sparc64 has incorrect ABI for struct containing f64 and f32

[erikdesjardins]

I tried this code:

// with --target=sparc64-unknown-linux-gnu

#[repr(C)]
pub struct DoubleFloat {
    f: f64,
    g: f32,
}

#[no_mangle]
pub extern "C" fn foo(x: DoubleFloat) {}

I expected to see this happen: Compiles successfully

Instead, this happened:

Before #122619, this ICEs the compiler (https://godbolt.org/z/bKn6d5jeM):

thread 'rustc' panicked at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/compiler/rustc_abi/src/lib.rs:565:13:
Size::sub: 0 - 8 would result in negative size

(see backtrace below).

After #122619, this will compile, but it will use a bizarre ABI that's probably wrong:

EDIT: I decided not to fix this ICE in #122619, since it's better to error than generate wrong code. But when the ICE is fixed, the current ABI code generates something nonsensical:

declare void @foo({ double, float, i32, i64 } inreg)

Meta

rustc --version --verbose:

rustc 1.76.0 (07dca489a 2024-02-04)
binary: rustc
commit-hash: 07dca489ac2d933c78d3c5158e3f43beefeb02ce
commit-date: 2024-02-04
host: x86_64-unknown-linux-gnu
release: 1.76.0
LLVM version: 17.0.6

(also reproducible on very recent master 766bdce)

