docs: convert build system documentation to rST

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2020-08-11 18:34:40 +02:00
parent 77d27b9271
commit a14f0bf165
2 changed files with 137 additions and 164 deletions

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@ -1,5 +1,6 @@
The QEMU build system architecture
==================================
==================================
The QEMU build system architecture
==================================
This document aims to help developers understand the architecture of the
QEMU build system. As with projects using GNU autotools, the QEMU build
@ -26,7 +27,7 @@ Because QEMU uses the Meson build system under the hood, only VPATH
builds are supported. There are two general ways to invoke configure &
perform a build:
- VPATH, build artifacts outside of QEMU source tree entirely
- VPATH, build artifacts outside of QEMU source tree entirely::
cd ../
mkdir build
@ -34,7 +35,7 @@ perform a build:
../qemu/configure
make
- VPATH, build artifacts in a subdir of QEMU source tree
- VPATH, build artifacts in a subdir of QEMU source tree::
mkdir build
cd build
@ -52,21 +53,21 @@ following tasks:
- Add a Meson build option to meson_options.txt.
- Add support to the command line arg parser to handle any new
--enable-XXX / --disable-XXX flags required by the feature XXX.
`--enable-XXX`/`--disable-XXX` flags required by the feature.
- Add information to the help output message to report on the new
feature flag.
- Add code to perform the actual feature check.
- Add code to include the feature status in config-host.h
- Add code to include the feature status in `config-host.h`
- Add code to print out the feature status in the configure summary
upon completion.
Taking the probe for SDL as an example, we have the following pieces
in configure:
in configure::
# Initial variable state
sdl=auto
@ -89,11 +90,11 @@ in configure:
# Meson invocation
-Dsdl=$sdl
In meson_options.txt:
In meson_options.txt::
option('sdl', type : 'feature', value : 'auto')
In meson.build:
In meson.build::
# Detect dependency
sdl = dependency('sdl2',
@ -114,63 +115,51 @@ Helper functions
The configure script provides a variety of helper functions to assist
developers in checking for system features:
- do_cc $ARGS...
`do_cc $ARGS...`
Attempt to run the system C compiler passing it $ARGS...
- do_cxx $ARGS...
`do_cxx $ARGS...`
Attempt to run the system C++ compiler passing it $ARGS...
- compile_object $CFLAGS
`compile_object $CFLAGS`
Attempt to compile a test program with the system C compiler using
$CFLAGS. The test program must have been previously written to a file
called $TMPC.
- compile_prog $CFLAGS $LDFLAGS
`compile_prog $CFLAGS $LDFLAGS`
Attempt to compile a test program with the system C compiler using
$CFLAGS and link it with the system linker using $LDFLAGS. The test
program must have been previously written to a file called $TMPC.
- has $COMMAND
`has $COMMAND`
Determine if $COMMAND exists in the current environment, either as a
shell builtin, or executable binary, returning 0 on success.
- path_of $COMMAND
`path_of $COMMAND`
Return the fully qualified path of $COMMAND, printing it to stdout,
and returning 0 on success.
- check_define $NAME
`check_define $NAME`
Determine if the macro $NAME is defined by the system C compiler
- check_include $NAME
`check_include $NAME`
Determine if the include $NAME file is available to the system C
compiler
- write_c_skeleton
`write_c_skeleton`
Write a minimal C program main() function to the temporary file
indicated by $TMPC
- feature_not_found $NAME $REMEDY
`feature_not_found $NAME $REMEDY`
Print a message to stderr that the feature $NAME was not available
on the system, suggesting the user try $REMEDY to address the
problem.
- error_exit $MESSAGE $MORE...
`error_exit $MESSAGE $MORE...`
Print $MESSAGE to stderr, followed by $MORE... and then exit from the
configure script with non-zero status
- query_pkg_config $ARGS...
`query_pkg_config $ARGS...`
Run pkg-config passing it $ARGS. If QEMU is doing a static build,
then --static will be automatically added to $ARGS
@ -182,9 +171,13 @@ The Meson build system is currently used to describe the build
process for:
1) executables, which include:
- Tools - qemu-img, qemu-nbd, qga (guest agent), etc
- System emulators - qemu-system-$ARCH
- Userspace emulators - qemu-$ARCH
- Some (but not all) unit tests
2) documentation
@ -200,9 +193,9 @@ to list the files and their dependency on various configuration
symbols.
