Failed to build on armv7 musl target on Alpine Linux

[messense]

https://gitlab.alpinelinux.org/messense/aports/-/jobs/853878

rustc version information:

$ rustc -vV
rustc 1.64.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: armv7-alpine-linux-musleabihf
release: 1.64.0
LLVM version: 14.0.6

error message:

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:13:9
   |
13 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:25:9
   |
25 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:40:9
   |
40 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:51:9
   |
51 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:66:9
   |
66 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:83:9
   |
83 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:101:9
    |
101 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:120:9
    |
120 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e[596](https://gitlab.alpinelinux.org/messense/aports/-/jobs/853878#L596)3aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:140:9
    |
140 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:161:9
    |
161 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:183:9
    |
183 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:206:9
    |
206 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:230:9
    |
230 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> /home/buildozer/.cargo/registry/src/github.com-1285ae84e5963aae/rustix-0.35.10/src/backend/linux_raw/arch/inline/arm.rs:255:9
    |
255 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^
   Compiling console v0.15.1
   Compiling rand_core v0.6.4
   Compiling uuid v0.8.2
   Compiling time v0.3.14
   Compiling charset v0.1.3
   Compiling addr2line v0.17.0
   Compiling dirs v4.0.0
   Compiling nb-connect v1.2.0
   Compiling matchers v0.1.0
   Compiling num-complex v0.4.2
   Compiling url v2.3.1
   Compiling parking_lot v0.12.1
   Compiling tar v0.4.38
   Compiling digest v0.9.0
   Compiling crypto-mac v0.11.1
   Compiling block-buffer v0.10.3
error: could not compile `rustix` due to 14 previous errors
warning: build failed, waiting for other jobs to finish...

[messense]

It seems that the armv7-alpine-linux-musleabihf target enabled thumb-mode feature thus r7 is the frame pointer.

• https://gitlab.alpinelinux.org/alpine/aports/-/blob/master/community/rust/alpine-target.patch#L57
• https://github.com/rust-lang/rust/blob/cd4d9d934fd3bc1b6a0b0fcb3548a1b26fc53c9d/compiler/rustc_target/src/asm/arm.rs#L67-L69
• https://github.com/rust-lang/rust/blob/cd4d9d934fd3bc1b6a0b0fcb3548a1b26fc53c9d/compiler/rustc_target/src/asm/arm.rs#L94-L95

[sunfishcode]

Thanks for the report! I've started working on a fix in #416.

[sunfishcode]

I can't find any upstream Rust Linux arm targets that enable thumb-mode which hit this. Would you be able to test whether #416 fixes the problem?

[messense]

RUSTFLAGS="-C target-feature=+thumb-mode" cargo build --target armv7-unknown-linux-musleabihf
   Compiling bitflags v1.3.2
   Compiling linux-raw-sys v0.0.46
   Compiling libc v0.2.133
   Compiling io-lifetimes v1.0.0-rc1
   Compiling rustix v0.36.0-rc2 (/Users/messense/Projects/rustix)
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> src/backend/linux_raw/arch/inline/arm.rs:13:9
   |
13 |         in("r7") nr.to_asm(),

RUSTFLAGS="-C target-feature=+thumb-mode" still gives me the same error.

docker run --rm -it --platform linux/arm/v7 alpine:edge
/ # uname -a
Linux 91928fdcd8a2 5.15.0-47-generic #51-Ubuntu SMP Fri Aug 12 08:18:32 UTC 2022 armv7l Linux
/ # apk add git cargo
/ # RUSTC_BOOTSTRAP=1 rustc -Zunstable-options --print target-spec-json
{
  "abi": "eabihf",
  "arch": "arm",
  "crt-static-respected": true,
  "data-layout": "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64",
  "dynamic-linking": true,
  "env": "musl",
  "features": "+v7,+vfp3,-d32,+thumb-mode,+thumb2",
  "has-rpath": true,
  "has-thread-local": true,
  "is-builtin": true,
  "llvm-target": "armv7-alpine-linux-musleabihf",
  "max-atomic-width": 64,
  "need-rpath": true,
  "os": "linux",
  "position-independent-executables": true,
  "relro-level": "full",
  "static-position-independent-executables": true,
  "target-family": [
    "unix"
  ],
  "target-mcount": "\u0001mcount",
  "target-pointer-width": "32",
  "vendor": "alpine"
}
/ # cd
~ # git clone https://github.com/bytecodealliance/rustix.git
Cloning into 'rustix'...
remote: Enumerating objects: 13387, done.
remote: Counting objects: 100% (80/80), done.
remote: Compressing objects: 100% (71/71), done.
remote: Total 13387 (delta 29), reused 24 (delta 9), pack-reused 13307
Receiving objects: 100% (13387/13387), 2.65 MiB | 9.56 MiB/s, done.
Resolving deltas: 100% (9323/9323), done.
~/rustix # cargo build --features=all-apis
    Updating crates.io index
  Downloaded itoa v1.0.3
  Downloaded bitflags v1.3.2
  Downloaded once_cell v1.15.0
  Downloaded libc v0.2.133
  Downloaded linux-raw-sys v0.0.46
  Downloaded io-lifetimes v1.0.0-rc1
  Downloaded 6 crates (1.5 MB) in 2.53s
   Compiling io-lifetimes v1.0.0-rc1
   Compiling libc v0.2.133
   Compiling rustix v0.36.0-rc2 (/root/rustix)
   Compiling bitflags v1.3.2
   Compiling once_cell v1.15.0
   Compiling itoa v1.0.3
   Compiling linux-raw-sys v0.0.46
error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> src/backend/linux_raw/arch/inline/arm.rs:13:9
   |
13 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> src/backend/linux_raw/arch/inline/arm.rs:25:9
   |
25 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> src/backend/linux_raw/arch/inline/arm.rs:40:9
   |
40 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> src/backend/linux_raw/arch/inline/arm.rs:51:9
   |
51 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> src/backend/linux_raw/arch/inline/arm.rs:66:9
   |
66 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
  --> src/backend/linux_raw/arch/inline/arm.rs:83:9
   |
83 |         in("r7") nr.to_asm(),
   |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:101:9
    |
101 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:120:9
    |
120 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:140:9
    |
140 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:161:9
    |
161 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:183:9
    |
183 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:206:9
    |
206 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:230:9
    |
230 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: cannot use register `r7`: the frame pointer (r7) cannot be used as an operand for inline asm
   --> src/backend/linux_raw/arch/inline/arm.rs:255:9
    |
255 |         in("r7") nr.to_asm(),
    |         ^^^^^^^^^^^^^^^^^^^^

