Missing symbol in no_std application on panic (windows-msvc)

[bearmate]

A no_std application with the panic strategy set to abort and a panic_handler defined still needs the symbol "__CxxFrameHandler3" if a panic is invoked. The toolchain is nightly-x86_64-pc-windows-msvc.

A sample failing to compile due to this can be found at this repository. It contains a minimal implementation of a no_std binary for windows with stubs for the needed memory functions and the panic_handler.

#![no_std]
#![no_main]
#![feature(panic_handler)]

use core::panic::PanicInfo;

#[panic_handler]
fn handle_panic(_: &PanicInfo) -> ! {
    loop {}
}

#[no_mangle]
pub unsafe extern "C" fn memcpy(dest: *mut u8, _src: *const u8, _n: usize) -> *mut u8 {
    dest
}

#[no_mangle]
pub unsafe extern "C" fn memmove(dest: *mut u8, _src: *const u8, _n: usize) -> *mut u8 {
    dest
}

#[no_mangle]
pub unsafe extern "C" fn memset(mem: *mut u8, _val: i32, _n: usize) -> *mut u8 {
    mem
}

#[no_mangle]
pub unsafe extern "C" fn memcmp(_mem1: *const u8, _mem2: *const u8, _n: usize) -> i32 {
    0
}

#[no_mangle]
pub extern "C" fn mainCRTStartup() -> ! {
    main()
}

#[no_mangle]
pub extern "C" fn main() -> ! {
    panic!()
}

I expected the application to compile just fine, because a panic_handler is defined and the panic strategy is set to "abort".

Instead I get a linker error complaining about the missing symbol "__CxxFrameHandler3". This only occurs if panic! is called. If I instead just loop forever in the main function, the compiler will return no error and work just fine.

Meta

PS D:\prj\test\no-std-minimal> cargo build --verbose
   Compiling no-std-minimal v0.1.0 (file:///D:/prj/test/no-std-minimal)
     Running `rustc --crate-name no_std_minimal src\main.rs --crate-type bin --emit=dep-info,link -C panic=abort -C debuginfo=2 -C metadata=f00f98cc62ddcb51 -C extra-filename=-f00f98cc62ddcb51 --out-dir D:\prj\test\no-std-minimal\target\debug\deps -C incremental=D:\prj\test\no-std-minimal\target\debug\incremental -L dependency=D:\prj\test\no-std-minimal\target\debug\deps`
error: linking with `link.exe` failed: exit code: 1120
  |
  = note: "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Community\\VC\\Tools\\MSVC\\14.13.26128\\bin\\HostX64\\x64\\link.exe" "/NOLOGO" "/NXCOMPAT" "/LIBPATH:C:\\Users\\bruno\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib" "D:\\prj\\test\\no-std-minimal\\target\\debug\\deps\\no_std_minimal-f00f98cc62ddcb51.4kfg7hloiv5kxloy.rcgu.o" "/OUT:D:\\prj\\test\\no-std-minimal\\target\\debug\\deps\\no_std_minimal-f00f98cc62ddcb51.exe" "/OPT:REF,NOICF" "/DEBUG" "/NATVIS:C:\\Users\\bruno\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\intrinsic.natvis" "/NATVIS:C:\\Users\\bruno\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\liballoc.natvis" "/NATVIS:C:\\Users\\bruno\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\libcore.natvis" "/LIBPATH:D:\\prj\\test\\no-std-minimal\\target\\debug\\deps" "/LIBPATH:C:\\Users\\bruno\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib" "C:\\Users\\bruno\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcore-68a97103729b5fa4.rlib" "C:\\Users\\bruno\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcompiler_builtins-8c450e159daacabd.rlib"
  = note: Non-UTF-8 output: libcore-68a97103729b5fa4.rlib(core-68a97103729b5fa4.core.d33te014-cgu.15.rcgu.o) : error LNK2001: Nicht aufgel\xf6stes externes Symbol \"__CxxFrameHandler3\".\r\nD:\\prj\\test\\no-std-minimal\\target\\debug\\deps\\no_std_minimal-f00f98cc62ddcb51.exe : fatal error LNK1120: 1 nicht aufgel\xf6ste Externe\r\n

error: aborting due to previous error

error: Could not compile `no-std-minimal`.