Various subsystems that are common to both tools and emulators have
their own sourceset, for example block_ss for the block device subsystem,
chardev_ss for the character device subsystem, etc. These sourcesets
are then turned into static libraries as follows:
their own sourceset, for example `block_ss` for the block device subsystem,
`chardev_ss` for the character device subsystem, etc. These sourcesets
are then turned into static libraries as follows::
libchardev = static_library('chardev', chardev_ss.sources(),
name_suffix: 'fa',
@ -210,7 +203,7 @@ are then turned into static libraries as follows:
chardev = declare_dependency(link_whole: libchardev)
The special ".fa" suffix is needed as long as unit tests are built with
The special `.fa` suffix is needed as long as unit tests are built with
the older Makefile infrastructure, and will go away later.
Files linked into emulator targets there can be split into two distinct groups
@ -221,24 +214,24 @@ In the target-independent set lives various general purpose helper code,
such as error handling infrastructure, standard data structures,
platform portability wrapper functions, etc. This code can be compiled
once only and the .o files linked into all output binaries.
Target-independent code lives in the common_ss, softmmu_ss and user_ss
sourcesets. common_ss is linked into all emulators, softmmu_ss only
in system emulators, user_ss only in user-mode emulators.
Target-independent code lives in the `common_ss`, `softmmu_ss` and
`user_ss` sourcesets. `common_ss` is linked into all emulators, `softmmu_ss`
only in system emulators, `user_ss` only in user-mode emulators.
In the target-dependent set lives CPU emulation, device emulation and
much glue code. This sometimes also has to be compiled multiple times,
once for each target being built.
All binaries link with a static library libqemuutil.a, which is then
linked to all the binaries. libqemuutil.a is built from several
All binaries link with a static library `libqemuutil.a`, which is then
linked to all the binaries. `libqemuutil.a` is built from several
sourcesets; most of them however host generated code, and the only two
of general interest are util_ss and stub_ss.
of general interest are `util_ss` and `stub_ss`.
The separation between these two is purely for documentation purposes.
util_ss contains generic utility files. Even though this code is only
`util_ss` contains generic utility files. Even though this code is only
linked in some binaries, sometimes it requires hooks only in some of
these and depend on other functions that are not fully implemented by
all QEMU binaries. stub_ss links dummy stubs that will only be linked
all QEMU binaries. `stub_ss` links dummy stubs that will only be linked
into the binary if the real implementation is not present. In a way,
the stubs can be thought of as a portable implementation of the weak
symbols concept.
@ -246,45 +239,43 @@ symbols concept.
The following files concur in the definition of which files are linked
into each emulator:
- default-configs/*.mak
`default-configs/*.mak`
The files under default-configs/ control what emulated hardware is built
into each QEMU system and userspace emulator targets. They merely contain
a list of config variable definitions like the machines that should be
included. For example, default-configs/aarch64-softmmu.mak has::
The files under default-configs/ control what emulated hardware is built
into each QEMU system and userspace emulator targets. They merely contain
a list of config variable definitions like the machines that should be
included. For example, default-configs/aarch64-softmmu.mak has:
include arm-softmmu.mak
CONFIG_XLNX_ZYNQMP_ARM=y
CONFIG_XLNX_VERSAL=y
include arm-softmmu.mak
CONFIG_XLNX_ZYNQMP_ARM=y
CONFIG_XLNX_VERSAL=y
`*/Kconfig`
These files are processed together with `default-configs/*.mak` and
describe the dependencies between various features, subsystems and
device models. They are described in kconfig.rst.
These files rarely need changing unless new devices / hardware need to
be enabled for a particular system/userspace emulation target
- */Kconfig
These files are processed together with default-configs/*.mak and
describe the dependencies between various features, subsystems and
device models. They are described in kconfig.rst.
Support scripts
---------------
Meson has a special convention for invoking Python scripts: if their
first line is "#! /usr/bin/env python3" and the file is *not* executable,
first line is `#! /usr/bin/env python3` and the file is *not* executable,
find_program() arranges to invoke the script under the same Python
interpreter that was used to invoke Meson. This is the most common
and preferred way to invoke support scripts from Meson build files,
because it automatically uses the value of configure's --python= option.
In case the script is not written in Python, use a "#! /usr/bin/env ..."
In case the script is not written in Python, use a `#! /usr/bin/env ...`
line and make the script executable.
Scripts written in Python, where it is desirable to make the script
executable (for example for test scripts that developers may want to
invoke from the command line, such as tests/qapi-schema/test-qapi.py),
should be invoked through the "python" variable in meson.build. For
example:
should be invoked through the `python` variable in meson.build. For
example::
test('QAPI schema regression tests', python,
args: files('test-qapi.py'),
@ -307,35 +298,35 @@ rules and wraps them so that e.g. submodules are built before QEMU.
