Feature #20273
closedDisable callcc when compiled with ASAN
Description
Currently, all of the callcc related tests in the Ruby test suite fail when Ruby is compiled with ASAN (CFLAGS="-fsanitize=address").
Unfortunately, I don't believe it's possible for calcc to be supported with ASAN at all. callcc is implemented by:
- When saving a continuation, we take a copy of C the stack, and a jmpbuf with
setjmp
. - When calling a continuation, we memcpy the C stack back from the saved copy (using
alloca
to move the current top-of-stack out of the way of this copying), and thenlongjmp
'ing back to the saved state
There are a few reasons this can't work with ASAN - some fixable, some not:
- The copying of the original stack when creating a continuation requires reading stack memory from outside the current function, which ASAN does not allow (and, likewise with copying the stack back). This can be fixed by using a custom memcpy implementation which has
__attribute__((no_sanitize("address")))
. - When we restore the original stack, we also need to restore the shadow-words for that memory range (which record the state of what memory is and is not valid according to ASAN). ASAN does not expose a pointer to the shadow stack to allow it to be copied like this, but this is in theory something which we could patch in LLVM if we wanted to.
- With ASAN, many local variables are not actually on the stack - rather, they're stored in a special "fake stack" (i think to enable detecting cases of stack-use-after-return). (I think) ASAN essentially malloc's memory for each function frame to hold these fake values, and frees them when the function returns. With callcc, some functions whose fake frames have already been freed might be re-entered, but the "fake stack" holding their local variables will have been freed. I don't believe there's a way to fix this that I can think of.
Therefore, I propose that:
- When cruby is compiled with
-fsanitize=address
in CFLAGS,Kernel#callcc
isrb_f_notimplement
. - That means
Kernel#respond_to?(:callcc) == false
, andKernel#callcc
raisesNotImplementedError
- Tests in the cruby test suite which use
callcc
checkrespond_to?(:callcc)
and skip themselves if so.
Since callcc is deprecated and meant only to be used for... um... "fun" things (https://bugs.ruby-lang.org/issues/10548), I think this is an acceptable tradeoff.
Updated by mame (Yusuke Endoh) 6 months ago
I think it makes sense basically. I would like to see details in PR. Do you already have a patch?
Updated by kjtsanaktsidis (KJ Tsanaktsidis) 6 months ago
What about something like this? https://github.com/ruby/ruby/pull/10012
This is the "maximal" way - it adds a new define RUBY_CALLCC_ENABLED
, which we set to on normally but off if asan is enabled. Then, all the callcc related code gets guarded by this macro (including the bits spread around in vm.c for example).
I can do something less invasive (like this? https://github.com/ruby/ruby/commit/b3500503478e81985ac8d95b3576135f9787bcf6) but that generates unused function warnings that would have to be suppressed (with some ignore_unused attributes or some such)
Updated by Anonymous 6 months ago
- Status changed from Open to Closed
Applied in changeset git|5621d794a2fa9293d1da489d6b0ee0e7c73c9128.
Disable callcc when ASAN is enabled
callcc's implementation is fundamentally incompatible with ASAN. Since
callcc is deprecated and almost never used, it's probably OK to disable
callcc when ruby is compiled with ASAN.
[Bug #20273]
Updated by kjtsanaktsidis (KJ Tsanaktsidis) 5 months ago
- Related to Misc #20387: Meta-ticket for ASAN support added