Fail to generate bindings for functions with calling convention "aapcs-vfp" for armv7a

[andersrein]

Input C/C++ Header

__attribute__((pcs("aapcs-vfp"))) float square_root(float input);

Bindgen Invocation

    bindgen::Builder::default()
        .header("fail.h")
        .whitelist_function("square_root")
        .generate()
        .expect("Failed to generate bindings")
        .write_to_file(out_path.join("square_root.rs"))
        .expect("Failed to WRITE bindings");

NOTE! The bug only occurs when cargo is invoked with the --target armv7-linux-androideabi flag because aapcs-vfp is ignored for all other platforms.

Actual Results

   Compiling bindgen_fail v0.1.0 (/home/are/source/bindgen_fail)
error: failed to run custom build command for `bindgen_fail v0.1.0 (/home/are/source/bindgen_fail)`

Caused by:
  process didn't exit successfully: `/home/are/source/bindgen_fail/target/debug/build/bindgen_fail-d45863190521fcb5/build-script-build` (exit code: 101)
--- stdout
cargo:warning=couldn't execute `llvm-config --prefix` (error: No such file or directory (os error 2))
cargo:warning=set the LLVM_CONFIG_PATH environment variable to a valid `llvm-config` executable

--- stderr
thread 'main' panicked at 'Invalid or unknown abi 7 for function "square_root" (Function { name: "square_root", mangled_name: Some("square_root"), signature: TypeId(ItemId(1)), comment: None, kind: Function, linkage: External })', /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:3415:17
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   4: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:474
   5: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:381
   6: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:336
   7: <bindgen::ir::function::Function as bindgen::codegen::CodeGenerator>::codegen
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:3415
   8: <bindgen::ir::item::Item as bindgen::codegen::CodeGenerator>::codegen
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:364
   9: <bindgen::ir::module::Module as bindgen::codegen::CodeGenerator>::codegen::{{closure}}
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:392
  10: <bindgen::ir::module::Module as bindgen::codegen::CodeGenerator>::codegen
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:422
  11: <bindgen::ir::item::Item as bindgen::codegen::CodeGenerator>::codegen
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:361
  12: bindgen::codegen::codegen::{{closure}}
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:3587
  13: bindgen::ir::context::BindgenContext::gen
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/ir/context.rs:1233
  14: bindgen::codegen::codegen
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/codegen/mod.rs:3564
  15: bindgen::Bindings::generate
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/lib.rs:1843
  16: bindgen::Builder::generate
             at /home/are/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.51.0/src/lib.rs:1228
  17: build_script_build::main
             at ./build.rs:8
  18: std::rt::lang_start::{{closure}}
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/libstd/rt.rs:64
  19: std::panicking::try::do_call
             at src/libstd/rt.rs:49
             at src/libstd/panicking.rs:293
  20: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:85
  21: std::rt::lang_start_internal
             at src/libstd/panicking.rs:272
             at src/libstd/panic.rs:394
             at src/libstd/rt.rs:48
  22: std::rt::lang_start
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/libstd/rt.rs:64
  23: main
  24: __libc_start_main
  25: _start

Expected Results

Expect it to be able to generate rust bindings of this simple header.

[emilio]

Does Rust support this ABI?

[andersrein]

Honestly I don't know. I've never heard of it. I just encountered it while trying to create rust bindings from the vulkan headers in the Android NDK. Rust does support armv7-linux-androideabi, however I am not sure about this exact calling convention. Somewhat difficult to find any documentation about what it is or whether or not rust supports it. I found this post which talks about adding support for aapcs-vfp: rust-lang/rust#37810

[emilio]

Oh so it looks like extern "aapcs" fn is a thing... But not extern "aapcs-vfp" unfortunately:

https://github.com/rust-lang/rust/blob/5421d94960018235654c7fb39aa1c502a3564621/src/librustc_target/abi/call/mod.rs#L503

You need to add extern "aapcs-vfp" fn support to rustc (should be trivial by looking at related patches there). Once that's done, adding support to bindgen is trivial. Something like this should do:

diff --git a/src/ir/function.rs b/src/ir/function.rs
index b8af9213..de3c3e8b 100644
--- a/src/ir/function.rs
+++ b/src/ir/function.rs
@@ -175,6 +175,8 @@ pub enum Abi {
     ThisCall,
     /// The "aapcs" ABI.
     Aapcs,
+    /// The "aapcs-vfp" ABI.
+    AapcsVfp,
     /// The "win64" ABI.
     Win64,
     /// An unknown or invalid ABI.
@@ -199,6 +201,7 @@ impl quote::ToTokens for Abi {
             Abi::Fastcall => quote! { "fastcall" },
             Abi::ThisCall => quote! { "thiscall" },
             Abi::Aapcs => quote! { "aapcs" },
+            Abi::AapcsVfp => quote! { "aapcs-vfp" },
             Abi::Win64 => quote! { "win64" },
             Abi::Unknown(cc) => panic!(
                 "Cannot turn unknown calling convention to tokens: {:?}",
@@ -237,6 +240,7 @@ fn get_abi(cc: CXCallingConv) -> Abi {
         CXCallingConv_X86FastCall => Abi::Fastcall,
         CXCallingConv_X86ThisCall => Abi::ThisCall,
         CXCallingConv_AAPCS => Abi::Aapcs,
+        CXCallingConv_AAPCS_VFP => Abi::AapcsVfp,
         CXCallingConv_X86_64Win64 => Abi::Win64,
         other => Abi::Unknown(other),
     }

But making bindgen generate the extern fn without support from rust is kinda useless.

[pvdrz]

Closing this as aapcs-vfp support has not been added to rustc yet. Feel free to reopen it if that changes.