c_variadic: provide our own va_arg implementation for more targets
#150094
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rustbot
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A-LLVM
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folkertdev
commented
Dec 17, 2025
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| Arch::LoongArch32 => emit_ptr_va_arg( | ||
| bx, | ||
| addr, | ||
| target_ty, | ||
| if target_ty_size > 2 * 4 { PassMode::Indirect } else { PassMode::Direct }, | ||
| SlotSize::Bytes4, | ||
| AllowHigherAlign::Yes, | ||
| ForceRightAdjust::No, | ||
| ), | ||
| Arch::LoongArch64 => 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, | ||
| ), |
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zero-sized types can't reach this logic currently, but we could handle them. This logic is very similar for riscv, but it has an annoying exception for the 32-bit embedded ABI which lowers alignment for f64 and i64/u64 from 8 to 4. Apparently that may change as things are ratified.
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| Arch::AmdGpu => emit_ptr_va_arg( | ||
| bx, | ||
| addr, | ||
| target_ty, | ||
| PassMode::Direct, | ||
| SlotSize::Bytes4, | ||
| AllowHigherAlign::No, | ||
| ForceRightAdjust::No, | ||
| ), |
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| Arch::Nvptx64 => emit_ptr_va_arg( | ||
| bx, | ||
| addr, | ||
| target_ty, | ||
| PassMode::Direct, | ||
| SlotSize::Bytes1, | ||
| AllowHigherAlign::Yes, | ||
| ForceRightAdjust::No, | ||
| ), |
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| Arch::Wasm32 | Arch::Wasm64 => emit_ptr_va_arg( | ||
| bx, | ||
| addr, | ||
| target_ty, | ||
| if layout.is_aggregate() || layout.is_zst() || layout.is_1zst() { | ||
| PassMode::Indirect | ||
| } else { | ||
| PassMode::Direct | ||
| }, | ||
| SlotSize::Bytes4, | ||
| AllowHigherAlign::Yes, | ||
| ForceRightAdjust::No, | ||
| ), |
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curiously the slot size is always 4, independent of whether wasm32 or wasm64 is used. I suppose that may change in the future if/when wasm64 gets more attention.
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| Arch::CSky => emit_ptr_va_arg( | ||
| bx, | ||
| addr, | ||
| target_ty, | ||
| PassMode::Direct, | ||
| SlotSize::Bytes4, | ||
| AllowHigherAlign::Yes, | ||
| ForceRightAdjust::No, | ||
| ), |
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tracking issue: #44930
Provide our own implementations in order to guarantee the behavior of
va_arg. We will only be able to stabilizec_variadicon targets where we know and guarantee the properties ofva_arg.r? workingjubilee