force-unwind-tables has no effect on windows

[stevemk14ebr]

Hello, i'm building a no_std rust driver for windows and the unwind tables are not being generated in release mode. This is a large issue for be because i'm interacting with a kernel interfaces that requires the unwind_table entry for a specific function. Here is the issue in detail: rust-lang/backtrace-rs#397 (comment)

I'd expect that even though i've set the panic=abort mode that unwind tables are generated, and especially with the force-unwind-tables flag set to yes. I only need a specific function to have an unwind entry, so perhaps a #[unwind_entry] function attribute could make sense to introduce? The panic behavior should be separate from what binary tables are generated, they are separate concerns...

[stevemk14ebr]

It seems sometimes it does include the table but sometimes not. A rebuild fixed it in at least one case.

[Enselic]

Triage: Is this still a problem? If yes, can you provide detailed step-by-step instructions on how to reproduce please? Thanks! (That a rebuild fixed it make me suspect this is not a rustc bug.)

[Enselic]

Triage: I'm assuming this is not a problem any longer. Closing as obsolete.

[stevemk14ebr]

I wouldn't assume that but sure

#143613

3 months ago by you may have fixed 🤷🏻‍♂️

[Enselic]

If I wrongly closed this, I apologize and will happily re-open if needed. But can you still reproduce the problem? If yes, how exactly?

My PR you link to only changes Linux targets, so it can't have changed anything for Windows.

[stevemk14ebr]

I've confirmed it's still an issue on nightly. Do the following to repro:

# clone repro branch
git clone -b repro_unwind_nogen https://github.com/mandiant/STrace.git

# build test wasm script embedded into driver
cd .\STrace\Rust\WasmScript\
cargo build
cargo build --release

# build driver
cd .\STrace\Rust\Driver\
cargo build
cargo build --release

This will generate a windows driver under target\x86_64-pc-windows-msvc\ in the debug or release folder named STrace.dll (it's actually a .sys but doesn't matter). Open the DLL in IDA (can use freeware if you want), select yes to load the PDB, and search for function TraceAccessMemory. Scroll to the function name in the disassembly graph view and then press X on this name to lookup cross references. In the XRef view for the debug build you will see a RUNTIME_FUNCTION entry for the unwind info, but in the release build you will see that there is no RUNTIME_FUNCTION entry because the unwind info was not generated.

Debug:

Release:

The branch I made is configured to reproduce already but the config was also documented at rust-lang/backtrace-rs#397 (comment) in detail. On the master branch I have a slightly different config that I don't think runs into this issue, mostly because I set LTO to thin I think, but it's been a while I don't remember if master works or not with unwind generation.

[Enselic]

Thanks, let's reopen. If you can minimize the reproducer, the chance of someone looking into this and fixing it dramatically increases.