opengl - Valgrind:libnvidia-glcore.so.346.47 条件跳转或移动取决于未初始化的值

Question

当针对我的动态库运行我的测试 c++ 应用程序时，我的动态库与 NVIDIA 的 libGL.so 链接。所以我收到了 Valgrind 报告的以下错误(见下文)。我很想压制它们，但我不确定这是我的问题还是 libnvidia-glcore.so 的问题。部分不确定性源于不完全理解 Valgrind 的输出。我已经在调用 glXCreateContextAttribsARB 时查看了我的代码中哪些变量可能未初始化。但我在那里看不到任何东西。如果它从输出显示到我的问题，我在寻找什么类型的东西？我得到的两个错误是:

==10156== Conditional jump or move depends on uninitialised value(s)
==10156==    at 0x7E4CAF4: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7DEE0CD: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7DEEADC: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F75DA1: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F775D3: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7E279BE: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7E27D21: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F760F5: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F3E353: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7A8C9C0: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x4E535F2: opengl_core::render_system::init() (x11_render_system.cpp:92)
==10156==    by 0x4040D8: test_render_system::run() (test_x11_render_system.cpp:10)
==10156==  Uninitialised value was created by a heap allocation
==10156==    at 0x4C29BCF: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==10156==    by 0x5116428: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x7EECF2E: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7E479C1: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7DC8C31: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x50BF331: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x50EB72A: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x50EEA87: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x50E47D2: glXCreateContextAttribsARB (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x4E52EF8: opengl_core::render_context::init(opengl_core::render_window&, opengl_core::fb_config&) (x11_render_context.cpp:120)
==10156==    by 0x4E534D0: opengl_core::render_system::init() (x11_render_system.cpp:65)
==10156==    by 0x4040D8: test_render_system::run() (test_x11_render_system.cpp:10)
==10156== 

==10156== Conditional jump or move depends on uninitialised value(s)
==10156==    at 0x7E4CAF4: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7DEE0CD: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7DF085F: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F4B78B: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F4CFBC: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7E279BE: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7E27D21: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F4BFE0: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F38ED5: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7B20F52: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7F3E2CB: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7A8C9C0: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==  Uninitialised value was created by a heap allocation
==10156==    at 0x4C29BCF: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==10156==    by 0x5116428: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x7EECF2E: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7E479C1: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x7DC8C31: ??? (in /usr/lib64/nvidia/libnvidia-glcore.so.346.47)
==10156==    by 0x50BF331: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x50EB72A: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x50EEA87: ??? (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x50E47D2: glXCreateContextAttribsARB (in /usr/lib64/nvidia/libGL.so.346.47)
==10156==    by 0x4E52EF8: opengl_core::render_context::init(opengl_core::render_window&, opengl_core::fb_config&) (x11_render_context.cpp:120)
==10156==    by 0x4E534D0: opengl_core::render_system::init() (x11_render_system.cpp:65)
==10156==    by 0x4040D8: test_render_system::run() (test_x11_render_system.cpp:10)
==10156== 

按要求:

 // src/x11_render_system.cpp
 91       m_impl->m_context.make_current(m_impl->m_window);
 92       glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 93       glClearColor(1.0, 0.0, 0.0, 1.0);  
 94       glXSwapBuffers(display, window);   
 95       m_impl->m_context.make_not_current();

Answer 1

由于关键硬件驱动程序(例如 GPU 驱动程序)的工作方式，Valgrind 很容易误报。基本上，这些驱动程序通过由 BIOS 设置的用户空间(虚拟 RAM)访问 GPU 的内存(甚至 寄存器 )(这是工作中的 POSIX mmap)。这样，驱动程序可以通过任意地址访问设备的寄存器，就像任何其他变量一样。

关键是某些设备的寄存器仅用于读取。例如，它们可以反射(reflect)设备的某些状态。因此，只有设备才有理由写入它们(即使 CPU 尝试这样做，它也会失败)。大多数情况下，它在上电时在内部执行此操作，并且不时在状态更改时执行此操作，并在设置映射时反射(reflect)到用户空间。本质上，这些是纯粹的易变变量……甚至比通常的线程到线程概念更易变，顺便说一下，Valgrind 很好地处理了它，因为它模拟了 CPU。

但是 Valgrind 生活在一个确定性的世界(CPU 和 RAM)，而这些 GPU 的寄存器完全不属于这个世界。当驱动程序读取它们时，Valgrind 只是认为它正在访问 RAM(由于 mmap)，这绝对不是真的。因此，当驱动程序使用读取的数据(某些设备状态)进行相应的分支时，Valgrind 报告说，因为它的世界中没有任何东西写过这些数据。

老实说:专有驱动程序不是开源的，所以很难猜测到底发生了什么，但很可能是类似的。我可以肯定的是，这种情况发生在 Valgrind 和 GPU 驱动程序上(即使是非常小的程序)，主要是在初始化期间，每个人都同意这些是误报。因此，您可以放心地忽略它...或在您的项目中为 Valgrind 创建一个抑制文件(让我们将其命名为 valgrind.supp):

{
  NVidia-driver
  Memcheck:Cond
  obj:/usr/lib64/nvidia/libnvidia-glcore.so.346.47
}

然后您使用选项 --suppressions=valgrind.supp 调用 Valgrind，它将不再报告这些误报。

您可能有与此相关的其他驱动程序对象，只需为它们添加条目(您必须重复整个 {...} 并修改对象行以匹配 Valgrind 报告的内容)。由于版本更改，您可能还需要在每次更新驱动程序时更新它们，但我想您可以使用基本的通配符来避免这种情况。

看看 here有关此 Valgrind 功能的更多信息。