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Fix pal_memory.c on OpenBSD #125010

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Fix pal_memory.c on OpenBSD #125010

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2 changes: 1 addition & 1 deletion src/native/libs/System.Native/pal_memory.c
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@
#elif HAVE_MALLOC_USABLE_SIZE_NP
#include <malloc_np.h>
#define MALLOC_SIZE(s) malloc_usable_size(s)
#elif defined(TARGET_SUNOS)
#elif defined(TARGET_OPENBSD) || defined(TARGET_SUNOS)
#define MALLOC_SIZE(s) (*((size_t*)(s)-1))
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@jkotas jkotas Feb 28, 2026

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Does this implementation actually work on OpenBSD?

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@sethjackson sethjackson Feb 28, 2026 •
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Now that I look at it again - no I do not think it will at all.

I don't think there is any implementation of malloc_size that will work. A bit unsure how to proceed here?

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@jkotas jkotas Feb 28, 2026

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This is only need for efficient implementation of aligned realloc. You should be able to provide less efficient implementation that does not depend on malloc_size

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@jkotas jkotas Feb 28, 2026

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(Every C allocator has to know the size internally to support realloc. It is unfortunate that OpenBSD does not expose it as an API. they have it as an internal macro only https://github.com/libressl/openbsd/blob/master/src/lib/libc/stdlib/malloc.c#L328-L330 .)

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@am11 am11 Mar 15, 2026 •
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malloc_usable_size was removed from OpenBSD 6.5 onwards deemed harmful: libressl/openbsd@a945275. Both OpenBSD and illumos would need manual tracking like: main...am11:runtime:patch-50. (Note: "Solaris" hasmalloc_usable_size and cmake check detects it, but illumos dropped it after OpenBSD did; seldom these two (solaris,illumos) diverge).

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@jkotas jkotas Mar 15, 2026

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Both OpenBSD and illumos would need manual tracking like: main...am11:runtime:patch-50.

The documentation says that AlignedAlloc is a thin wrapper over aligned_alloc It is intentionally speced that way to allow it to be used for interop (allocated in managed code and free in native code, and vice versa). Once you add your own tracking, it is no longer the case.

I do not think we need the tracking to implement this, albeit with some inefficiency.

void* SystemNative_AlignedRealloc(void* ptr, uintptr_t alignment, uintptr_t new_size)
{
    void* result = SystemNative_AlignedAlloc(alignment, new_size);
    if (result != NULL)
    {
#ifdef MALLOC_SIZE
        uintptr_t old_size = MALLOC_SIZE(ptr);
        assert((ptr != NULL) || (old_size == 0));

        uintptr_t size_to_copy = (new_size < old_size) ? new_size : old_size
#else
        // Less efficient implementation for platforms that do not provide MALLOC_SIZE.
        ptr = realloc(ptr, new_size);
        if (ptr == NULL)
        {
            SystemNative_AlignedFree(result);
            return NULL;
        }
        uintptr_t size_to_copy = new_size;
#endif

        memcpy(result, ptr, size_to_copy);
        SystemNative_AlignedFree(ptr);
    }

    return result;
}

#else
#error "Platform doesn't support malloc_usable_size or malloc_size"
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