Added complete documentation for all C API functions providing exception
handling capabilities in src/exception.c:
## Core C API Functions:
### Exception Protection:
- mrb_protect: executes function under exception protection, equivalent to
Ruby's begin/rescue blocks, catches exceptions and returns them as objects
with error state flag for C code exception handling
### Guaranteed Cleanup:
- mrb_ensure: executes function with guaranteed cleanup, equivalent to Ruby's
begin/ensure blocks, ensures cleanup function always runs regardless of
exceptions, re-raises caught exceptions after cleanup
### Exception Handling:
- mrb_rescue: executes function with StandardError exception handling,
convenience wrapper for common rescue patterns, automatically catches
StandardError and its subclasses
- mrb_rescue_exceptions: executes function with specific exception class
handling, allows selective exception catching based on class hierarchy,
re-raises unmatched exceptions for precise error control
## Helper Components:
### Internal Structures:
- protect_data: helper structure to pass function and data to protection
wrapper, encapsulates function pointer and argument data for safe execution
### Internal Functions:
- protect_body: helper function that wraps user function calls for exception
protection, extracts function and data from protect_data structure and
calls user function with proper parameters
Key features documented:
- Exception protection and propagation control
- Guaranteed cleanup execution (ensure semantics)
- Selective exception class handling with inheritance support
- Integration with mruby's exception system and GC
- C API patterns for robust error handling in extensions
Provides complete coverage of exception handling C API for robust error
management in mruby C extensions and embedded applications, essential
for building reliable C code that integrates with mruby's exception system.
Co-authored-by: Atlassian Rovo Dev
Running pre-commit with GitHub Actions now gives us more tests and coverage
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Add new custom pre-commit hook running with a shell script to sort alphabetically and uniquify codespell.txt
Add new pre-commit hook to check spelling with codespell
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Fix spelling
The purpose is two-fold:
1. to be able to specify a pointer directly when user data is used
When using `mrb_protect()`, it is necessary to allocate objects by `mrb_obj_cptr()` function when using user data.
Adding `mrb_protect_raw()` will make it simpler to reimplement `mrbgems/mruby-error`.
2. to correctly unwind callinfo when an exception is raised from a C function defined as a method (the main topic)
If a method call is made directly under `mrb_protect()` and a C function is called, control is returned from `mrb_protect()` if an exception occurs there.
In this case, callinfo is not restored, so it is out of sync.
Moreover, returning to mruby VM (`mrb_vm_exec()` function) in this state will indicate `ci->pc` of C function which is equal to `NULL`, and subsequent `JUMP` will cause `SIGSEGV`.
Following is an example that actually causes `SIGSEGV`:
- `crash.c`
```c
#include <mruby.h>
#include <mruby/compile.h>
#include <mruby/error.h>
static mrb_value
level1_body(mrb_state *mrb, mrb_value self)
{
return mrb_funcall(mrb, self, "level2", 0);
}
static mrb_value
level1(mrb_state *mrb, mrb_value self)
{
return mrb_protect(mrb, level1_body, self, NULL);
}
static mrb_value
level2(mrb_state *mrb, mrb_value self)
{
mrb_raise(mrb, E_RUNTIME_ERROR, "error!");
return mrb_nil_value();
}
int
main(int argc, char *argv[])
{
mrb_state *mrb = mrb_open();
mrb_define_method(mrb, mrb->object_class, "level1", level1, MRB_ARGS_NONE());
mrb_define_method(mrb, mrb->object_class, "level2", level2, MRB_ARGS_NONE());
mrb_p(mrb, mrb_load_string(mrb, "p level1"));
mrb_close(mrb);
return 0;
}
```
- compile & run
```console
% `bin/mruby-config --cc --cflags --ldflags` crash.c `bin/mruby-config --libs`
% ./a.out
zsh: segmentation fault (core dumped) ./a.out
```
After applying this patch, it will print exception object and exit normally.
The `mrb_protect()`, `mrb_ensure()` and `mrb_rescue_exceptions()` in `mrbgems/mruby-error` have been rewritten using `mrb_protect_raw()`.
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.
There are 3 levels of C++ exception handling:
* default - no C++ exception (use setjmp/longjmp)
* enable_cxx_exception (use C++ exceptions with C ABI)
* enable_cxx_abi (use C++ ABI including exceptions)
Yukihiro "Matz" Matsumoto