The resulting build system is largely non-recursive in nature, in
contrast to common practices seen with automake.
Tests are also ran by the Makefile with the traditional "make check"
phony target. Meson test suites such as "unit" can be ran with "make
check-unit" too. It is also possible to run tests defined in meson.build
with "meson test".
Tests are also ran by the Makefile with the traditional `make check`
phony target. Meson test suites such as `unit` can be ran with `make
check-unit` too. It is also possible to run tests defined in meson.build
with `meson test`.
The following text is only relevant for unit tests which still have to
be converted to Meson.
All binaries should link to libqemuutil.a, e.g.:
All binaries should link to `libqemuutil.a`, e.g.:
qemu-img$(EXESUF): qemu-img.o ..snip.. libqemuutil.a
On Windows, all binaries have the suffix '.exe', so all Makefile rules
On Windows, all binaries have the suffix `.exe`, so all Makefile rules
which create binaries must include the $(EXESUF) variable on the binary
name. e.g.
qemu-img$(EXESUF): qemu-img.o ..snip..
This expands to '.exe' on Windows, or '' on other platforms.
This expands to `.exe` on Windows, or an empty string on other platforms.
Variable naming
---------------
The QEMU convention is to define variables to list different groups of
object files. These are named with the convention $PREFIX-obj-y. The
Meson "chardev" variable in the previous example corresponds to a
Meson `chardev` variable in the previous example corresponds to a
variable 'chardev-obj-y'.
Likewise, tests that are executed by "make check-unit" are grouped into
Likewise, tests that are executed by `make check-unit` are grouped into
a variable check-unit-y, like this:
check-unit-y += tests/test-visitor-serialization$(EXESUF)
@ -355,8 +346,8 @@ On Windows this expands to
check-unit-n += tests/vmstate.exe
Since the "check-unit" target only runs tests included in "$(check-unit-y)",
POSIX specific tests listed in $(util-obj-n) are ignored on the Windows
Since the `check-unit` target only runs tests included in `$(check-unit-y)`,
POSIX specific tests listed in `$(util-obj-n)` are ignored on the Windows
platform builds.
@ -397,47 +388,37 @@ The following key files are statically defined in the source tree, with
the rules needed to build QEMU. Their behaviour is influenced by a
number of dynamically created files listed later.
- Makefile
`Makefile`
The main entry point used when invoking make to build all the components
of QEMU. The default 'all' target will naturally result in the build of
every component. Makefile takes care of recursively building submodules
directly via a non-recursive set of rules.
The main entry point used when invoking make to build all the components
of QEMU. The default 'all' target will naturally result in the build of
every component. Makefile takes care of recursively building submodules
directly via a non-recursive set of rules.
`*/meson.build`
The meson.build file in the root directory is the main entry point for the
Meson build system, and it coordinates the configuration and build of all
executables. Build rules for various subdirectories are included in
other meson.build files spread throughout the QEMU source tree.
- Makefile.objs
`rules.mak`
This file provides the generic helper rules for invoking build tools, in
particular the compiler and linker.
Defines *-obj-y files corresponding to
`tests/Makefile.include`
Rules for building the unit tests. This file is included directly by the
top level Makefile, so anything defined in this file will influence the
entire build system. Care needs to be taken when writing rules for tests
to ensure they only apply to the unit test execution / build.
- */meson.build
`tests/docker/Makefile.include`
Rules for Docker tests. Like tests/Makefile, this file is included
directly by the top level Makefile, anything defined in this file will
influence the entire build system.
The meson.build file in the root directory is the main entry point for the
Meson build system, and it coordinates the configuration and build of all
executables. Build rules for various subdirectories are included in
other meson.build files spread throughout the QEMU source tree.
- rules.mak
This file provides the generic helper rules for invoking build tools, in
particular the compiler and linker.
- tests/Makefile.include
Rules for building the unit tests. This file is included directly by the
top level Makefile, so anything defined in this file will influence the
entire build system. Care needs to be taken when writing rules for tests
to ensure they only apply to the unit test execution / build.
- tests/docker/Makefile.include
Rules for Docker tests. Like tests/Makefile, this file is included
directly by the top level Makefile, anything defined in this file will
influence the entire build system.
- tests/vm/Makefile.include
Rules for VM-based tests. Like tests/Makefile, this file is included
directly by the top level Makefile, anything defined in this file will
influence the entire build system.
