baremetal: fix heap and stack position in preparation for CLI arguments

README.adoc

@@ -19482,6 +19482,27 @@ It is not possible to call those C functions from the examples that don't use a
 
 For this reason, we tend to create examples with bootloaders, as it is easier to write them portably.
 
+=== Baremetal linker script
+
+For things to work in baremetal, we often have to layout memory in specific ways.
+
+Notably, since we start with <<arm-paging,paging>> disabled, there are more constraints on where memory can or cannot go.
+
+Especially for C programs, this memory layout is specified by a "linker script", which is present at: link:baremetal/link.ld[]
+
+Note how our linker script also exposes some symbols to C:
+
+....
+lkmc_heap_low = .;
+lkmc_heap_top = .;
+....
+
+Those for example are required to implement `malloc` in Newlib. We can play with those variables more explicitly with link:baremetal/linker_variables.c[]:
+
+....
+./run --arch aarch64 --baremetal baremetal/linker_variables.c
+....
+
 === Semihosting
 
 Semihosting is a publicly documented interface specified by ARM Holdings that allows us to do some magic operations very useful in development.