asm! support for the Xtensa architecture

[MabezDev]

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This implements the asm! support for Xtensa. We've been using this code for a few years in our fork and it's been working well. I finally found some time to clean it up a bit and start the upstreaming process. This should be one of the final PRs for Xtensa support on the Rust side (minus bug fixes of course). After this, we're mostly just waiting on the LLVM upstreaming which is going well. This PR doesn't cover all possible asm options for Xtensa, but the base ISA plus a few extras that are used in Espressif chips.

r? Amanieu

[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

[Amanieu]

This is also missing an update to the unstable book entry for asm_experimental_arch.

View changes since this review

[bors]

☔ The latest upstream changes (presumably #147645) made this pull request unmergeable. Please resolve the merge conflicts.

[MabezDev]

I've made most of the updates here (sorry for the delay!).

It turns out we'll need a patch that landed just after rust branched LLVM: https://github.com/rust-lang/llvm-project/tree/rustc/21.1-2025-08-01/llvm/lib/Target/Xtensa , otherwise the asm tests fail :(.

The good news is that we've since landed FP support in LLVM upstream too, so maybe the next time rust branches LLVM 21 (I guess 21.2?) we can rerun CI on this PR and it will be green.

[Dylan-DPC]

@MabezDev any updates on this and the pending review and test failures? thanks

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-log-analyzer]

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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To only update this specific test, also pass `--test-args check-cfg/target_feature.rs`

