The malloc_very_large() test fails when mcheck is enabled with large CONFIG_MCHECK_CALLER_LEN because the 64K margin does not account for the per-allocation overhead (header + canaries). Use a larger margin (256K) when mcheck is enabled to ensure the test passes regardless of the mcheck caller length setting. Co-developed-by: Claude <noreply@anthropic.com> Signed-off-by: Simon Glass <simon.glass@canonical.com>