The accuracy is greatly improved by using the C preprocessor to scan C
sources for presym. C preprocessor can perfectly interpret all comments and
preprocessor directives, so it can detect all symbols defined, for example
`mrbgems/mruby-socket/src/const.cstub`.
Also, as described later, this change will greatly improve the accuracy of
presym detection from Ruby sources.
## Result
The number of lines in the `presym` file for all gems is as follows:
```console
Previous: 999 (false positive = 89, undetected = 297)
New: 1207
```
## Build process
The new build process (with presym) is as follows:
1. Build `mrbc` without presym (more on building without presym later).
2. Compile Ruby sources to C struct format with the `mrbc` created in
step 1, and create` mrblib.c` and `gem_init.c`. Note that the symbols
in the created files are output as `MRB_SYM` family macros or
`mrb_intern_lit` instead of IDs (details will be described later).
3. C preprocessor processes C sources including the created files of
step 2 and outputs them as `.i` files. In these files, for example,
`MRB_IVSYM(foo)` is converted to `<@! "@" "foo" !@>` and
`mrb_define_module(mrb, "Foo")` is converted to `<@! "Foo" !@>`.
4. Scan the files created in step 3 and create `presym` and` presym.inc`
files.
The files created in step 2 should output all static symbols defined in Ruby
sources, including local variables, so we can detect all presyms by just
scanning C sources without scanning Ruby sources directly.
Further, by this process, the files to be scanned becomes the same as the
files to be compiled, so that there is no excess or deficiency.
## Related changes
The following changes have been made in relation to realizing this feature.
### Allow build without presym
It enables build without presym to achieve the "Build process: 1". This
incorporates #5202, see its issue for details.
Note that when presym is enabled, even adding a local variable to a Ruby
source may change contents of presym and require recompilation of almost
all C sources. This is inconvenient, especially during trial and error in
development, but this feature is also useful because it does not cause
this problem if presym is disabled.
### Automatically create build target for `mrbc` without presym
The `mrbc` used in the "Build process: 1" will be built by automatically
creating a build target for it. The build name is `SOURCE_BUILD_NAME/mrbc`.
### Constantize output of C struct format by `mrbc`
To realizing the "Build process: 2", as mentioned above, symbol IDs are not
output directly in C struct format output by `mrbc`. As a result, the output
becomes constant regardless of the state of presym at the time of `mrbc`
build, and it is possible to detect symbols of Ruby sources in the same way
as other C sources.
Note that `mrb_intern_lit` is used for symbols that do not become presym,
but in this state, the corresponding element in the symbol array cannot be
statically initialized, so it is initialized at run time (therefore, in this
case, the `const` qualifier is not added to the symbol array).
### Specify arbitrary `mrbc` file
To realizing the "Build process: 2", enabled to specify `mrbc` created by
another build target or pre-built` mrbc`. Use `MRuby::Build#mrbcfile =` to
specify it explicitly. You can omit the "Build process: 1" by specifying
pre-built `mrbc`, and you can always use an optimized build to compile Ruby
sources faster. I think changes that affect the output of `mrbc` are rare,
so in many cases it helps to improve efficiency.
With presym, the build will be a little slower due to more build steps, but
this feature will improve it a bit.
### Create presym files for each build target
This feature was proposed at #5194 and merged once, but was reverted in
5c205e6e due to problems especially with cross-compilation. It has been
introduced again because this change solves the problem.
The presym files will be created below.
* `build/NAME/presym`
* `build/NAME/include/mruby/presym.inc`
### Other changes
* Because presym detection accuracy is greatly improved as mentioned above,
`MRuby::Gem::Specification#cdump?` is set to true by default, and
`disable_cdump` is added instead of `enable_cdump`. Also, support for gem
specific presym files has been discontinued (https://github.com/mruby/mruby/issues/5151#issuecomment-730967232).
* Previously, `mrbc` was automatically created for the `host` build, but it
will not be created if the build target for `mrbc` mentioned above is
automatically created. At this time, `mrbc` file of the `mrbc` build is
copied to` bin/`.
* Two types of `.d` files will be created, `.o.d` and `.i.d`. oThis is
because if `.i` depends on `presym.inc`, the dependency will circulate, so
the `.d` file cannot be shared.
* Changed file created with `enable_cxx_exception` to `X-cxx.cxx` from
`X.cxx` to use the mruby standard Rake rule.
### Note
Almost all C sources will need to be recompiled if there are any changes to
`persym.inc` (if not recompiled properly, it will often result in run-time
error). If `gcc` toolchain is used, dependencies are resolved by the `.d`
file, so it become automatically recompile target, but if not (e.g. MSVC),
it is necessary to manually make it recompile target.
Also, even if `gcc` toolchain is used, it may not become recompile target if
external gems does not use the mruby standard Rake rule. In particular, if
the standard rule is overwritten, such as
https://github.com/mruby/mruby/pull/5112/files, `.d` file will not be read,
so be careful.
Previously, `libmruby.a` was created even if only `mruby-bin-mrbc` or`
mruby-compiler` was specified for gem, but by specifying `disable_libmruby`,
the creation of `libmruby.a` can be suppressed.
### Note
The https://github.com/mruby/mruby/pull/5084#issuecomment-723521971
incompatibility seems to be difficult for users to avoid, so the original
behavior has been restored. Therefore, if we need `mrbc` other than the
`host` build, we need to explicitly specify `mruby-bin-mrbc` gem.
Due to the above changes, `build_config/boxing.rb` etc. will not work, but I
have added` mruby-bin-mrbc` to `default.gembox` to fix it. I don't think
this change is a big deal because originally `mruby-compiler` was included.
