[ruby-core:113488] [Ruby master Bug#19635] errno may be overwritten by rb_sprintf if it triggers GC

Issue #19635 has been updated by nobu (Nobuyoshi Nakada).


Thank you, I missed it.
Please update the dependency in common.mk too.

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Bug #19635: errno may be overwritten by rb_sprintf if it triggers GC
https://bugs.ruby-lang.org/issues/19635#change-103074

* Author: wks (Kunshan Wang)
* Status: Closed
* Priority: Normal
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
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Here is an excerpt in the `trap` function in `signal.c`

``` c
        oldfunc = ruby_signal(sig, func);
        if (oldfunc == SIG_ERR) rb_sys_fail_str(rb_signo2signm(sig));
```

`ruby_signal` tries to register a signal handling function.  If it fails, it returns `SIG_ERR`, and `errno` is set to by `sigaction` to indicate the error.

However, the snippet above calls `rb_signo2signm(sig)` before calling `rb_sys_fail_str`.  `rb_signo2signm` allocates a Ruby heap object using `rb_sprintf`.  The problem is, **if this `rb_sprintf` triggers GC**, the garbage collector may perform may complex operations, including executing `obj_free`, calling `mmap` to allocate more memory from the OS, etc.  They **may overwrite the `errno`**.

So if GC is triggered in the very unfortunate time, the caller of the `trap` function will receive an exception, but with the wrong reason.  This may cause some tests, such as the `test_trap_uncatchable_#{sig}` test cases in `test_signal.rb`, to fail.

There are similar use cases in `hash.c`, for example:

```c
        if (ret) rb_sys_fail_str(rb_sprintf("setenv(%s)", name));
```

The good practice is always loading from `errno` immediately after calling functions that may set `errno`, such as `sigaction` and `setenv`.



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