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Avoid trampolines in emmalloc #20496

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Oct 19, 2023
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Avoid trampolines in emmalloc #20496

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kripken Oct 19, 2023
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kripken Oct 19, 2023
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87 changes: 13 additions & 74 deletions system/lib/emmalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -71,11 +71,10 @@ static_assert((((int32_t)0x80000000U) >> 31) == -1, "This malloc implementation
static_assert(alignof(max_align_t) == 8, "max_align_t must be correct");

#ifdef EMMALLOC_NO_STD_EXPORTS
#define EMMALLOC_EXPORT
#define EMMALLOC_ALIAS(ALIAS, ORIGINAL)
#else
#define EMMALLOC_EXPORT __attribute__((weak, __visibility__("default")))
#define EMMALLOC_ALIAS(ALIAS, ORIGINAL) extern __typeof(ORIGINAL) ALIAS __attribute__((alias(#ORIGINAL)));
#define EMMALLOC_ALIAS(ALIAS, ORIGINAL) extern __typeof(ORIGINAL) ALIAS __attribute__((weak, alias(#ORIGINAL)));
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Why do we need to make these weak?

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This is to match the previous behavior.

If we don't do this then e.g. malloc would not be weak, so the user couldn't override it.

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I'm not sure that it true though.. the existing symbols are strong in that if you link the object file you are forced to take that definition. Do you have a test that fails without weak?

Overriding malloc as far as I know only works today if you don't actually use any symbols from emmalloc.o (or dlmalloc.o).

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Oh sorry. I see the existing EMMALLOC_EXPORT is weak... I'm not sure it should be but lgtm given that

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Also dlmalloc.c uses weak aliases for all of these..

#endif

#define MIN(x, y) ((x) < (y) ? (x) : (y))
Expand Down Expand Up @@ -826,13 +825,7 @@ void *emmalloc_memalign(size_t alignment, size_t size)
return ptr;
}
EMMALLOC_ALIAS(emscripten_builtin_memalign, emmalloc_memalign);

#ifndef EMMALLOC_NO_STD_EXPORTS
void * EMMALLOC_EXPORT memalign(size_t alignment, size_t size)
{
return emmalloc_memalign(alignment, size);
}
#endif
EMMALLOC_ALIAS(memalign, emmalloc_memalign);

#ifndef EMMALLOC_NO_STD_EXPORTS
void * EMMALLOC_EXPORT aligned_alloc(size_t alignment, size_t size)
Expand All @@ -848,14 +841,8 @@ void *emmalloc_malloc(size_t size)
return emmalloc_memalign(MALLOC_ALIGNMENT, size);
}
EMMALLOC_ALIAS(emscripten_builtin_malloc, emmalloc_malloc);
EMMALLOC_ALIAS(__libc_malloc, emmalloc_malloc);

#ifndef EMMALLOC_NO_STD_EXPORTS
void * EMMALLOC_EXPORT malloc(size_t size)
{
return emmalloc_malloc(size);
}
#endif
EMMALLOC_ALIAS(__libc_malloc, emmalloc_malloc);
EMMALLOC_ALIAS(malloc, emmalloc_malloc);

size_t emmalloc_usable_size(void *ptr)
{
Expand All @@ -876,13 +863,7 @@ size_t emmalloc_usable_size(void *ptr)

return size - REGION_HEADER_SIZE;
}

#ifndef EMMALLOC_NO_STD_EXPORTS
size_t EMMALLOC_EXPORT malloc_usable_size(void *ptr)
{
return emmalloc_usable_size(ptr);
}
#endif
EMMALLOC_ALIAS(malloc_usable_size, emmalloc_usable_size);

void emmalloc_free(void *ptr)
{
Expand Down Expand Up @@ -954,14 +935,8 @@ void emmalloc_free(void *ptr)
#endif
}
EMMALLOC_ALIAS(emscripten_builtin_free, emmalloc_free);
EMMALLOC_ALIAS(__libc_free, emmalloc_free);