`tests/vm/Makefile.include`
Rules for VM-based tests. Like tests/Makefile, this file is included
directly by the top level Makefile, anything defined in this file will
influence the entire build system.
Dynamically created files
-------------------------
@ -450,79 +431,70 @@ Makefile.
Built by configure:
- config-host.mak
`config-host.mak`
When configure has determined the characteristics of the build host it
will write a long list of variables to config-host.mak file. This
provides the various install directories, compiler / linker flags and a
variety of `CONFIG_*` variables related to optionally enabled features.
This is imported by the top level Makefile and meson.build in order to
tailor the build output.
When configure has determined the characteristics of the build host it
will write a long list of variables to config-host.mak file. This
provides the various install directories, compiler / linker flags and a
variety of CONFIG_* variables related to optionally enabled features.
This is imported by the top level Makefile and meson.build in order to
tailor the build output.
config-host.mak is also used as a dependency checking mechanism. If make
sees that the modification timestamp on configure is newer than that on
config-host.mak, then configure will be re-run.
config-host.mak is also used as a dependency checking mechanism. If make
sees that the modification timestamp on configure is newer than that on
config-host.mak, then configure will be re-run.
The variables defined here are those which are applicable to all QEMU
build outputs. Variables which are potentially different for each
emulator target are defined by the next file...
The variables defined here are those which are applicable to all QEMU
build outputs. Variables which are potentially different for each
emulator target are defined by the next file...
- $TARGET-NAME/config-target.mak
TARGET-NAME is the name of a system or userspace emulator, for example,
x86_64-softmmu denotes the system emulator for the x86_64 architecture.
This file contains the variables which need to vary on a per-target
basis. For example, it will indicate whether KVM or Xen are enabled for
the target and any other potential custom libraries needed for linking
the target.
`$TARGET-NAME/config-target.mak`
TARGET-NAME is the name of a system or userspace emulator, for example,
x86_64-softmmu denotes the system emulator for the x86_64 architecture.
This file contains the variables which need to vary on a per-target
basis. For example, it will indicate whether KVM or Xen are enabled for
the target and any other potential custom libraries needed for linking
the target.
Built by Meson:
- ${TARGET-NAME}-config-devices.mak
`${TARGET-NAME}-config-devices.mak`
TARGET-NAME is again the name of a system or userspace emulator. The
config-devices.mak file is automatically generated by make using the
scripts/make_device_config.sh program, feeding it the
default-configs/$TARGET-NAME file as input.
TARGET-NAME is again the name of a system or userspace emulator. The
config-devices.mak file is automatically generated by make using the
scripts/make_device_config.sh program, feeding it the
default-configs/$TARGET-NAME file as input.
`config-host.h`, `$TARGET-NAME/config-target.h`, `$TARGET-NAME/config-devices.h`
These files are used by source code to determine what features
are enabled. They are generated from the contents of the corresponding
`*.h` files using the scripts/create_config program. This extracts
relevant variables and formats them as C preprocessor macros.
- config-host.h
- $TARGET-NAME/config-target.h
- $TARGET-NAME/config-devices.h
These files are used by source code to determine what features
are enabled. They are generated from the contents of the corresponding
*.h files using the scripts/create_config program. This extracts
relevant variables and formats them as C preprocessor macros.
- build.ninja
`build.ninja`
The build rules.
Built by Makefile:
- Makefile.ninja:
`Makefile.ninja`
A Makefile conversion of the build rules in build.ninja. The conversion
is straightforward and, were it necessary to debug the rules produced
by Meson, it should be enough to look at build.ninja. The conversion
is performed by scripts/ninjatool.py.
A Makefile conversion of the build rules in build.ninja. The conversion
is straightforward and, were it necessary to debug the rules produced
by Meson, it should be enough to look at build.ninja. The conversion
is performed by scripts/ninjatool.py.
- Makefile.mtest:
The Makefile definitions that let "make check" run tests defined in
meson.build. The rules are produced from Meson's JSON description of
tests (obtained with "meson introspect --tests") through the script
scripts/mtest2make.py.
`Makefile.mtest`
The Makefile definitions that let "make check" run tests defined in
meson.build. The rules are produced from Meson's JSON description of
tests (obtained with "meson introspect --tests") through the script
scripts/mtest2make.py.
Useful make targets
===================
- help
-------------------
`help`
Print a help message for the most common build targets.
- print-VAR
`print-VAR`
Print the value of the variable VAR. Useful for debugging the build
system.

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@ -13,6 +13,7 @@ Contents:
.. toctree::
:maxdepth: 2
build-system
kconfig
loads-stores
memory