Due to the above changes, it may not work with the existing build
configurations in cross-compilation (even if we can build without presym),
therefore revert it once (ref https://github.com/mruby/mruby/pull/5202#issuecomment-735412643). Sorry for the lack of consideration.
Previously, presym files were always created in `build/{presym,presym.inc}`.
However, this constraint is inconvenient because it is common to use
multiple build configurations and build targets in a single mruby tree.
Therefore, change to create presym file for each build target.
For example, in the case of the C++ compiler, it is output as
`CXX build/host/src/gc.cxx -> build/host/src/gc.cxx.o` (FYI, in the case
of `enable_cxx_abi`, it outputs `CC ...` because the option to compile as
C++ is added to C compiler).
* Output `GEN` log for generated files
* `MRBC` log is outputted one for each `mrbc` execution
#### Before this patch:
```console
CC src/array.c -> build/host/src/array.o
(snip)
GEN mrblib/*.rb -> build/host/mrblib/mrblib.c
MRBC mrblib/00class.rb
MRBC mrblib/10error.rb
(snip)
CC mrbgems/mruby-time/src/time.c -> build/host/mrbgems/mruby-time/src/time.o
MRBC mrbgems/mruby-time/mrblib/time.rb
(snip)
CC mrbgems/mruby-socket/test/sockettest.c -> build/host/mrbgems/mruby-socket/test/sockettest.o
MRBC mrbgems/mruby-socket/test/addrinfo.rb
MRBC mrbgems/mruby-socket/test/basicsocket.rb
(snip)
```
#### After this patch:
```console
GEN build/presym
GEN build/presym.inc
CC src/array.c -> build/host/src/array.o
(snip)
GEN mrblib/*.rb -> build/host/mrblib/mrblib.c
MRBC mrblib/00class.rb
mrblib/10error.rb
(snip)
CC mrbgems/mruby-time/src/time.c -> build/host/mrbgems/mruby-time/src/time.o
GEN build/host/mrbgems/mruby-time/gem_init.c
MRBC mrbgems/mruby-time/mrblib/time.rb
(snip)
CC mrbgems/mruby-socket/test/sockettest.c -> build/host/mrbgems/mruby-socket/test/sockettest.o
GEN build/host/mrbgems/mruby-socket/gem_test.c
MRBC mrbgems/mruby-socket/test/addrinfo.rb
MRBC mrbgems/mruby-socket/test/basicsocket.rb
(snip)
```
ref: https://github.com/mruby/mruby/pull/4959#discussion_r402086196
Compiles twice because it falls back to `build.filename(command)` when
`command` fails. This process was added at 9968af4 to support `ccache gcc`
etc. At that time, it seems that it was necessary because
`build.filename(command)` quoted the whole `command`, but now it does not
quote, so we can just run `build.filename(command)`.
### Example
```console
$ echo 1 > src/a.c
$ rake -v
```
#### Before this patch:
```console
(snip)
gcc -std=gnu99 -g -O3 -Wall -Wundef -Wdeclaration-after-statement -Werror-implicit-function-declaration -Wwrite-strings -I"/mruby/mruby/include" -MMD -o "/mruby/mruby/build/host/src/a.o" -c "/mruby/mruby/src/a.c"
/mruby/mruby/src/a.c:1:1: error: expected identifier or '('
1
^
1 error generated.
gcc -std=gnu99 -g -O3 -Wall -Wundef -Wdeclaration-after-statement -Werror-implicit-function-declaration -Wwrite-strings -I"/mruby/mruby/include" -MMD -o "/mruby/mruby/build/host/src/a.o" -c "/mruby/mruby/src/a.c"
/mruby/mruby/src/a.c:1:1: error: expected identifier or '('
1
^
1 error generated.
rake aborted!
(snip)
```
#### After this patch:
```console
(snip)
gcc -std=gnu99 -g -O3 -Wall -Wundef -Wdeclaration-after-statement -Werror-implicit-function-declaration -Wwrite-strings -I"/mruby/mruby/include" -MMD -o "/mruby/mruby/build/host/src/a.o" -c "/mruby/mruby/src/a.c"
/mruby/mruby/src/a.c:1:1: error: expected identifier or '('
1
^
1 error generated.
rake aborted!
(snip)
```
If you confirm the gem is cdump safe, add `spec.enable_cdump` in
`mrbgem.rake` file. Some external gems e.g. `mruby-mgem-template` do
not work with cdump.
It was relative from the directory of the build configuration file, but
the document says it's relative from `MRUBY_ROOT`. When the default
configuration file was `MRUBY_ROOT/build_config.rb`, it was OK for most
of the cases.
In addition, update the documents referring `build_config.rb` which is
no longer used. The new `build_config.rb` describes the new configuration
structure in the comment.
* In explanation of mruby, the expression `build_config.rb` is frequently
used including official documents, so I think that it will not make sense
if the file is no longer used.
* The `MRUBY_TARGET` mechanism seems to have little improvement, so I don't
think it should be changed to avoid unnecessary confusion.
* `MRUBY_TARGET` and `MRuby.targets` represent somewhat different things,
so using the same term "target" is a bit confusing.
The mechanism that can be written short when using a file under
`build_config` (renamed from `target`) directory remains
(`build_config/${MRUBY_CONFIG}.rb` is used if the path specified
in `MRUBY_CONFIG` doesn't exist).
Files under `test/t` and `mrbgem/*/test` are for tests, not for actual
execution. So symbols in those files need not to be pre-allocated. This
change slightly reduce the memory consumption.
You have to specify `TARGET` to specify a configuration, e.g.
```
rake TARGET=host-debug all test
```
When you port `mruby` to a new configuration:
1. copy an existing configuration under `target` directory
2. modify the new configuration file
3. build using the new configuration
4. send PR if you please
KOBAYASHI Shuji