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Compiling for 32bit Linux #4371

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ax3l opened this issue Mar 12, 2025 · 8 comments · Fixed by #4375
Closed

Compiling for 32bit Linux #4371

ax3l opened this issue Mar 12, 2025 · 8 comments · Fixed by #4375
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@ax3l
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ax3l commented Mar 12, 2025

Compiling AMReX 25.02 for 32bit Linux raises this static assert:

src/Particle/ParticleContainer.cpp:52:8:   required from here
2025-03-12T17:03:32.0388802Z   /usr/local/include/AMReX_ParticleContainerI.H:65:61: error: static assertion failed: sizeof ParticleType is not a multiple of sizeof RealType
2025-03-12T17:03:32.0390003Z      65 |         static_assert(sizeof(ParticleType)%sizeof(RealType) == 0,
2025-03-12T17:03:32.0390575Z         |                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~

https://github.com/AMReX-Codes/amrex/blob/25.02/Src/Particle/AMReX_ParticleContainerI.H#L65-L66

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@ax3l ax3l added the bug label Mar 12, 2025
@ax3l ax3l mentioned this issue Mar 12, 2025
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@ax3l
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ax3l commented Mar 12, 2025

@atmyers @WeiqunZhang is this potentially an easy fix?

@WeiqunZhang
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What's the data type of ParticleType? We can probably use alignas on it to work around the issue. Or maybe the function containing the static_assert can be relaxed.

@ax3l
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ax3l commented Mar 14, 2025 •
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The data type should be a double for ParticleReal for pure SoA particles, I am seeing this with a default build of ImpactX using Python bindings on 32bit Linux.

The problem is likely from some integer types that we also store in ParticleType?

@ax3l
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ax3l commented Mar 14, 2025 •
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Type seems to be this: amrex::SoAParticle<3, 0>

ParticleContainer.cpp:52:8:   required from here
2025-03-13T08:33:47.7341772Z   /usr/local/include/AMReX_ParticleContainerI.H:65:61: error: static assertion failed: sizeof ParticleType is not a multiple of sizeof RealType
2025-03-13T08:33:47.7342864Z      65 |         static_assert(sizeof(ParticleType)%sizeof(RealType) == 0,
2025-03-13T08:33:47.7343420Z         |                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
2025-03-13T08:33:47.9897603Z   /usr/local/include/AMReX_ParticleContainerI.H: In instantiation of ‘void amrex::ParticleContainer_impl<ParticleType, NArrayReal, NArrayInt, Allocator, CellAssignor>::Initialize() [with T_ParticleType = amrex::SoAParticle<3, 0>; int T_NArrayReal = 3; int T_NArrayInt = 0; Allocator = std::allocator; T_CellAssignor = amrex::DefaultAssignor]’:

Accidentally cropped the one line that counts in the initial report, haha.

@WeiqunZhang
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I don't understand. It looks like that the first non-static member of SoAParticle<3, 0> is long long. That should make the size of the class a multiple of 8, assuming long long needs to be aligned with 8.

@WeiqunZhang
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Oh I see. ChatGPT says,

On an i686 (32-bit x86) system, the alignment of long long depends on the ABI (Application Binary Interface) used.
Alignment of long long on i686 (x86, 32-bit):

    System V i386 ABI (Used by Linux, including Alpine Linux with musl)
        Alignment of long long: 4 bytes
        Size of long long: 8 bytes
        This means that long long can be stored at 4-byte aligned addresses instead of 8-byte aligned addresses.

Why is long long only 4-byte aligned on i686?

    On x86 (32-bit), most data types do not require strict alignment.
    The i386 System V ABI specifies that long long should be aligned to 4 bytes, not 8.
    This differs from architectures like x86_64, where long long is 8-byte aligned.

@WeiqunZhang WeiqunZhang linked a pull request Mar 14, 2025 that will close this issue
Force the alignment of SoA and AoS Particles #4375
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@ax3l Could you test #4375?

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https://en.wikipedia.org/wiki/Data_structure_alignment

A long long (eight bytes) will be 8-byte aligned on Windows and 4-byte aligned on Linux (8-byte with -malign-double compile time option).

@ax3l ax3l mentioned this issue Mar 14, 2025
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atmyers pushed a commit that referenced this issue Mar 26, 2025
@WeiqunZhang
Force the alignment of SoA and AoS Particles (#4375)

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546cc5e 
This fixes build issues on 32-bit Linux. This should not affect 64 bits
machines.

Fix #4371
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Force the alignment of SoA and AoS Particles WeiqunZhang/amrex
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