ppc.tmpl: clarify comments, fix yaboot.conf for Apple systems

So there's actually two copies of yaboot on a PPC image, and they each
use different config files:

  ppc/chrp/yaboot --> /etc/yaboot.conf
  ppc/mac/yaboot  --> /ppc/ppc{32,64}/yaboot.conf

So we need two copies of yaboot.conf - one in each place - to
boot properly (or all three if we're making hybrid images). Whee!

The comments should now make this more clear for future reference.

share/ppc.tmpl

@@ -11,21 +11,27 @@ WRAPPER_DATA="usr/"+libdir+"/kernel-wrapper"
 
 bitsizes = set()
 prepboot = ""
+rootarg = "root=live:CDLABEL=%s" % udev(isolabel)
 %>
 
 mkdir ${LIVEDIR}
 install ${runtime_img} ${LIVEDIR}/squashfs.img
 
-## install bootloaders
+## install bootloaders.
+## NOTE: there's two different bootloader setups here:
+##   ppc/chrp: for normal PPC systems. needs 'addnote' run on yaboot.
+##             uses /etc/yaboot.conf, as is the default.
+##   ppc/mac: for PowerMacs. no 'addnote' (it breaks some Macs!)
+##            ofboot.b picks one of /ppc/ppc{32,64}/yaboot.conf for yaboot,
+##            thus automatically booting the correct kernel for the machine.
 mkdir ${BOOTDIR}
-## basic ppc stuff
+## boot stuff for normal (CHRP/PREP) PPC systems
 install ${configdir}/bootinfo.txt ${BOOTDIR}
 install boot/efika.forth ${BOOTDIR}
-## boot dir for CHRP systems
 mkdir ${BOOTDIR}/chrp
 install usr/lib/yaboot/yaboot ${BOOTDIR}/chrp
 runcmd ${inroot}/usr/lib/yaboot/addnote ${outroot}/${BOOTDIR}/chrp/yaboot
-## boot dir for PowerMacs
+## special boot dir for PowerMacs
 mkdir ${MACDIR}
 install usr/lib/yaboot/yaboot ${MACDIR}
 install ${configdir}/ofboot.b ${MACDIR}
@@ -47,9 +53,12 @@ install ${configdir}/ofboot.b ${MACDIR}
     installkernel images-${kernel.arch} ${kernel.path} ${KERNELDIR}/vmlinuz
     installinitrd images-${kernel.arch} ${kernel.initrd.path} ${KERNELDIR}/initrd.img
 
-    ## install bootloader config
+    ## install arch-specific bootloader config
     install ${configdir}/yaboot.conf.in  ${KERNELDIR}/yaboot.conf
     replace @BITS@    ${bits}            ${KERNELDIR}/yaboot.conf
+    replace @PRODUCT@ ${product.name}    ${KERNELDIR}/yaboot.conf
+    replace @VERSION@ ${product.version} ${KERNELDIR}/yaboot.conf
+    replace @ROOT@    "${rootarg}"       ${KERNELDIR}/yaboot.conf
 
     ## kernel-wrapper magic that makes the netboot combined ppc{32,64}.img
     runcmd ${inroot}/${WRAPPER} -p of \
@@ -65,21 +74,19 @@ install ${configdir}/ofboot.b ${MACDIR}
     %endif
 %endfor
 
-## copy correct yaboot.conf into /etc
+## choose correct yaboot.conf
 mkdir etc
 %if len(bitsizes) == 2:
-    ## hybrid - use the magic hybrid config
+    ## both kernels means hybrid - use the magic hybrid config
     install ${configdir}/yaboot.conf.3264  etc/yaboot.conf
+    replace @PRODUCT@ ${product.name}      etc/yaboot.conf
+    replace @VERSION@ ${product.version}   etc/yaboot.conf
+    replace @ROOT@    "${rootarg}"         etc/yaboot.conf
 %else:
-    ## single arch - use the yaboot.conf we created above
+    ## single arch - use the arch-specific yaboot.conf from above
     copy ${KERNELDIR}/yaboot.conf etc/yaboot.conf
 %endif
 
-## configure bootloader
-replace @PRODUCT@ ${product.name}      etc/yaboot.conf
-replace @VERSION@ ${product.version}   etc/yaboot.conf
-replace @ROOT@ 'root=live:CDLABEL=${isolabel|udev}' etc/yaboot.conf
-
 ## make boot.iso
 runcmd mkisofs -o ${outroot}/images/boot.iso -chrp-boot -U \
         ${prepboot} -part -hfs -T -r -l -J \
@@ -93,9 +100,6 @@ runcmd mkisofs -o ${outroot}/images/boot.iso -chrp-boot -U \
         ${NETBOOTDIR}=${outroot}/${NETBOOTDIR} \
         ${LIVEDIR}=${outroot}/${LIVEDIR}
 
-%if len(bitsizes) == 2:
+%for kernel in kernels:
-    treeinfo images-ppc   boot.iso images/boot.iso
-    treeinfo images-ppc64 boot.iso images/boot.iso
-%else:
     treeinfo images-${kernel.arch} boot.iso images/boot.iso
-%endif
+%endfor