error: 1 errors occurred comparing output.
status: exit status: 0
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/check-cfg/target_feature.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/check-cfg/target_feature" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "--check-cfg=cfg()" "-Zcheck-cfg-all-expected"
stdout: none
--- stderr -------------------------------
warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
##[warning]  --> /checkout/tests/ui/check-cfg/target_feature.rs:16:10
   |
LL |     cfg!(target_feature = "_UNEXPECTED_VALUE");
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: expected values for `target_feature` are: `10e60`, `2e3`, `32s`, `3e3r1`, `3e3r2`, `3e3r3`, `3e7`, `7e10`, `a`, `aclass`, `addsubiw`, `adx`, `aes`, `allows-misaligned-mem-access`, `altivec`, `alu32`, `amx-avx512`, `amx-bf16`, `amx-complex`, `amx-fp16`, `amx-fp8`, `amx-int8`, `amx-movrs`, `amx-tf32`, `amx-tile`, `apxf`, `atomctl`, `atomics`, `audio`, `avx`, `avx10.1`, `avx10.2`, `avx2`, `avx512bf16`, `avx512bitalg`, `avx512bw`, `avx512cd`, `avx512dq`, `avx512f`, `avx512fp16`, `avx512ifma`, `avx512vbmi`, `avx512vbmi2`, `avx512vl`, `avx512vnni`, `avx512vp2intersect`, `avx512vpopcntdq`, `avxifma`, `avxneconvert`, `avxvnni`, `avxvnniint16`, `avxvnniint8`, `b`, `backchain`, `bf16`, `bmi1`, `bmi2`, `bool`, `break`, `bti`, `bulk-memory`, `c`, `cache`, `cmpxchg16b`, `concurrent-functions`, `coprocessor`, `crc`, `crt-static`, `cssc`, `d`, `d32`, `debug`, `deflate-conversion`, `dit`, `div32`, `doloop`, `dotprod`, `dpb`, `dpb2`, `dsp`, `dsp1e2`, `dspe60`, `e`, `e1`, `e2`, `ecv`, `edsp`, `eijmpcall`, `elpm`, `elpmx`, `elrw`, `enhanced-sort`, `ermsb`, `exception`, `exception-handling`, `extended-const`, `extendedl32r`, `f`, `f16c`, `f32mm`, `f64mm`, `faminmax`, `fcma`, `fdivdu`, `fhm`, `flagm`, `flagm2`, `float1e2`, `float1e3`, `float3e4`, `float7e60`, `floate1`, `fma`, `fma4`, `fp`, `fp-armv8`, `fp16`, `fp64`, `fp8`, `fp8dot2`, `fp8dot4`, `fp8fma`, `fpregs`, `fpuv2_df`, `fpuv2_sf`, `fpuv3_df`, `fpuv3_hf`, `fpuv3_hi`, `fpuv3_sf`, `frecipe`, `frintts`, `fxsr`, `gc`, `gfni`, `guarded-storage`, `hard-float`, `hard-float-abi`, `hard-tp`, `hbc`, `high-registers`, `high-word`, `highpriinterrupts`, `hvx`, `hvx-ieee-fp`, `hvx-length128b`, `hvx-length64b`, `hvx-qfloat`, `hvxv60`, `hvxv62`, `hvxv65`, `hvxv66`, `hvxv67`, `hvxv68`, `hvxv69`, `hvxv71`, `hvxv73`, `hvxv75`, `hvxv79`, `hwdiv`, `i8mm`, `ijmpcall`, `interrupt`, `isa-68000`, `isa-68010`, `isa-68020`, `isa-68030`, `isa-68040`, `isa-68060`, `isa-68881`, `isa-68882`, `jmpcall`, `jsconv`, `kl`, `lahfsahf`, `lam-bh`, `lamcas`, `lasx`, `lbt`, `ld-seq-sa`, `leoncasa`, `loop`, `lor`, `lowbytefirst`, `lpm`, `lpmx`, `lse`, `lse128`, `lse2`, `lsx`, `lut`, `lvz`, `lzcnt`, `m`, `mac16`, `mclass`, `memctl`, `message-security-assist-extension12`, `message-security-assist-extension3`, `message-security-assist-extension4`, `message-security-assist-extension5`, `message-security-assist-extension8`, `message-security-assist-extension9`, `miscellaneous-extensions-2`, `miscellaneous-extensions-3`, `miscellaneous-extensions-4`, `miscsr`, `mops`, `movbe`, `movrs`, `movw`, `mp`, `mp1e2`, `msa`, `msync`, `mte`, `mul`, `mul32`, `mul32high`, `multivalue`, `mutable-globals`, `neon`, `nnp-assist`, `nontrapping-fptoint`, `nsa`, `nvic`, `outline-atomics`, `paca`, `pacg`, `pan`, `partword-atomics`, `pauth-lr`, `pclmulqdq`, `pmuv3`, `popcnt`, `power10-vector`, `power8-altivec`, `power8-crypto`, `power8-vector`, `power9-altivec`, `power9-vector`, `prfchw`, `prid`, `ptx70`, `ptx71`, `ptx72`, `ptx73`, `ptx74`, `ptx75`, `ptx76`, `ptx77`, `ptx78`, `ptx80`, `ptx81`, `ptx82`, `ptx83`, `ptx84`, `ptx85`, `ptx86`, `ptx87`, `quadword-atomics`, `rand`, `ras`, `rclass`, `rcpc`, `rcpc2`, `rcpc3`, `rdm`, `rdrand`, `rdseed`, `reference-types`, `regprotect`, `relax`, `relaxed-simd`, `rmw`, `rtm`, `rva23u64`, `rvector`, `s32c1i`, `sb`, `scq`, `sext`, `sha`, `sha2`, `sha3`, `sha512`, `sign-ext`, `simd128`, `sm3`, `sm4`, `sm_100`, `sm_100a`, `sm_101`, `sm_101a`, `sm_120`, `sm_120a`, `sm_70`, `sm_72`, `sm_75`, `sm_80`, `sm_86`, `sm_87`, `sm_89`, `sm_90`, `sm_90a`, `sme`, `sme-b16b16`, `sme-f16f16`, `sme-f64f64`, `sme-f8f16`, `sme-f8f32`, `sme-fa64`, `sme-i16i64`, `sme-lutv2`, `sme2`, `sme2p1`, `soft-float`, `spe`, `spm`, `spmx`, `ssbs`, `sse`, `sse2`, `sse3`, `sse4.1`, `sse4.2`, `sse4a`, `ssse3`, `ssve-fp8dot2`, `ssve-fp8dot4`, `ssve-fp8fma`, `supm`, `sve`, `sve-b16b16`, `sve2`, `sve2-aes`, `sve2-bitperm`, `sve2-sha3`, `sve2-sm4`, `sve2p1`, `tail-call`, `tbm`, `threadptr`, `thumb-mode`, `thumb2`, `timerint`, `tinyencoding`, `tme`, `transactional-execution`, `trust`, `trustzone`, `ual`, `unaligned-scalar-mem`, `unaligned-vector-mem`, `v`, `v5te`, `v6`, `v60`, `v62`, `v65`, `v66`, `v67`, `v68`, `v69`, `v6k`, `v6t2`, `v7`, `v71`, `v73`, `v75`, `v79`, `v8`, `v8.1a`, `v8.2a`, `v8.3a`, `v8.4a`, `v8.5a`, `v8.6a`, `v8.7a`, `v8.8a`, `v8.9a`, `v8plus`, `v9`, `v9.1a`, `v9.2a`, `v9.3a`, `v9.4a`, `v9.5a`, `v9a`, `vaes`, `vdsp2e60f`, `vdspv1`, `vdspv2`, `vector`, `vector-enhancements-1`, `vector-enhancements-2`, `vector-enhancements-3`, `vector-packed-decimal`, `vector-packed-decimal-enhancement`, `vector-packed-decimal-enhancement-2`, `vector-packed-decimal-enhancement-3`, `vfp2`, `vfp3`, `vfp4`, `vh`, `virt`, `virtualization`, `vpclmulqdq`, `vsx`, `wfxt`, `wide-arithmetic`, `widekl`, `windowed`, `x87`, `xop`, `xsave`, `xsavec`, `xsaveopt`, `xsaves`, `za128rs`, `za64rs`, `zaamo`, `zabha`, `zacas`, `zalrsc`, `zama16b`, `zawrs`, `zba`, `zbb`, `zbc`, `zbkb`, `zbkc`, `zbkx`, `zbs`, `zca`, `zcb`, `zcmop`, `zdinx`, `zfa`, `zfbfmin`, `zfh`, `zfhmin`, `zfinx`, `zhinx`, `zhinxmin`, `zic64b`, `zicbom`, `zicbop`, `zicboz`, `ziccamoa`, `ziccif`, `zicclsm`, `ziccrse`, `zicntr`, `zicond`, `zicsr`, `zifencei`, `zihintntl`, `zihintpause`, `zihpm`, `zimop`, `zk`, `zkn`, `zknd`, `zkne`, `zkne_or_zknd`, `zknh`, `zkr`, `zks`, `zksed`, `zksh`, `zkt`, `zreg`, `ztso`, `zvbb`, `zvbc`, `zve32f`, `zve32x`, `zve64d`, `zve64f`, `zve64x`, `zvfbfmin`, `zvfbfwma`, `zvfh`, `zvfhmin`, `zvkb`, `zvkg`, `zvkn`, `zvknc`, `zvkned`, `zvkng`, `zvknha`, `zvknhb`, `zvks`, `zvksc`, `zvksed`, `zvksg`, `zvksh`, `zvkt`, `zvl1024b`, `zvl128b`, `zvl16384b`, `zvl2048b`, `zvl256b`, `zvl32768b`, `zvl32b`, `zvl4096b`, `zvl512b`, `zvl64b`, `zvl65536b`, and `zvl8192b`
   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
   = note: `#[warn(unexpected_cfgs)]` on by default

warning: 1 warning emitted
------------------------------------------