#ifndef EMMALLOC_NO_STD_EXPORTS
void EMMALLOC_EXPORT free(void *ptr)
{
return emmalloc_free(ptr);
}
#endif
EMMALLOC_ALIAS(__libc_free, emmalloc_free);
EMMALLOC_ALIAS(free, emmalloc_free);

// Can be called to attempt to increase or decrease the size of the given region
// to a new size (in-place). Returns 1 if resize succeeds, and 0 on failure.
Expand Down Expand Up @@ -1089,13 +1064,7 @@ void *emmalloc_aligned_realloc(void *ptr, size_t alignment, size_t size)
// null pointer is returned.
return newptr;
}

#ifndef EMMALLOC_NO_STD_EXPORTS
void * EMMALLOC_EXPORT aligned_realloc(void *ptr, size_t alignment, size_t size)
{
return emmalloc_aligned_realloc(ptr, alignment, size);
}
#endif
EMMALLOC_ALIAS(aligned_realloc, emmalloc_aligned_realloc);

// realloc_try() is like realloc(), but only attempts to try to resize the existing memory
// area. If resizing the existing memory area fails, then realloc_try() will return 0
Expand Down Expand Up @@ -1180,13 +1149,7 @@ void *emmalloc_realloc(void *ptr, size_t size)
return emmalloc_aligned_realloc(ptr, MALLOC_ALIGNMENT, size);
}
EMMALLOC_ALIAS(__libc_realloc, emmalloc_realloc);

#ifndef EMMALLOC_NO_STD_EXPORTS
void * EMMALLOC_EXPORT realloc(void *ptr, size_t size)
{
return emmalloc_realloc(ptr, size);
}
#endif
EMMALLOC_ALIAS(realloc, emmalloc_realloc);

// realloc_uninitialized() is like realloc(), but old memory contents
// will be undefined after reallocation. (old memory is not preserved in any case)
Expand All @@ -1203,13 +1166,7 @@ int emmalloc_posix_memalign(void **memptr, size_t alignment, size_t size)
*memptr = emmalloc_memalign(alignment, size);
return *memptr ? 0 : 12/*ENOMEM*/;
}

#ifndef EMMALLOC_NO_STD_EXPORTS
int EMMALLOC_EXPORT posix_memalign(void **memptr, size_t alignment, size_t size)
{
return emmalloc_posix_memalign(memptr, alignment, size);
}
#endif
EMMALLOC_ALIAS(posix_memalign, emmalloc_posix_memalign);

void *emmalloc_calloc(size_t num, size_t size)
{
Expand All @@ -1220,13 +1177,7 @@ void *emmalloc_calloc(size_t num, size_t size)
return ptr;
}
EMMALLOC_ALIAS(__libc_calloc, emmalloc_calloc);

#ifndef EMMALLOC_NO_STD_EXPORTS
void * EMMALLOC_EXPORT calloc(size_t num, size_t size)
{
return emmalloc_calloc(num, size);
}
#endif
EMMALLOC_ALIAS(calloc, emmalloc_calloc);

static int count_linked_list_size(Region *list)
{
Expand Down Expand Up @@ -1316,13 +1267,7 @@ struct mallinfo emmalloc_mallinfo()
MALLOC_RELEASE();
return info;
}

#ifndef EMMALLOC_NO_STD_EXPORTS
struct mallinfo EMMALLOC_EXPORT mallinfo()
{
return emmalloc_mallinfo();
}
#endif
EMMALLOC_ALIAS(mallinfo, emmalloc_mallinfo);

// Note! This function is not fully multithreading safe: while this function is running, other threads should not be
// allowed to call sbrk()!
Expand Down Expand Up @@ -1384,13 +1329,7 @@ int emmalloc_trim(size_t pad)
MALLOC_RELEASE();
return success;
}

#ifndef EMMALLOC_NO_STD_EXPORTS
int EMMALLOC_EXPORT malloc_trim(size_t pad)
{
return emmalloc_trim(pad);
}
#endif
EMMALLOC_ALIAS(malloc_trim, emmalloc_trim)

size_t emmalloc_dynamic_heap_size()
{
Expand Down