - a precursor to the input section description.
A placement can be excluded from another placement. These are represented
as contents of EXCLUDE_FILE in the input section description. Since the linker uses the
first matching rule, these exclusions make sure that accidental matching
of entities with higher specificity does not occur.
The placement which a placement is excluded from is referred to as the
'basis' placement. It operates on the same input section of the entity on
one of the parent (or parent's parent and so forth), but might have
a different target (see is_significant() for the criteria).
A placement is explicit if it was derived from an actual entry in one of
the mapping fragments. Just as intermediate entity nodes are created in some cases,
intermediate placements are created particularly for symbol placements.
The reason is that EXCLUDE_FILE does not work on symbols (see ObjectNode
for details).
"""
def __init__(self, node, sections, target, flags, explicit, force=False, dryrun=False):
self.node = node
@ -43,9 +63,7 @@ class Placement():
# fragment entry.
self.explicit = explicit
# Find basis placement. A basis placement is a placement
# on the parent (or parent's parent and so on and so forth)
# that operates on the same section as this one.
# Find basis placement.
parent = node.parent
candidate = None
while parent:
@ -91,6 +109,31 @@ class Placement():
class EntityNode():
"""
Node in entity tree. An EntityNode
is created from an Entity (see entity.py).
The entity tree has a maximum depth of 3. Nodes at different
depths are derived from this class for special behavior (see
RootNode, ArchiveNode, ObjectNode, SymbolNode) depending
on entity specificity.
Nodes for entities are inserted at the appropriate depth, creating
intermediate nodes along the path if necessary. For example, a node
for entity `lib1.a:obj1:sym1` needs to be inserted. If the node for `lib1:obj1`
does not exist, then it needs to be created.
A node contains a dictionary of placements (see Placement).
The key to this dictionary are contents of sections fragments,
representing the input sections of an entity. For example,
a node for entity `lib1.a` might have a placement entry for its `.text` input section
in this dictionary. The placement will contain details about the
target, the flags, etc.
Generation of output commands to be written to the output linker script
requires traversal of the tree, each node collecting the output commands
from its children, so on and so forth.
"""
def __init__(self, parent, name):
self.children = []
@ -212,14 +255,32 @@ class EntityNode():
class SymbolNode(EntityNode):
"""
Entities at depth=3. Represents entities with archive, object
and symbol specified.
"""
def __init__(self, parent, name):
EntityNode.__init__(self, parent, name)
self.entity = Entity(self.parent.parent.name, self.parent.name)
class ObjectNode(EntityNode):
"""
Entities at depth=2. Represents entities with archive
and object specified.
Creating a placement on a child node (SymbolNode) has a different behavior, since
exclusions using EXCLUDE_FILE for symbols does not work.
The sections of this entity has to be 'expanded'. That is, we must
look into the actual input sections of this entity and remove
the ones corresponding to the symbol. The remaining sections of an expanded
object entity will be listed one-by-one in the corresponding
input section description.
An intermediate placement on this node is created, if one does not exist,
and is the one excluded from its basis placement.
"""
def __init__(self, parent, name):
EntityNode.__init__(self, parent, name)
self.child_t = SymbolNode
@ -281,7 +342,9 @@ class ObjectNode(EntityNode):
class ArchiveNode(EntityNode):
"""
Entities at depth=1. Represents entities with archive specified.
"""
def __init__(self, parent, name):
EntityNode.__init__(self, parent, name)
self.child_t = ObjectNode
@ -289,6 +352,10 @@ class ArchiveNode(EntityNode):
class RootNode(EntityNode):
"""
Single entity at depth=0. Represents entities with no specific members
specified.
"""
def __init__(self):
EntityNode.__init__(self, None, Entity.ALL)
self.child_t = ArchiveNode
@ -297,7 +364,9 @@ class RootNode(EntityNode):
class Generation:
"""
Implements generation of placement based on collected sections, scheme and mapping fragment.
Processes all fragments processed from fragment files included in the build.
Generates output commands (see output_commands.py) that LinkerScript (see linker_script.py) can
write to the output linker script.
"""
# Processed mapping, scheme and section entries

7
tools/ldgen/linker_script.py
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@ -24,8 +24,11 @@ from pyparsing import ParseException, Suppress, White
class LinkerScript:
"""
Encapsulates a linker script template file. Finds marker syntax and handles replacement to generate the
final output.
Process a linker script template, which contains markers with grammar:
[<target>]
The <target> is where output commands (see output_commands.py) are placed.
"""
Marker = collections.namedtuple('Marker', 'target indent rules')

30
tools/ldgen/output_commands.py
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@ -16,8 +16,20 @@
from entity import Entity
# Contains classes for output section commands referred to in
# https://www.acrc.bris.ac.uk/acrc/RedHat/rhel-ld-en-4/sections.html#OUTPUT-SECTION-DESCRIPTION.
class AlignAtAddress():
"""
Outputs assignment of builtin function ALIGN to current
position:
. = ALIGN(<alignment>)
Mapping fragment flag ALIGN causes this output section
command to be emitted.
"""
def __init__(self, alignment):
self.alignment = alignment
@ -31,6 +43,16 @@ class AlignAtAddress():
class SymbolAtAddress():
"""
Outputs assignment of builtin function ABSOLUTE to a symbol
for current position:
<symbol> = ABSOLUTE(.)
Mapping fragment flag SURROUND causes this
output section command to be emitted before and after
an InputSectionDesc.
"""
def __init__(self, symbol):
self.symbol = symbol
@ -44,6 +66,14 @@ class SymbolAtAddress():
class InputSectionDesc():
"""
Outputs an input section description as described in
https://www.acrc.bris.ac.uk/acrc/RedHat/rhel-ld-en-4/sections.html#INPUT-SECTION.
These commands are emmited from mapping fragment entries, specifically attaching
a scheme onto an entity. Mapping fragment flags KEEP, SORT will also affect
the emitted input section description.
"""
def __init__(self, entity, sections, exclusions=None, keep=False, sort=None):
assert(entity.specificity != Entity.Specificity.SYMBOL)

4
tools/ldgen/sdkconfig.py
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@ -21,8 +21,8 @@ from pyparsing import (Combine, Group, Literal, Optional, Word, alphanums, hexnu
class SDKConfig:
"""
Encapsulates an sdkconfig file. Defines grammar of a configuration entry, and enables
evaluation of logical expressions involving those entries.
Evaluates conditional expressions based on the build's sdkconfig and Kconfig files.
This also defines the grammar of conditional expressions.
"""
# A configuration entry is in the form CONFIG=VALUE. Definitions of components of that grammar