Ensure the VM is alive before accessing objspace in C API (Feature #19627) #7783
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nobu
requested changes
May 3, 2023
gc.c
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| ({ \ | ||
| rb_vm_t *rb_objspace_ptr_vm = GET_VM(); \ | ||
| (UNLIKELY(rb_objspace_ptr_vm == NULL)) ? NULL : ((rb_objspace_ptr_vm)->objspace); \ | ||
| }) |
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Statement expression is a gcc extension.
byroot
reviewed
May 3, 2023
gc.c
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| @@ -10914,15 +10919,17 @@ rb_gc_start(void) | |||
| void | |||
| rb_gc(void) | |||
| { | |||
| rb_objspace_t *objspace = &rb_objspace; | |||
| rb_objspace_t *objspace = rb_objspace_ptr(); | |||
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Rather than a rb_objspace_ptr macro, wouldn't it be more convenient to implement some kind of EARLY_RETURN_IF_SHUTTING_DOWN kind of help macro?
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Just an idea 😜
#define unless_objspace(objspace) \
rb_objspace_t *objspace; \
rb_vm_t *rb_objspace_ptr_vm = GET_VM(); \
if (rb_objspace_ptr_vm) objspace = rb_objspace_ptr_vm->objspace; \
else /* return; or objspace will be warned uninitialized */
unless_objspace(objspace) {return;}
// or
unless_objspace(objspace) {return FALSE;}There was a problem hiding this comment.
I tried out the early return approach, but doing it right involved some do while (0) trickery, and I couldn’t quite get it to properly return default values.
This approach seemed simpler to implement and easier to understand, but happy to try another approach. unless_objspace seems good, I’ll give it a whirl.
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Implemented in 77ad19c
byroot
reviewed
May 3, 2023
Co-authored-by: Jean Boussier <jean.boussier@gmail.com>
nobu
approved these changes
May 4, 2023
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It is not possible to ensure the Ruby VM is accessible in certain scenarios, such as thread local destructors and async signal handlers.
Previously, it was possible to workaround this by probing the hidden
ruby_current_vm_ptrsymbol. But as of #7459, those symbols are no longer visible.To remedy this, this patch adds some null checks when accessing
objspaceto eliminate known safety issues in the public C API (rb_during_gc,rb_gcandrb_gc_adjust_memory_usage).prior art: #7663
issue tracker: https://bugs.ruby-lang.org/issues/19627