[英]why is va_arg returning wrong data?
我试图将嵌入式OS移植到新平台,并且文件系统组件遇到一些问题。 我进入了代码,终于对问题进行了定位:与我的情况相关的函数调用是
// int64_t vnid = 1;
// int32_t vid = 0;
...
vnode = queue_lookup (& vnode_manager . vnode_list,
vnode_id_inspector, vnid, vid);
这是queue_lookup声明:
void * queue_lookup (queue_t * queue, queue_inspector_t inspector, ...)
{
bool result;
va_list list, list_copy;
queue_link_t * item = NULL;
va_start (list, inspector);
if (queue -> status != 0)
{
for (item = queue -> head; item != NULL; item = item -> next)
{
result = false;
va_copy (list_copy, list);
result = inspector (item, list_copy);
va_end (list_copy);
if (result) break;
}
}
va_end (list);
return item;
}
最后是vnode_id_inspector声明:
bool vnode_id_inspector (void * node, va_list list)
{
vnode_t vnode = node;
int64_t vnid = va_arg (list, int64_t);
int32_t vid = va_arg (list, int32_t);
watch (bool)
{
ensure (vnode != NULL, false);
return vnode -> id == vnid && vnode -> volume -> id == vid;
}
}
现在的问题是,当我用vnid = 1和vid = 0调用queue_lookup时,我在vnode_id_inspector中得到了vnid = 1和vid = 1145248!
如何以尽可能少的代码更改来解决此问题?
问候,
编辑:添加一些调试信息
(gdb) p vnode_manager . vnode_list
$44 = {lock = 1, head = 0x167770, tail = 0x167770, status = 1}
(gdb) p vnode_manager . vnode_list ->head
$45 = (queue_link_t *) 0x167770
(gdb) p *(vnode_t)vnode_manager . vnode_list ->head
$46 = {link = {next = 0x0}, id = 1, volume = 0x166370, destroy = false,
usage_counter = 1, data = 0x166430}
(gdb) p *(volume_t)((vnode_t)vnode_manager . vnode_list ->head)->volume
$47 = {link = {next = 0x0}, id = 0, root_vnid = 1, lock = 0, host_volume = 0x0,
host_vnid = -1, cmd = 0x13a768 <rootfs_cmd>, data = 0x1663d0}
我解决了这个问题,堆栈对齐出现了问题。 我通过使在cpu_context_switch.s一些调整以对齐堆叠到8个字节 ,而不是4字节固定它。
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