uboot: play a bit, buildroot hello world start linking

README.adoc

@@ -9051,6 +9051,14 @@ I however see no joy on blobs. Buildroot does not seem to support EDK 2.
 
 Link on readme https://stackoverflow.com/questions/49348453/xen-on-qemu-with-arm64-architecture
 
+== U-Boot
+
+https://en.wikipedia.org/wiki/Das_U-Boot
+
+U-Boot is a popular bootloader.
+
+It can read disk filesystems, and Buildroot supports it, so we could in theory put it into memory, and let it find a kernel image from the root filesystem and boot that, but I didn't manage to get it working yet: https://stackoverflow.com/questions/58028789/how-to-boot-linux-aarch64-with-u-boot-with-buildroot-on-qemu
+
 == QEMU
 
 === Introduction to QEMU
@@ -12809,6 +12817,14 @@ git -C "$(./getvar buildroot_source_dir)" grep 'depends on BR2_TOOLCHAIN_USES_GL
 
 One "downside" of glibc is that it exercises much more kernel functionality on its more bloated pre-main init, which breaks user mode C hello worlds more often, see: xref:user-mode-simulation-with-glibc[xrefstyle=full]. I quote "downside" because glibc is actually exposing emulator bugs which we should actually go and fix.
 
+=== Buildroot hello world
+
+This repo doesn't do much more other than setting a bunch of Buildroot configurations and building it, and the minimal work you have to do to get QEMU to boot Buildroot from scratch is tiny if you want to quickly test Buildroot specifics, for example:
+
+* aarch64 https://stackoverflow.com/questions/47557262/how-to-download-the-torvalds-linux-kernel-master-recompile-it-and-boot-it-wi/49349237#49349237
+* arm https://stackoverflow.com/questions/38320066/how-to-run-linux-on-a-qemu-arm-versatile-machine/44099299#44099299
+* PPC <https://stackoverflow.com/questions/48021127/build-powerpc-kernel-and-boot-powerpc-kernel-on-qemu/49349262#49349262> just work commands for PPC, comment on how to replace kernel
+
 == Userland content
 
 This section contains userland content, such as <<c>>, <<cpp>> and <<posix>> examples.