linux - 是什么导致了 glBufferSubData 中的这个 opengl 段错误？

Question

一段时间以来，我一直在减少这个段错误，这是我机器上的一个非常小的可重现示例(如下)。我有一种下沉的感觉，这是一个驱动程序错误，但我对 OpenGL 非常不熟悉，所以更有可能我只是做错了什么。

这是正确的 OpenGL 3.3 代码吗？无论平台和编译器如何，都应该没问题吗？

这是代码，用gcc -ggdb -lGL -lSDL2编译

#include <stdio.h>
#include "GL/gl.h"
#include "GL/glext.h"
#include "SDL2/SDL.h"

// this section is for loading OpenGL things from later versions.

typedef void (APIENTRY *GLGenVertexArrays) (GLsizei n, GLuint *arrays);
typedef void (APIENTRY *GLGenBuffers) (GLsizei n, GLuint *buffers);
typedef void (APIENTRY *GLBindVertexArray) (GLuint array);
typedef void (APIENTRY *GLBindBuffer) (GLenum target, GLuint buffer);
typedef void (APIENTRY *GLBufferData) (GLenum target, GLsizeiptr size, const GLvoid* data, GLenum usage);
typedef void (APIENTRY *GLBufferSubData) (GLenum target, GLintptr offset, GLsizeiptr size, const GLvoid* data);
typedef void (APIENTRY *GLGetBufferSubData) (GLenum target, GLintptr offset, GLsizeiptr size, const GLvoid* data);
typedef void (APIENTRY *GLFlush) (void);
typedef void (APIENTRY *GLFinish) (void);

GLGenVertexArrays glGenVertexArrays = NULL;
GLGenBuffers glGenBuffers = NULL;
GLBindVertexArray glBindVertexArray = NULL;
GLBindBuffer glBindBuffer = NULL;
GLBufferData glBufferData = NULL;
GLBufferSubData glBufferSubData = NULL;
GLGetBufferSubData glGetBufferSubData = NULL;

void load_gl_pointers() {
  glGenVertexArrays = (GLGenVertexArrays)SDL_GL_GetProcAddress("glGenVertexArrays");
  glGenBuffers = (GLGenBuffers)SDL_GL_GetProcAddress("glGenBuffers");
  glBindVertexArray = (GLBindVertexArray)SDL_GL_GetProcAddress("glBindVertexArray");
  glBindBuffer = (GLBindBuffer)SDL_GL_GetProcAddress("glBindBuffer");
  glBufferData = (GLBufferData)SDL_GL_GetProcAddress("glBufferData");
  glBufferSubData = (GLBufferSubData)SDL_GL_GetProcAddress("glBufferSubData");
  glGetBufferSubData = (GLGetBufferSubData)SDL_GL_GetProcAddress("glGetBufferSubData");
}

// end OpenGL loading stuff


#define CAPACITY (1 << 8)

// return nonzero if an OpenGL error has occurred.
int opengl_checkerr(const char* const label) {
  GLenum err;
  switch(err = glGetError()) {
    case GL_INVALID_ENUM:
      printf("GL_INVALID_ENUM");
      break;
    case GL_INVALID_VALUE:
      printf("GL_INVALID_VALUE");
      break;
    case GL_INVALID_OPERATION:
      printf("GL_INVALID_OPERATION");
      break;
    case GL_INVALID_FRAMEBUFFER_OPERATION:
      printf("GL_INVALID_FRAMEBUFFER_OPERATION");
      break;
    case GL_OUT_OF_MEMORY:
      printf("GL_OUT_OF_MEMORY");
      break;
    case GL_STACK_UNDERFLOW:
      printf("GL_STACK_UNDERFLOW");
      break;
    case GL_STACK_OVERFLOW:
      printf("GL_STACK_OVERFLOW");
      break;
    default: return 0;
  }

  printf(" %s\n", label);
  return 1;
}

int main(int nargs, const char* args[]) {
  printf("initializing..\n");
  SDL_Init(SDL_INIT_EVERYTHING);
  SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
  SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
  SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

