在 64 位操作系统上以 32 位模式和 64 位模式编译关于 ioctl 函数的执行有何不同?

问题描述

我有一个 64 位的 Enterprise SuSE 11我有一个应用程序，它打开 HIDRAW 设备并在其上运行 ioctl 函数以从该设备获取原始信息，如下所示:

struct hidraw_devinfo devinfo;int fd = open("/dev/hidraw0", 0);int ret = ioctl(fd, HIDIOCGRAWINFO, &devinfo);...

如果我在 64 位模式下编译这个程序，没有错误也没有问题，当我执行应用程序时，ioctl 函数正常工作.

g++ main.cpp

如果我在 32 位模式下编译这个程序，也没有错误也没有问题.但是当我执行应用程序时，ioctl 函数返回 EINVAL 错误(errno = 22 , Invalid Argument)

g++ -m32 main.cpp

有什么问题吗?

注意:

struct hidraw_devinfo{__u32 总线类型；__s16 供应商；__s16 产品；}

解决方案

Linux ioctl 定义和兼容性层是我刚刚猛烈抨击的一个引人入胜的话题.

通常 ioctl 定义使用一系列宏 _IOW/_IOR 等，这些宏将您的参数类型名称作为参考，以及一个幻数和序数值，这些宏被修改为您的 ioctl参数值(例如 HIDIOCGRAWINFO).类型名称用于将 sizeof(arg_type) 编码到定义中.这意味着 user 空间中使用的类型决定了 ioctl 宏生成的 value - 即 HIDIOCGRAWINFO 可能因包含条件而异.>

这是 32 位和 64 位不同的第一点，sizeof 可能会有所不同，具体取决于包装、模糊数据大小(例如 long)的使用，但尤其是(并且不可避免)如果您使用指针参数.因此，在这种情况下，想要支持 32 位客户端的 64 位内核模块需要定义兼容性参数类型以匹配 32 位等效参数类型的布局，从而匹配 32 位兼容 ioctl.这些 32 位等效定义使用名为 compat 的内核工具/层.

在您的情况下，sizeof() 是相同的，因此这不是您要采取的路径 - 但了解可能发生的全部情况很重要.

此外，内核配置可以定义 CONFIG_COMPAT 来更改系统调用包装器(尤其是围绕用户/内核接口 wrt ioctl 的代码)以减轻负担支持 32 位和 64 位.其中一部分包括一个名为 ioctl_compat 的兼容性 ioctl 回调.

我所看到的是 CONFIG_COMPAT 定义了 32 位程序将生成将 ioctl 传递给 ioctl_compat 回调的代码，即使它可以生成与 64 位相同的 ioctl 值(例如在您的情况下).因此，驱动程序编写者需要确保 ioctl_compat 处理两者特殊的(不同的)32 位兼容 ioctl 类型和正常的64-位 - 或未更改的 32 位"类型.

因此，在仅 32 位和仅 64 位系统(没有 CONFIG_COMPAT)上设计和测试的内核模块可能适用于 32 位和 64 位程序，但不适用于同时支持两者的程序.

所以查看 HID 我看到这是在 2.6.38 中添加的:

http://lxr.linux.no/#linux+v2.6.38/drivers/hid/hidraw.c#L347

I have a 64 bit Enterprice SuSE 11I have an application which open a HIDRAW device and operate an ioctl function on it to get raw info from this device like below:

struct hidraw_devinfo devinfo;
int fd = open("/dev/hidraw0", 0);
int ret = ioctl(fd, HIDIOCGRAWINFO, &devinfo);
...

If I compile this program in 64 bit mode there is no error and no problem and when I execute the application the ioctl function works properly.

g++ main.cpp

If I complie this program in 32 bit mode there is also no error and no problem. but when I execute the application the ioctl function return EINVAL error(errno = 22 , Invalid Argument)

g++ -m32 main.cpp

what's the problem?

Note:

struct hidraw_devinfo
{
     __u32 bustype;
     __s16 vendor;
     __s16 product;
}

解决方案

Linux ioctl definitions and compatibility layers are a fascinating topic I've just bashed my head against.

Typically ioctl definitions use a family of macros _IOW/_IOR et al that take your argument type-name as a reference, along with a magic number and ordinal value that are munged to give you your ioctl argument value (eg HIDIOCGRAWINFO). The type-name is used to encode sizeof(arg_type) into the definition. This means that the type used in user space determines the value generated by the ioctl macro - ie HIDIOCGRAWINFO may vary based on include conditions.

Here is the first point where 32- and 64-bit differ, the sizeof may differ, depending on packing, use of vague data-sizes (eg long), but especially (and unavoidably) if you use a pointer argument. So in this case a 64-bit kernel module what wants to support 32-bit clients needs do define a compatibility argument-type to match the layout of the 32-bit equivalent of the argument type and thus a 32-bit compatible ioctl. These 32-bit equivalent definitions make use of a kernel facility/layer called compat.

In your case the sizeof() is the same so that is not the path you are taking - but its important to understand the whole of what could be happening.

In addition a kernel configuration may define CONFIG_COMPAT which changes the sys-call wrappers (especially the code surrounding the user/kernel interface wrt ioctl) to ease the burden of supporting 32- and 64-bit. Part of this includes a compatibility ioctl callback called ioctl_compat.

What I've seen is with CONFIG_COMPAT defined that 32-bit programs will generate code that delivers ioctls to the ioctl_compat callback, even if it could generate the same ioctl value as 64-bit does (eg in your case). So the driver writer needs to make sure that ioctl_compat handles both the special (different) 32-bit compatible ioctl TYPEs and the normal "64-bit - or unchanged 32-bit" types.

So a kernel-module designed and tested on 32-bit only and 64-bit only systems (without CONFIG_COMPAT) may work for 32- and 64-bit programs, but not for one which supports both.

So looking in HID I see this was added in 2.6.38:

http://lxr.linux.no/#linux+v2.6.38/drivers/hid/hidraw.c#L347

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