Caused by:
  process didn't exit successfully: `rustc --crate-name no_std_minimal src\main.rs --crate-type bin --emit=dep-info,link -C panic=abort -C debuginfo=2 -C metadata=f00f98cc62ddcb51 -C extra-filename=-f00f98cc62ddcb51 --out-dir D:\prj\test\no-std-minimal\target\debug\deps -C incremental=D:\prj\test\no-std-minimal\target\debug\incremental -L dependency=D:\prj\test\no-std-minimal\target\debug\deps` (exit code: 1)

[Erzawenn]

I'm facing the same issue with stable version 1.36. I don't know if it is an issue in the documentation which doesn't state that on Windows, you have to link with CRT or in the crate panic_abort that doesn't define this symbole on msvc starget.

In src\librustc_codegen_llvm\context.rs, a different name is defined for rust_eh_personality:

       let llfn = match tcx.lang_items().eh_personality() {
            Some(def_id) if !wants_msvc_seh(self.sess()) => {
                resolve_and_get_fn(self, def_id, tcx.intern_substs(&[]))
            }
            _ => {
                let name = if wants_msvc_seh(self.sess()) {
                    "__CxxFrameHandler3"
                } else {
                    "rust_eh_personality"
                };
                let fty = self.type_variadic_func(&[], self.type_i32());
                self.declare_cfn(name, fty)
            }
        };

But, unfortunatly, in crate libpanic_abort, rust_eh_personality is inconditionnaly defined.

Two examples of code that compiles:

• with CRT linkage

#![cfg(target_os = "windows")]
#![no_std]
#![no_main]
#![windows_subsystem = "console"]

use core::panic::PanicInfo;

// required by no_std
#[panic_handler]
fn handle_panic(_info: &PanicInfo) -> ! {
    loop {}
}

// linkage to CRT library according to crt-static flag set in .cargo/config:
// [target.x86_64-pc-windows-msvc]
// rustflags = ["-C", "target-feature=+crt-static"]
#[cfg(target_feature = "crt-static")]
#[link(name = "libcmt")]
extern {}
#[cfg(not(target_feature = "crt-static"))]
#[link(name = "msvcrt")]
extern {}

// CRT is used, the entry point is main
#[no_mangle]
pub extern "C" fn main() -> i32 {
    panic!();
}

• with symbole __CxxFrameHandler3

#![cfg(target_os = "windows")]
#![no_std]
#![no_main]
#![windows_subsystem = "console"]

use core::panic::PanicInfo;

// required by no_std
#[panic_handler]
fn handle_panic(_info: &PanicInfo) -> ! {
    loop {}
}

#[no_mangle]
pub unsafe extern "C" fn memset(mem: *mut u8, _val: i32, _n: usize) -> *mut u8 {
    mem
}

#[no_mangle]
pub unsafe extern "C" fn memcpy(dest: *mut u8, _src: *const u8, _n: usize) -> *mut u8 {
    dest
}

#[no_mangle]
pub unsafe extern "C" fn memcmp(_mem1: *const u8, _mem2: *const u8, _n: usize) -> i32 {
    0
}

#[no_mangle]
pub extern "C" fn __CxxFrameHandler3() {
}

// no CRT and console subsystem => the entry point is mainCRTStartup
#[no_mangle]
pub extern "C" fn mainCRTStartup() -> ! {
    panic!();
}

[bearmate]

From the comments it looks like __CxxFrameHandler3 is used as the personality function on msvc to convince LLVM to use SEH instead of Dwarf exception handling, so it does not inject a dependency to _Unwind_Resume. Is this even necessary for panic=abort? Couldn't we keep rust_eh_personality on msvc if panic=abort and everything would work fine?

[Berrysoft]

Could we just forward to __CxxFrameHandler3 in rust_eh_personality, and remove the requirement of __CxxFrameHandler3 in context.rs? I'll try to do that later.

[rylev]

Going to close this as this no longer seems to be an issue. See here for more information.