f128 cmath functions broken in windows

[zinkkkk]

Under windows using #![feature(f128)] almost all of the f128 math functions cannot be compiled, it appears to be a linking error/missing symbols.

Normal math operations like add, sub, mul ect all compile and run fine but calling anything like .sin() or .gamma() or anything called under cmath will not compile. However, any of the math functions called as part of intrinsics do compile fine. This appears to be windows specific as the identical code compiles fine under wsl, both using latest rust nightly.

I have also tried using normal msvc linker link.exe and rust-lld.exe both with identical results, and also tested with gnu toolchain again with identical results.

#![feature(f128)]

fn main() {
    let a: f128 = 5.7;
    println!("f128 sin = {:#?}", (a.sin()));
}

PS C:\Users\levia\Documents\Code\f128stuff> cargo run --release
   Compiling f128stuff v0.1.0 (C:\Users\levia\Documents\Code\f128stuff)
error: linking with `rust-lld` failed: exit code: 1
  |
  = note: "rust-lld" "-flavor" "link" "/NOLOGO" "C:\\Users\\levia\\AppData\\Local\\Temp\\rustcEK3Fy2\\symbols.o" "C:\\Users\\levia\\Documents\\Code\\f128stuff\\target\\release\\deps\\f128stuff.f128stuff.6f36ac2c2723ffe0-cgu.0.rcgu.o" "C:\\Users\\levia\\Documents\\Code\\f128stuff\\target\\release\\deps\\f128stuff.9j8x1nkqyt711ce2p3mysxkj3.rcgu.o" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd-c09b6dac30a2ec7e.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libpanic_unwind-f2b3338f491e0297.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libwindows_targets-650a9189f256d76e.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librustc_demangle-7ce081cb32ea6b96.rlib" 
"C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd_detect-f80ba4624fd5706a.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libhashbrown-6fe121940227f580.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librustc_std_workspace_alloc-316118e870ffb802.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libunwind-af3779e04d2c5b3e.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcfg_if-d8b574f6478ea10a.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liballoc-8a746df5f193254d.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librustc_std_workspace_core-5a536bba43fbe272.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcore-45b7a05b67ddb8c6.rlib" "C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcompiler_builtins-c25bba97e86b102c.rlib" "kernel32.lib" "kernel32.lib" "advapi32.lib" "ntdll.lib" "userenv.lib" "ws2_32.lib" "dbghelp.lib" "/defaultlib:msvcrt" "/NXCOMPAT" "/OUT:C:\\Users\\levia\\Documents\\Code\\f128stuff\\target\\release\\deps\\f128stuff.exe" "/OPT:REF,ICF" "/DEBUG" "/PDBALTPATH:%_PDB%" "/NATVIS:C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\intrinsic.natvis" "/NATVIS:C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\liballoc.natvis" "/NATVIS:C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\libcore.natvis" "/NATVIS:C:\\Users\\levia\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\libstd.natvis"
  = note: rust-lld: error: undefined symbol: sinl␍
          >>> referenced by C:\Users\levia\Documents\Code\f128stuff\target\release\deps\f128stuff.f128stuff.6f36ac2c2723ffe0-cgu.0.rcgu.o:(f128stuff::main::ha078482b952c8e41)␍


error: could not compile `f128stuff` (bin "f128stuff") due to 1 previous error

but exact same code under wsl:

zink@baph:/mnt/c/Users/levia/Documents/Code/f128stuff$ cargo run --release
   Compiling f128stuff v0.1.0 (/mnt/c/Users/levia/Documents/Code/f128stuff)
    Finished `release` profile [optimized] target(s) in 0.64s
     Running `target/release/f128stuff`
f128 sin = 0xbffe19f37497ac7a1a58c25c354ac88a
zink@baph:/mnt/c/Users/levia/Documents/Code/f128stuff$

related to
#128417
#116909

[tgross35]

This is more or less expected for the time being. Windows, among other platforms, basically doesn't touch f128 so they don't provide cmath. There is a note about this in the docs, though it isn't very specific:

Note: f128 support is incomplete. Many platforms will not be able to link math functions. On x86 in particular, these functions do link but their results are always incorrect.

The resolution here is for us to add these to our libm and then make them available everywhere. It is in progress but this is something that will take a lot of time.

[tgross35]

If you want to experiment with this, -windows-gnu may have the required symbols or you may be able to build a C math library and link that. Note that even if linking succeeds that you will get the wrong results on x86 Windows, LLVM has a lowering bug where functions turn into the long double sinl functions rather than sinf128.

I am going to close this since there isn't really anything actionable, the required changes here are tracked in other places (but most of the updates will be in libm).