From e7d1503eff32deeb679fbfb77eb9f83a60f1b116 Mon Sep 17 00:00:00 2001 From: Gabriel Corona Date: Thu, 19 Jun 2014 15:33:12 +0200 Subject: [PATCH] [mc] Avoid big alloca in mc_snapshot_region_memcp and mc_snapshot_memcp Be more stack friendly. --- src/mc/mc_snapshot.c | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-) diff --git a/src/mc/mc_snapshot.c b/src/mc/mc_snapshot.c index c733664f01..33f670c84e 100644 --- a/src/mc/mc_snapshot.c +++ b/src/mc/mc_snapshot.c @@ -4,6 +4,8 @@ /* This program is free software; you can redistribute it and/or modify it * under the terms of the license (GNU LGPL) which comes with this package. */ +#include + #include "mc_private.h" #include "mc_mmu.h" @@ -160,13 +162,23 @@ int mc_snapshot_region_memcp( void* addr1, mc_mem_region_t region1, void* addr2, mc_mem_region_t region2, size_t size) { - // TODO, optimize this, avoid alloca - void* buffer1 = mc_snapshot_read_region(addr1, region1, alloca(size), size); - void* buffer2 = mc_snapshot_read_region(addr2, region2, alloca(size), size); + // Using alloca() for large allocations may trigger stack overflow: + // use malloc if the buffer is too big. + + bool stack_alloc = size < 64; + void* buffer = stack_alloc ? alloca(2*size) : malloc(2*size); + void* buffer1 = mc_snapshot_read_region(addr1, region1, buffer, size); + void* buffer2 = mc_snapshot_read_region(addr2, region2, (char*) buffer + size, size); + int res; if (buffer1 == buffer2) { - return 0; + res = 0; + } else { + res = memcmp(buffer1, buffer2, size); + } + if (!stack_alloc) { + free(buffer); } - return memcmp(buffer1, buffer2, size); + return res; } /** Compare memory between snapshots @@ -181,11 +193,7 @@ int mc_snapshot_memcp( void* addr1, mc_snapshot_t snapshot1, void* addr2, mc_snapshot_t snapshot2, size_t size) { - // TODO, optimize this, avoid alloca - void* buffer1 = mc_snapshot_read(addr1, snapshot1, alloca(size), size); - void* buffer2 = mc_snapshot_read(addr2, snapshot2, alloca(size), size); - if (buffer1 == buffer2) { - return 0; - } - return memcmp(buffer1, buffer2, size); + mc_mem_region_t region1 = mc_get_snapshot_region(addr1, snapshot1); + mc_mem_region_t region2 = mc_get_snapshot_region(addr2, snapshot2); + return mc_snapshot_region_memcp(addr1, region1, addr2, region2, size); } -- 2.20.1