Enabling CONFIG_FB_BCM2708 doesn't solve this issue since there's a failure when loading that driver.
vcdbg works as expected on Raspbian. Building a stock Raspberry Pi3 image using the raspberrypi3_defconfig provided by buildroot also results in the same failure of loading the module, so it's probably a buildroot issue.
Which makes it quiet difficult to debug/troubleshoot the boot process. Seems to be caused by the
/dev/fb0device not being the bcm2708 framebuffer. Apparentlyvcdbgreads(!) from the framebuffer to get some of the information it needs, see https://www.raspberrypi.org/forums/viewtopic.php?p=1266903&sid=440ae36c24cbc9fcec1b15963e57ff0c#p1266903Enabling
CONFIG_FB_BCM2708doesn't solve this issue since there's a failure when loading that driver.vcdbgworks as expected on Raspbian. Building a stock Raspberry Pi3 image using theraspberrypi3_defconfigprovided by buildroot also results in the same failure of loading the module, so it's probably a buildroot issue.