  SDL_Window* const w =
    SDL_CreateWindow(
      "broken",
      SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
      1, 1,
      SDL_WINDOW_OPENGL
    );

  if(w == NULL) {
    printf("window was null\n");
    return 0;
  }

  SDL_GLContext context = SDL_GL_CreateContext(w);

  if(context == NULL) {
    printf("context was null\n");
    return 0;
  }

  load_gl_pointers();

  if(opengl_checkerr("init")) {
    return 1;
  }

  printf("GL_VENDOR: %s\n", glGetString(GL_VENDOR));
  printf("GL_RENDERER: %s\n", glGetString(GL_RENDERER));

  float* const vs = malloc(CAPACITY * sizeof(float));
  memset(vs, 0, CAPACITY * sizeof(float));

  unsigned int i = 0;
  while(i < 128000) {
    GLuint vertex_array;
    GLuint vertex_buffer;

    glGenVertexArrays(1, &vertex_array);
    glBindVertexArray(vertex_array);

    glGenBuffers(1, &vertex_buffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);

    if(opengl_checkerr("gen/binding")) {
      return 1;
    }

    glBufferData(
      GL_ARRAY_BUFFER,
      CAPACITY * sizeof(float),
      vs, // initialize with `vs` just to make sure it's allocated.
      GL_DYNAMIC_DRAW
    );

    // verify that the memory is allocated by reading it back into `vs`.
    glGetBufferSubData(
      GL_ARRAY_BUFFER,
      0,
      CAPACITY * sizeof(float),
      vs
    );

    if(opengl_checkerr("creating buffer")) {
      return 1;
    }

    glFlush();
    glFinish();

    // segfault occurs here..
    glBufferSubData(
      GL_ARRAY_BUFFER,
      0,
      CAPACITY * sizeof(float),
      vs
    );

    glFlush();
    glFinish();

    ++i;
  }

  return 0;
}

当我将迭代次数从 64k 增加到 128k 时，我开始得到:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff754c859 in __memcpy_sse2_unaligned () from /usr/lib/libc.so.6
(gdb) bt
#0  0x00007ffff754c859 in __memcpy_sse2_unaligned () from /usr/lib/libc.so.6
#1  0x00007ffff2ea154d in ?? () from /usr/lib/xorg/modules/dri/i965_dri.so
#2  0x0000000000400e5c in main (nargs=1, args=0x7fffffffe8d8) at opengl-segfault.c:145

但是，我可以在没有段错误的情况下将容量增加一倍以上(将迭代次数保持在 64k)。

GL_VENDOR: Intel Open Source Technology Center
GL_RENDERER: Mesa DRI Intel(R) Haswell Mobile

Answer 1

我在调用 glGenTextures 和 glBindTexture 时遇到了非常相似的问题。我尝试调试，当我尝试逐步执行这些行时，我会得到类似以下内容的信息:

程序收到信号 SIGSEGV，段错误。
0x00007ffff26eaaa8 在 ?? () 来自/usr/lib/x86_64-linux-gnu/dri/i965_dri.so

请注意，在添加纹理之前，我可以使用 vbos 和 vaos 成功运行程序并生成良好的网格。在查看建议从 xf86-video-intel 驱动程序 切换到 xf86-video-fbdev 驱动程序的答案后，我建议不要这样做(那里关于这个问题或用户在使用集成英特尔显卡的 Linux 上面临段错误的信息真的不多。也许是一个很好的问题，可以向 Intel OpenSource 的人们提问。

我找到的解决方案是停止使用 freeglut。改用 glfw。 intel linux 图形堆栈是否真的存在一些问题，除此之外，似乎可以解决的问题是 freeglut。如果你想在你的机器上使用 glfw 最新的 opengl 核心配置文件，你只需要以下内容:

glfwWindowHint (GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint (GLFW_CONTEXT_VERSION_MINOR, 0);
glfwWindowHint (GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

设置向前兼容(虽然我看到很多帖子争论你不应该这样做)意味着 mesa 可以自由选择允许的核心上下文，将最小上下文设置为 3.0 或更高。我想 freeglut 一定是在与 mesa 的交互中出了问题，如果有人能分享一些关于这方面的信息那就太好了!