Question

I got a segfault when I tried to load a 771×768 image.

Tried with a 24×24 and 768×768 image and they worked, no problem.

Is this expected? Why wouldn’t it just fail gracefully with a GL Error?

The segmentation fault occurs in the glTexImage2D call. I am loading a PPM binary file so it is packed 24 bits per pixel. This odd number combined with an odd dimension probably produces a not-4-byte (or even 2-byte) aligned structure (and referencing outside of my exactly enough allocated buffer may be the cause of the error but gdb does not show me a memory address (which I could use to find out if this is what causes it)).

glTexImage2D(GL_TEXTURE_2D, 0, 3, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, dataptr);
// in this specific case of failure, width = 771, height = 768,
// dataptr contains 1776384 bytes of binary RGB image data (771*768*3 = 1776384)

Answer 1

This odd number combined with an odd dimension probably produces a not-4-byte (or even 2-byte) aligned structure (and referencing outside of my exactly enough allocated buffer may be the cause of the error

This is likely the cause. Luckily you can set the alignment OpenGL uses reading pixel data. Right before calling glTexImage…(…) do

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
glPixelStorei(GL_UNPACK_SKIP_PIXELS, 0);
glPixelStorei(GL_UNPACK_SKIP_ROWS, 0);