Backtrace

thread 'rustc' panicked at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/compiler/rustc_abi/src/lib.rs:565:13:
Size::sub: 0 - 8 would result in negative size
stack backtrace:
   0:     0x7f8961a1a6f6 - std::backtrace_rs::backtrace::libunwind::trace::hbee8a7973eeb6c93
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7f8961a1a6f6 - std::backtrace_rs::backtrace::trace_unsynchronized::hc8ac75eea3aa6899
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f8961a1a6f6 - std::sys_common::backtrace::_print_fmt::hc7f3e3b5298b1083
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f8961a1a6f6 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hbb235daedd7c6190
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f8961a6cf40 - core::fmt::rt::Argument::fmt::h76c38a80d925a410
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/fmt/rt.rs:142:9
   5:     0x7f8961a6cf40 - core::fmt::write::h3ed6aeaa977c8e45
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/fmt/mod.rs:1120:17
   6:     0x7f8961a0e53f - std::io::Write::write_fmt::h78b18af5775fedb5
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/io/mod.rs:1810:15
   7:     0x7f8961a1a4d4 - std::sys_common::backtrace::_print::h5d645a07e0fcfdbb
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f8961a1a4d4 - std::sys_common::backtrace::print::h85035a511aafe7a8
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f8961a1d267 - std::panicking::default_hook::{{closure}}::hcce8cea212785a25
  10:     0x7f8961a1cfc9 - std::panicking::default_hook::hf5fcb0f213fe709a
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:292:9
  11:     0x7f895ea1461c - std[79729d9c385e1623]::panicking::update_hook::<alloc[6df67106ebca92c0]::boxed::Box<rustc_driver_impl[66ed8fdbde15dc6c]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f8961a1d9b6 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hbc5ccf4eb663e1e5
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/alloc/src/boxed.rs:2029:9
  13:     0x7f8961a1d9b6 - std::panicking::rust_panic_with_hook::h095fccf1dc9379ee
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:783:13
  14:     0x7f8961a1d702 - std::panicking::begin_panic_handler::{{closure}}::h032ba12139b353db
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:657:13
  15:     0x7f8961a1abf6 - std::sys_common::backtrace::__rust_end_short_backtrace::h9259bc2ff8fd0f76
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f8961a1d460 - rust_begin_unwind
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:645:5
  17:     0x7f8961a69645 - core::panicking::panic_fmt::h784f20a50eaab275
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/panicking.rs:72:14
  18:     0x7f895f544152 - rustc_target[edc8d30e58965941]::abi::call::sparc64::arg_scalar::<rustc_middle[e0f609162babcb92]::ty::layout::LayoutCx<rustc_middle[e0f609162babcb92]::ty::context::TyCtxt>>
  19:     0x7f895f54460d - rustc_target[edc8d30e58965941]::abi::call::sparc64::arg_scalar_pair::<rustc_middle[e0f609162babcb92]::ty::layout::LayoutCx<rustc_middle[e0f609162babcb92]::ty::context::TyCtxt>>
  20:     0x7f895f54486b - rustc_target[edc8d30e58965941]::abi::call::sparc64::parse_structure::<rustc_middle[e0f609162babcb92]::ty::Ty, rustc_middle[e0f609162babcb92]::ty::layout::LayoutCx<rustc_middle[e0f609162babcb92]::ty::context::TyCtxt>>
  21:     0x7f895f5442a2 - rustc_target[edc8d30e58965941]::abi::call::sparc64::classify_arg::<rustc_middle[e0f609162babcb92]::ty::Ty, rustc_middle[e0f609162babcb92]::ty::layout::LayoutCx<rustc_middle[e0f609162babcb92]::ty::context::TyCtxt>>
  22:     0x7f895f544a33 - rustc_target[edc8d30e58965941]::abi::call::sparc64::compute_abi_info::<rustc_middle[e0f609162babcb92]::ty::Ty, rustc_middle[e0f609162babcb92]::ty::layout::LayoutCx<rustc_middle[e0f609162babcb92]::ty::context::TyCtxt>>
  23:     0x7f89607772dc - rustc_ty_utils[112fed09b8de77ee]::abi::fn_abi_new_uncached
  24:     0x7f896018f406 - rustc_ty_utils[112fed09b8de77ee]::abi::fn_abi_of_instance
  25:     0x7f896018ddb3 - rustc_query_impl[aa9389cf74aaab3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[aa9389cf74aaab3]::query_impl::fn_abi_of_instance::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e0f609162babcb92]::query::erase::Erased<[u8; 16usize]>>
  26:     0x7f8960102553 - rustc_query_system[84cc5057ded7d916]::query::plumbing::try_execute_query::<rustc_query_impl[aa9389cf74aaab3]::DynamicConfig<rustc_query_system[84cc5057ded7d916]::query::caches::DefaultCache<rustc_middle[e0f609162babcb92]::ty::ParamEnvAnd<(rustc_middle[e0f609162babcb92]::ty::instance::Instance, &rustc_middle[e0f609162babcb92]::ty::list::List<rustc_middle[e0f609162babcb92]::ty::Ty>)>, rustc_middle[e0f609162babcb92]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[aa9389cf74aaab3]::plumbing::QueryCtxt, false>
  27:     0x7f89601021ef - rustc_query_impl[aa9389cf74aaab3]::query_impl::fn_abi_of_instance::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7f895d402af9 - <rustc_codegen_llvm[3c1678ba3e8e7d64]::context::CodegenCx as rustc_codegen_ssa[8f0ba34f7d763469]::traits::declare::PreDefineMethods>::predefine_fn
  29:     0x7f89607214a8 - rustc_codegen_llvm[3c1678ba3e8e7d64]::base::compile_codegen_unit::module_codegen
  30:     0x7f8960942a86 - <rustc_codegen_llvm[3c1678ba3e8e7d64]::LlvmCodegenBackend as rustc_codegen_ssa[8f0ba34f7d763469]::traits::backend::ExtraBackendMethods>::compile_codegen_unit
  31:     0x7f8960595746 - <rustc_codegen_llvm[3c1678ba3e8e7d64]::LlvmCodegenBackend as rustc_codegen_ssa[8f0ba34f7d763469]::traits::backend::CodegenBackend>::codegen_crate
  32:     0x7f896059331f - rustc_interface[bf5cafa581ab7832]::passes::start_codegen
  33:     0x7f8960592b22 - <rustc_interface[bf5cafa581ab7832]::queries::Queries>::codegen_and_build_linker
  34:     0x7f89608fe7a0 - rustc_interface[bf5cafa581ab7832]::interface::run_compiler::<core[f975038e3cc9791c]::result::Result<(), rustc_span[7a149c27976a99e7]::ErrorGuaranteed>, rustc_driver_impl[66ed8fdbde15dc6c]::run_compiler::{closure#0}>::{closure#0}
  35:     0x7f8960a2c7db - std[79729d9c385e1623]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[bf5cafa581ab7832]::util::run_in_thread_with_globals<rustc_interface[bf5cafa581ab7832]::interface::run_compiler<core[f975038e3cc9791c]::result::Result<(), rustc_span[7a149c27976a99e7]::ErrorGuaranteed>, rustc_driver_impl[66ed8fdbde15dc6c]::run_compiler::{closure#0}>::{closure#0}, core[f975038e3cc9791c]::result::Result<(), rustc_span[7a149c27976a99e7]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[f975038e3cc9791c]::result::Result<(), rustc_span[7a149c27976a99e7]::ErrorGuaranteed>>
  36:     0x7f8960a2c639 - <<std[79729d9c385e1623]::thread::Builder>::spawn_unchecked_<rustc_interface[bf5cafa581ab7832]::util::run_in_thread_with_globals<rustc_interface[bf5cafa581ab7832]::interface::run_compiler<core[f975038e3cc9791c]::result::Result<(), rustc_span[7a149c27976a99e7]::ErrorGuaranteed>, rustc_driver_impl[66ed8fdbde15dc6c]::run_compiler::{closure#0}>::{closure#0}, core[f975038e3cc9791c]::result::Result<(), rustc_span[7a149c27976a99e7]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[f975038e3cc9791c]::result::Result<(), rustc_span[7a149c27976a99e7]::ErrorGuaranteed>>::{closure#1} as core[f975038e3cc9791c]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  37:     0x7f8961a278e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h12de4fc57affb195
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/alloc/src/boxed.rs:2015:9
  38:     0x7f8961a278e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h3c619f45059d5cf1
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/alloc/src/boxed.rs:2015:9
  39:     0x7f8961a278e5 - std::sys::unix::thread::Thread::new::thread_start::hbac657605e4b7389
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys/unix/thread.rs:108:17
  40:     0x7f895ba94ac3 - <unknown>
  41:     0x7f895bb26850 - <unknown>
  42:                0x0 - <unknown>

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.76.0 (07dca489a 2024-02-04) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=1 -C llvm-args=--x86-asm-syntax=intel --crate-type rlib -C opt-level=3 -C debuginfo=0 -C no-prepopulate-passes

query stack during panic:
#0 [fn_abi_of_instance] computing call ABI of `foo`
end of query stack

[erikdesjardins]

Very similar to #115399, although the backtraces are a bit different--this panic occurs in sparc64::arg_scalar, that one in sparc64::classify_arg

(sparc already has a few open soundness issues, I guess this is just another one to add to the pile: https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AO-SPARC+label%3AI-unsound)

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium