Created attachment 1304 [details]
Self-contained test case.

SDL_GL_GetAttribute(SDL_GL_RED_SIZE) etc. fails for core profiles because it's using deprecated/removed OpenGL functionality. Here's a self-contained repro (I'm using mingw-w64 on Win7 x64, but the problem is universal):

C:\Temp\gcc>type meow.cpp
// g++ -DUSE_CORE_PROFILE -Wall -Wextra -mwindows meow.cpp -o meow.exe -lopengl32 -lSDL2 -limm32 -lole32 -loleaut32 -luuid -lversion -lwinmm -lmingw32 -lSDL2main

#include <stddef.h>
#include <fstream>
#include <GL/gl.h>
#include <SDL2/SDL.h>

struct Attribute {
    SDL_GLattr attr;
    int value;
    const char * name;
};

int main(int, char * []) {
    std::ofstream f("output.txt");

#ifdef USE_CORE_PROFILE
    f << "Using core profile.\n";
#else
    f << "Using compatibility profile.\n";
#endif

    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        f << "SDL_Init() failed!\n";
    }

    #define ATTRIB(ATTR, VALUE) { ATTR, VALUE, #ATTR }

    const Attribute attrs[] = {
        ATTRIB(  SDL_GL_RED_SIZE, 8),
        ATTRIB(SDL_GL_GREEN_SIZE, 8),
        ATTRIB( SDL_GL_BLUE_SIZE, 8),
        ATTRIB(SDL_GL_ALPHA_SIZE, 8),
        ATTRIB(SDL_GL_DEPTH_SIZE, 0),
        ATTRIB(SDL_GL_DOUBLEBUFFER, 1),
        ATTRIB(SDL_GL_ACCELERATED_VISUAL, 1),
        ATTRIB(SDL_GL_CONTEXT_MAJOR_VERSION, 4),
        ATTRIB(SDL_GL_CONTEXT_MINOR_VERSION, 3),
#ifdef USE_CORE_PROFILE
        ATTRIB(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE)
#else
        ATTRIB(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_COMPATIBILITY)
#endif
    };

    const size_t N = sizeof(attrs) / sizeof(attrs[0]);

    for (size_t i = 0; i < N; ++i) {
        if (SDL_GL_SetAttribute(attrs[i].attr, attrs[i].value) != 0) {
            f << "SDL_GL_SetAttribute() failed!\n";
        }
    }

    SDL_Window * window = SDL_CreateWindow("Meow", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1920, 1200, SDL_WINDOW_OPENGL);

    if (!window) {
        f << "SDL_CreateWindow() failed!\n";
    }

    SDL_GLContext context = SDL_GL_CreateContext(window);

    if (!context) {
        f << "SDL_GL_CreateContext() failed!\n";
    }

    for (size_t i = 0; i < N; ++i) {
        int val = 0;

        if (SDL_GL_GetAttribute(attrs[i].attr, &val) != 0) {
            f << "SDL_GL_GetAttribute(" << attrs[i].name << ") failed!\n";
            continue;
        }

        if (val != attrs[i].value) {
            f << "Unexpected attribute value!\n";
        }
    }

    if (glGetError() == GL_NO_ERROR) {
        f << "Done!\n";
    } else {
        f << "glGetError() recorded failure!\n";
    }

    SDL_GL_DeleteContext(context);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}

C:\Temp\gcc>g++ -Wall -Wextra -mwindows meow.cpp -o meow.exe -lopengl32 -lSDL2 -limm32 -lole32 -loleaut32 -luuid -lversion -lwinmm -lmingw32 -lSDL2main

C:\Temp\gcc>meow

C:\Temp\gcc>type output.txt
Using compatibility profile.
Done!

C:\Temp\gcc>g++ -DUSE_CORE_PROFILE -Wall -Wextra -mwindows meow.cpp -o meow.exe -lopengl32 -lSDL2 -limm32 -lole32 -loleaut32 -luuid -lversion -lwinmm -lmingw32 -lSDL2main

C:\Temp\gcc>meow

C:\Temp\gcc>type output.txt
Using core profile.
SDL_GL_GetAttribute(SDL_GL_RED_SIZE) failed!
SDL_GL_GetAttribute(SDL_GL_GREEN_SIZE) failed!
SDL_GL_GetAttribute(SDL_GL_BLUE_SIZE) failed!
SDL_GL_GetAttribute(SDL_GL_ALPHA_SIZE) failed!
SDL_GL_GetAttribute(SDL_GL_DEPTH_SIZE) failed!
Done!

The problem is in SDL_video.c, where SDL_GL_GetAttribute() calls glGetIntegerv() with GL_RED_BITS. As http://www.opengl.org/registry/doc/glspec43.compatibility.20130214.pdf explains in D.2.2 "Removed Features", page 790, this enum was removed:

"Context framebuffer size queries - RED_BITS, GREEN_BITS, BLUE_BITS, ALPHA_BITS, DEPTH_BITS, and STENCIL_BITS."

(STENCIL doesn't appear in my test because I'm not using it, but it is clearly also affected.)

The core-friendly way to query this information appears to be glGetFramebufferAttachmentParameteriv(), available since OpenGL 3.0: http://www.opengl.org/wiki/GLAPI/glGetFramebufferAttachmentParameter