error: could not compile `rustix` due to 14 previous errors

Also fails in Alpine Linux armv7l docker container.

[messense]

I just tried this code

#[cfg(not(target_arch = "arm"))]
compile_error!("not arm");

#[cfg(all(target_arch = "arm", target_feature = "thumb-mode"))]
compile_error!("arm thumb-mode");

#[cfg(all(target_arch = "arm", not(target_feature = "thumb-mode")))]
compile_error!("arm no thumb-mode");

• cargo build gives error: not arm because I'm on M2 Mac which is aarch64.
• cargo b --target armv7-unknown-linux-musleabihf gives error: arm no thumb-mode
• RUSTFLAGS="-C target-feature=+thumb-mode" cargo build --target armv7-unknown-linux-musleabihf also gives error: arm no thumb-mode

So it looks like the target-feature cfg isn't working.

[nibon7]

#[cfg(target_feature= "thumb-mode")] is false on alpine linux (rust 1.64.0)

[messense]

~ # rustc --print cfg
debug_assertions
panic="unwind"
target_arch="arm"
target_endian="little"
target_env="musl"
target_family="unix"
target_has_atomic="16"
target_has_atomic="32"
target_has_atomic="64"
target_has_atomic="8"
target_has_atomic="ptr"
target_os="linux"
target_pointer_width="32"
target_vendor="alpine"
unix

Indeed.

[nibon7]

~ # rustc --print cfg
debug_assertions
panic="unwind"
target_arch="arm"
target_endian="little"
target_env="musl"
target_family="unix"
target_has_atomic="16"
target_has_atomic="32"
target_has_atomic="64"
target_has_atomic="8"
target_has_atomic="ptr"
target_os="linux"
target_pointer_width="32"
target_vendor="alpine"
unix

no target_feature="thumb-mode" 🤣

[messense]

$ rustc --print cfg --target armv7-unknown-linux-musleabihf -C target-feature=+thumb-mode
debug_assertions
panic="unwind"
target_arch="arm"
target_endian="little"
target_env="musl"
target_family="unix"
target_feature="crt-static"
target_has_atomic="16"
target_has_atomic="32"
target_has_atomic="64"
target_has_atomic="8"
target_has_atomic="ptr"
target_os="linux"
target_pointer_width="32"
target_vendor="unknown"
unix

$ rustc +nightly --print cfg --target armv7-unknown-linux-musleabihf -C target-feature=+thumb-mode
debug_assertions
panic="unwind"
target_abi="eabihf"
target_arch="arm"
target_endian="little"
target_env="musl"
target_family="unix"
target_feature="aclass"
target_feature="crt-static"
target_feature="dsp"
target_feature="llvm14-builtins-abi"
target_feature="thumb-mode"
target_feature="thumb2"
target_feature="v5te"
target_feature="v6"
target_feature="v6k"
target_feature="v6t2"
target_feature="v7"
target_feature="vfp2"
target_has_atomic="16"
target_has_atomic="32"
target_has_atomic="64"
target_has_atomic="8"
target_has_atomic="ptr"
target_has_atomic_equal_alignment="16"
target_has_atomic_equal_alignment="32"
target_has_atomic_equal_alignment="64"
target_has_atomic_equal_alignment="8"
target_has_atomic_equal_alignment="ptr"
target_has_atomic_load_store="16"
target_has_atomic_load_store="32"
target_has_atomic_load_store="64"
target_has_atomic_load_store="8"
target_has_atomic_load_store="ptr"
target_os="linux"
target_pointer_width="32"
target_thread_local
target_vendor="unknown"
unix

Seems like it's working on nightly Rust, not on stable yet.

[messense]

I just tried this code

#[cfg(not(target_arch = "arm"))]
compile_error!("not arm");

#[cfg(all(target_arch = "arm", target_feature = "thumb-mode"))]
compile_error!("arm thumb-mode");

#[cfg(all(target_arch = "arm", not(target_feature = "thumb-mode")))]
compile_error!("arm no thumb-mode");

• cargo build gives error: not arm because I'm on M2 Mac which is aarch64.
• cargo b --target armv7-unknown-linux-musleabihf gives error: arm no thumb-mode
• RUSTFLAGS="-C target-feature=+thumb-mode" cargo build --target armv7-unknown-linux-musleabihf also gives error: arm no thumb-mode

So it looks like the target-feature cfg isn't working.

This also correctly outputs error: arm thumb-mode on nightly when running RUSTFLAGS="-C target-feature=+thumb-mode" cargo +nightly build --target armv7-unknown-linux-musleabihf.

[messense]

Related rust-lang/rust#83975 (comment)