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video: Don't rely on memcpy undefined behavior

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The C specification states that passing a size of 0 to functions like memcpy is valid, but even if the size is 0 and the function is essentially a no-op, the result when passing any invalid pointers is considered undefined behavior. Don't rely on undefined behavior when copying the display or mode lists.
This commit is contained in:
Frank Praznik 2023-02-02 13:43:43 -05:00 committed by Sam Lantinga
parent 166afebcad
commit 47cdb532f1
1 changed files with 18 additions and 13 deletions
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31
src/video/SDL_video.c
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@ -634,17 +634,19 @@ SDL_DisplayID SDL_AddVideoDisplay(const SDL_VideoDisplay *display, SDL_bool send
if (displays) {
int i;
/* The display list may contain self-referential pointers to the desktop mode. */
SDL_memcpy(displays, _this->displays, _this->num_displays * sizeof(*displays));
for (i = 0; i < _this->num_displays; ++i) {
if (displays[i].current_mode == &_this->displays[i].desktop_mode) {
displays[i].current_mode = &displays[i].desktop_mode;
if (_this->displays) {
/* The display list may contain self-referential pointers to the desktop mode. */
SDL_memcpy(displays, _this->displays, _this->num_displays * sizeof(*displays));
for (i = 0; i < _this->num_displays; ++i) {
if (displays[i].current_mode == &_this->displays[i].desktop_mode) {
displays[i].current_mode = &displays[i].desktop_mode;
}
}
SDL_free(_this->displays);
}
SDL_free(_this->displays);
_this->displays = displays;
id = _this->next_object_id++;
new_display = &displays[_this->num_displays++];
@ -954,15 +956,18 @@ SDL_bool SDL_AddFullscreenDisplayMode(SDL_VideoDisplay *display, const SDL_Displ
return SDL_FALSE;
}
/* Copy the list and update the current mode pointer, if necessary. */
SDL_memcpy(modes, display->fullscreen_modes, nmodes * sizeof(*modes));
for (i = 0; i < nmodes; ++i) {
if (display->current_mode == &display->fullscreen_modes[i]) {
display->current_mode = &modes[i];
if (display->fullscreen_modes) {
/* Copy the list and update the current mode pointer, if necessary. */
SDL_memcpy(modes, display->fullscreen_modes, nmodes * sizeof(*modes));
for (i = 0; i < nmodes; ++i) {
if (display->current_mode == &display->fullscreen_modes[i]) {
display->current_mode = &modes[i];
}
}
SDL_free(display->fullscreen_modes);
}
SDL_free(display->fullscreen_modes);
display->fullscreen_modes = modes;
display->max_fullscreen_modes += 32;
}