malloc() alignment on 32 bit

Enrico Scholz enrico.scholz at sigma-chemnitz.de
Mon Sep 19 05:37:59 PDT 2022


Hello,

on an iMX6ull I stumpled across

| zstd_decomp_init:536 workspace=8ff1a004+161320
| ERROR: initcall ubifs_init+0x1/0xc4 failed: Invalid argument

which is caused by

| static int zstd_decomp_init(void)
|	void *wksp = malloc(wksp_size);
| ...
| ZSTD_DCtx* ZSTD_initStaticDCtx(void *workspace, size_t workspaceSize)
|    if ((size_t)workspace & 7) return NULL;  /* 8-aligned */


Trivial fix would be 'memalign(8, wksp_size)', but is it really ok that
malloc() for 32 bit has only an alignment of 4?

Relevant code seems to be in common/tlsf.c

| enum tlsf_private
| {
| #if defined (TLSF_64BIT)
| 	/* All allocation sizes and addresses are aligned to 8 bytes. */
| 	ALIGN_SIZE_LOG2 = 3,
| #else
| 	/* All allocation sizes and addresses are aligned to 4 bytes. */
| 	ALIGN_SIZE_LOG2 = 2,
| #endif

'ldrd/strd' require 8 byte alignment which might break with such
alignment.


Enrico



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