AEABI division function linking problems (again)

[Lokathor]

I got a bug report yesterday that the gba crate no longer builds because of linking errors (rust-console/gba#187).

error: linking with `rust-lld` failed: exit code: 1
  |
  = note: "rust-lld" "-flavor" "gnu" "C:\\Users\\Daniel\\AppData\\Local\\Temp\\rustccI5P5G\\symbols.o" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\examples\\hello-472b02b74d42dc56.hello.ff7e989594f6dafe-cgu.0.rcgu.o" "--as-needed" "-L" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps" "-L" "D:\\dev\\gba\\target\\debug\\deps" "-L" "C:\\Users\\Daniel\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\thumbv4t-none-eabi\\lib" "-Bstatic" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps\\libgba-9a437158f6d53742.rlib" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps\\libbracer-de8a5334b1c7d053.rlib" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps\\libbitfrob-c6a9cbfb626642c0.rlib" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps\\libvoladdress-6c15bc02bfc75894.rlib" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps\\librustc_std_workspace_core-a7ec4ea53facd032.rlib" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps\\libcore-71be2443f3a85b43.rlib" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\deps\\libcompiler_builtins-d2b4ad49f4a33cb8.rlib" "-Bdynamic" "--eh-frame-hdr" "-z" "noexecstack" "-L" "C:\\Users\\Daniel\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\thumbv4t-none-eabi\\lib" "-o" "D:\\dev\\gba\\target\\thumbv4t-none-eabi\\debug\\examples\\hello-472b02b74d42dc56" "--gc-sections" "-O1" "-Tlinker_scripts/mono_boot.ld"
  = note: rust-lld: error: duplicate symbol: __aeabi_uidiv
          >>> defined at asm_runtime.rs:206 (src\asm_runtime.rs:206)
          >>>            gba-9a437158f6d53742.gba.d4abc47cdc4ad47-cgu.0.rcgu.o:(__aeabi_uidiv) in archive D:\dev\gba\target\thumbv4t-none-eabi\debug\deps\libgba-9a437158f6d53742.rlib
          >>> defined at macros.rs:372 (src\macros.rs:372)
          >>>            compiler_builtins-d2b4ad49f4a33cb8.compiler_builtins.ee71fd72058c181a-cgu.0.rcgu.o:(.text.__aeabi_uidiv+0x1) in archive D:\dev\gba\target\thumbv4t-none-eabi\debug\deps\libcompiler_builtins-d2b4ad49f4a33cb8.rlib

          rust-lld: error: duplicate symbol: __aeabi_idiv
          >>> defined at asm_runtime.rs:248 (src\asm_runtime.rs:248)
          >>>            gba-9a437158f6d53742.gba.d4abc47cdc4ad47-cgu.0.rcgu.o:(__aeabi_idiv) in archive D:\dev\gba\target\thumbv4t-none-eabi\debug\deps\libgba-9a437158f6d53742.rlib
          >>> defined at macros.rs:372 (src\macros.rs:372)
          >>>            compiler_builtins-d2b4ad49f4a33cb8.compiler_builtins.ee71fd72058c181a-cgu.0.rcgu.o:(.text.__aeabi_idiv+0x1) in archive D:\dev\gba\target\thumbv4t-none-eabi\debug\deps\libcompiler_builtins-d2b4ad49f4a33cb8.rlib


error: could not compile `gba` (example "hello") due to previous error

And, indeed, if I comment the division functions from the gba crate then it does build.

In #478 the division functions were made to be weak-link, so this seems to be a regression of some form.

Looking into the recent PRs, #526 may have done something weird? I'm not familiar enough with the macros to say for sure, but the person who reported the bug to the gba crate said that the Nightly from May 1 didn't have the problem, and now there is the problem, so the dates would seem to line up.

[Amanieu]

Can you try building with -Z build-std-features=compiler-builtins-weak-intrinsics? It should force all intrinsics to be built as weak functions.

[Lokathor]

I updated the project's .cargo/config.toml "unstable" section:

[unstable]
build-std = ["core"]
build-std-features = ["compiler-builtins-weak-intrinsics"]

and it does work now on Nightly-2023-07-11 (compiler_builtins-0.1.95)

I guess my question is why this was moved behind a feature flag?