Issue w/ Bool - Invalid memory access (signal 11) at address 0x0

[lwakefield]

I've been chasing this error for a hot second, and have finally narrowed (reproducible, at least for me) it down to "pg"!

The wrinkle is, the crash only shows up when built with the --release flag, which of course has more obtuse debugging output...

From what I can tell so far, this only occurs when querying and casting for Bool. Though TBD if I can recreate with other data types...

So with:

require "pg"

conn = PG.connect("postgres://postgres@localhost:5432/postgres")
pp conn.query_one("select true", as: Bool)
conn.close

and

$ crystal run tmp/pg_crash.cr
true

but...

$ crystal run --release tmp/pg_crash.cr
Invalid memory access (signal 11) at address 0x0
[0x60031319c649] ?? +105566321624649 in /home/codespace/.cache/crystal/crystal-run-pg_crash.tmp
[0x60031319c600] ?? +105566321624576 in /home/codespace/.cache/crystal/crystal-run-pg_crash.tmp
[0x7afceeeea420] ?? +135226758964256 in /lib/x86_64-linux-gnu/libpthread.so.0
[0x6003131fd359] ?? +105566322021209 in /home/codespace/.cache/crystal/crystal-run-pg_crash.tmp
[0x600313168802] __crystal_main +60226 in /home/codespace/.cache/crystal/crystal-run-pg_crash.tmp
[0x60031316fc8b] main +59 in /home/codespace/.cache/crystal/crystal-run-pg_crash.tmp
[0x7afceec8f083] __libc_start_main +243 in /lib/x86_64-linux-gnu/libc.so.6
[0x600313159bfe] _start +46 in /home/codespace/.cache/crystal/crystal-run-pg_crash.tmp
[0x0] ???

Creating this issue in case it is obvious to others, others experience something similar, or others have pointers for me. But ideally I'm planning on chasing this down myself...

[lwakefield]

~Well... I found a "fix" but I'm not trying to work out why it works, because it feels very hacky...~

Edit - seems this doesn't consistently work, which is fine because I was definitely throwing spaghetti and seeing what stuck...

https://github.com/lwakefield/crystal-pg/commit/1012f8b4a91b1f0c7b941a3fca704ccf9b428bbe

      begin
-       yield @sized_io
+       r = yield @sized_io
+       r

[straight-shoota]

This smells like a bug in LLVM (or the Crystal compiler).

I can reproduce the invalid memory access only on Crystal built with LLVM 18, not with LLVM 17.

[lwakefield]

yes - I was coming to a conclusion that I was going to be out of my depth shortly... So that checks out!

@straight-shoota - do you have any tips to generate useful diagnostics? I'm planning on simply logging an issue over on https://github.com/crystal-lang/crystal with as much diagnostic information as possible (everything I posted here plus some versions of crystal/llvm/pg).

[straight-shoota]

Sounds good. I don't think much information about the environment is necessary because the issue clearly reproduces with LLVM 18 but not with LLVM 17:

The error reproduces with the latest 1.13.1 compiler built with LLVM 18:

$ crystal --version
Crystal 1.13.1 (2024-07-12)

LLVM: 18.1.8
Default target: x86_64-unknown-linux-gnu
$ crystal build bool.cr --release
$ ./bool
Invalid memory access (signal 11) at address 0x0
[0x55f506c614e9] ?? +94510868993257 in ./memory-llvm18
[0x55f506c614a0] ?? +94510868993184 in ./memory-llvm18
[0x7fbfda745520] ?? +140461980538144 in /lib/x86_64-linux-gnu/libc.so.6
[0x55f506cc1f6e] ?? +94510869389166 in ./memory-llvm18
[0x55f506c2d6d2] __crystal_main +60258 in ./memory-llvm18
[0x55f506c34b5b] main +59 in ./memory-llvm18
[0x7fbfda72cd90] ?? +140461980437904 in /lib/x86_64-linux-gnu/libc.so.6
[0x7fbfda72ce40] __libc_start_main +128 in /lib/x86_64-linux-gnu/libc.so.6
[0x55f506c1eaa5] _start +37 in ./memory-llvm18
[0x0] ??

It does not reproduce with the latest 1.13.1 compiler built with LLVM 17:

$ crystal
Crystal 1.13.1 (2024-07-12)

LLVM: 17.0.6
Default target: x86_64-pc-linux-gnu
$ crystal build bool.cr  --release
Using compiled compiler at /crystal/.build/crystal
$ ./bool
true

[straight-shoota]

I created https://github.com/crystal-lang/crystal/issues/14898 to track this issue in the Crystal repo.

[will]

Thanks @straight-shoota for opening it there, and nice find @lwakefield! I'm going to close this one here since it seems like the new issue in crystal-lang/crystal is a better spot. But if anyone disagrees let me know and we can reopen this one.

[compumike]

Just wanted to say thanks to everyone in this discussion! :heart: Great job tracking it down to such a simple example @lwakefield -- this appears to have fixed our issue too: Invalid memory access (signal 11) on 1.13.1, not present on 1.12.2?

[zw963]

Don't know if this issue is related to https://github.com/crystal-lang/crystal-sqlite3/issues/96, but anyway, will try later.

[straight-shoota]

If it reproduces with a Crystal compiler <= 1.13.1 that uses LLVM 18, but not when using LLVM < 18, it's probably the same issue. You may also check against Crystal nightly where the bug is fixed and it should work regardless of LLVM version.

[zw963]

I can still reproduce my issue on Crystal 1.13.2, as following screenshot.