Skip to content

c-variadic: make va_arg match on Arch exhaustive #150831

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
folkertdev wants to merge 2 commits into
base: main
Choose a base branch
from
Open

c-variadic: make va_arg match on Arch exhaustive #150831

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
09864b6
c-variadic: minor cleanups of `va_arg`
folkertdev Jan 8, 2026
b388d92
c-variadic: make va_arg match on `Arch` exhaustive
folkertdev Jan 8, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
88 changes: 64 additions & 24 deletions compiler/rustc_codegen_llvm/src/va_arg.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -131,7 +131,7 @@ fn emit_ptr_va_arg<'ll, 'tcx>(
);
if indirect {
let tmp_ret = bx.load(llty, addr, addr_align);
bx.load(bx.cx.layout_of(target_ty).llvm_type(bx.cx), tmp_ret, align.abi)
bx.load(layout.llvm_type(bx.cx), tmp_ret, align.abi)
} else {
bx.load(llty, addr, addr_align)
}
Expand Down Expand Up @@ -1007,6 +1007,8 @@ fn emit_xtensa_va_arg<'ll, 'tcx>(

/// Determine the va_arg implementation to use. The LLVM va_arg instruction
/// is lacking in some instances, so we should only use it as a fallback.
///
/// <https://llvm.org/docs/LangRef.html#va-arg-instruction>
pub(super) fn emit_va_arg<'ll, 'tcx>(
bx: &mut Builder<'_, 'll, 'tcx>,
addr: OperandRef<'tcx, &'ll Value>,
Expand All @@ -1015,6 +1017,10 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
let layout = bx.cx.layout_of(target_ty);
let target_ty_size = layout.layout.size().bytes();

// Some ABIs have special behavior for zero-sized types. currently `VaArgSafe` is not
// implemented for any zero-sized types, so this assert should always hold.
assert!(!bx.layout_of(target_ty).is_zst());

let target = &bx.cx.tcx.sess.target;
match target.arch {
Arch::X86 => emit_ptr_va_arg(
Expand All @@ -1026,17 +1032,24 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
if target.is_like_windows { AllowHigherAlign::No } else { AllowHigherAlign::Yes },
ForceRightAdjust::No,
),
Arch::AArch64 | Arch::Arm64EC if target.is_like_windows || target.is_like_darwin => {
emit_ptr_va_arg(
bx,
addr,
target_ty,
PassMode::Direct,
SlotSize::Bytes8,
if target.is_like_windows { AllowHigherAlign::No } else { AllowHigherAlign::Yes },
ForceRightAdjust::No,
)
}
Arch::Arm64EC => emit_ptr_va_arg(
bx,
addr,
target_ty,
PassMode::Direct,
SlotSize::Bytes8,
if target.is_like_windows { AllowHigherAlign::No } else { AllowHigherAlign::Yes },
ForceRightAdjust::No,
),
Arch::AArch64 if target.is_like_windows || target.is_like_darwin => emit_ptr_va_arg(
bx,
addr,
target_ty,
PassMode::Direct,
SlotSize::Bytes8,
if target.is_like_windows { AllowHigherAlign::No } else { AllowHigherAlign::Yes },
ForceRightAdjust::No,
),
Arch::AArch64 => emit_aapcs_va_arg(bx, addr, target_ty),
Arch::Arm => {
// Types wider than 16 bytes are not currently supported. Clang has special logic for
Expand Down Expand Up @@ -1073,7 +1086,16 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
AllowHigherAlign::Yes,
ForceRightAdjust::No,
),
Arch::LoongArch32 => emit_ptr_va_arg(
Arch::RiscV32 if target.abi == Abi::Ilp32e => {
// FIXME: clang manually adjusts the alignment for this ABI. It notes:
//
// > To be compatible with GCC's behaviors, we force arguments with
// > 2×XLEN-bit alignment and size at most 2×XLEN bits like `long long`,
// > `unsigned long long` and `double` to have 4-byte alignment. This
// > behavior may be changed when RV32E/ILP32E is ratified.
bx.va_arg(addr.immediate(), bx.cx.layout_of(target_ty).llvm_type(bx.cx))
}
Arch::RiscV32 | Arch::LoongArch32 => emit_ptr_va_arg(
Comment on lines -1076 to +1098
Copy link
Contributor Author

@folkertdev folkertdev Jan 8, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

https://github.com/llvm/llvm-project/blob/289a3292be0c6a3df86bcdf5be7dd05b79a5570c/clang/lib/CodeGen/Targets/RISCV.cpp#L756

bx,
addr,
target_ty,
Expand All @@ -1082,7 +1104,7 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
AllowHigherAlign::Yes,
ForceRightAdjust::No,
),
Arch::LoongArch64 => emit_ptr_va_arg(
Arch::RiscV64 | Arch::LoongArch64 => emit_ptr_va_arg(
bx,
addr,
target_ty,
Expand Down Expand Up @@ -1149,16 +1171,34 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
// This includes `target.is_like_darwin`, which on x86_64 targets is like sysv64.
Arch::X86_64 => emit_x86_64_sysv64_va_arg(bx, addr, target_ty),
Arch::Xtensa => emit_xtensa_va_arg(bx, addr, target_ty),
Arch::Hexagon => {
if target.env == Env::Musl {
emit_hexagon_va_arg_musl(bx, addr, target_ty)
} else {
emit_hexagon_va_arg_bare_metal(bx, addr, target_ty)
}
Arch::Hexagon => match target.env {
Env::Musl => emit_hexagon_va_arg_musl(bx, addr, target_ty),
_ => emit_hexagon_va_arg_bare_metal(bx, addr, target_ty),
},
Arch::Sparc64 => emit_ptr_va_arg(
bx,
addr,
target_ty,
if target_ty_size > 2 * 8 { PassMode::Indirect } else { PassMode::Direct },
SlotSize::Bytes8,
AllowHigherAlign::Yes,
ForceRightAdjust::No,
),
Comment on lines +1178 to +1186
Copy link
Contributor Author

@folkertdev folkertdev Jan 8, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

https://github.com/llvm/llvm-project/blob/289a3292be0c6a3df86bcdf5be7dd05b79a5570c/clang/lib/CodeGen/Targets/Sparc.cpp#L327


Arch::Bpf => bug!("bpf does not support c-variadic functions"),
Arch::SpirV => bug!("spirv does not support c-variadic functions"),

Arch::Mips | Arch::Mips32r6 | Arch::Mips64 | Arch::Mips64r6 => {
// FIXME: port MipsTargetLowering::lowerVAARG.
Copy link
Contributor Author

@folkertdev folkertdev Jan 8, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The implementation is at https://github.com/llvm/llvm-project/blob/289a3292be0c6a3df86bcdf5be7dd05b79a5570c/llvm/lib/Target/Mips/MipsISelLowering.cpp#L2338

I suspect that is ultimately just emitVoidPtrVAArg but it's hard to tell.

bx.va_arg(addr.immediate(), bx.cx.layout_of(target_ty).llvm_type(bx.cx))
}
Arch::Sparc | Arch::Avr | Arch::M68k | Arch::Msp430 => {
// Clang uses the LLVM implementation for these architectures.
bx.va_arg(addr.immediate(), bx.cx.layout_of(target_ty).llvm_type(bx.cx))
}
Comment on lines +1195 to +1198
Copy link
Contributor Author

@folkertdev folkertdev Jan 8, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

That implementation is via DefaultABIInfo::EmitVAArg

https://github.com/llvm/llvm-project/blob/c379a88c09af4657d609888a46ada7719b2c9da9/clang/lib/CodeGen/ABIInfoImpl.cpp#L77-L83

To EmitVAArgInstr

https://github.com/llvm/llvm-project/blob/c379a88c09af4657d609888a46ada7719b2c9da9/clang/lib/CodeGen/ABIInfoImpl.cpp#L404

To the LLVM CreateVAArg I believe this will eventually call expandVAArg

https://github.com/llvm/llvm-project/blob/21a1e6e6a70d70635c68b9aaa54f816ae36a6416/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp#L2515

That really looks like emitVoidPtrVAArg to me, but it's hard to be completely sure.

Arch::Other(_) => {
// For custom targets, use the LLVM va_arg instruction as a fallback.
bx.va_arg(addr.immediate(), bx.cx.layout_of(target_ty).llvm_type(bx.cx))
}
// For all other architecture/OS combinations fall back to using
// the LLVM va_arg instruction.
// https://llvm.org/docs/LangRef.html#va-arg-instruction
_ => bx.va_arg(addr.immediate(), bx.cx.layout_of(target_ty).llvm_type(bx.cx)),
}
}
Loading