Arm: do a 4th linking pass if necessary

The .rodata growth between 1st and 2nd linking passes may affect the
number of stubs the linker wants to insert, which in turn affects the
number of symbols. If symbol table sizes change after the 2nd linking
pass, insert another one before the final one. (As a comment in Linux puts
it, "In theory it's possible this results in even more stubs, but
unlikely.")

To use the $(compare-symbol-tables) macro in a shell "if", it needs
slightly adjusting (and then wrapping to be run in a sub-shell).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
Acked-by: Bertrand Marquis <bertrand.marquis@arm.com>

xen/arch/arm/Makefile

@@ -99,9 +99,21 @@ $(TARGET)-syms: $(objtree)/prelink.o $(obj)/xen.lds
 		| $(objtree)/tools/symbols $(all_symbols) --sysv --sort \
 		> $(dot-target).2.S
 	$(MAKE) $(build)=$(@D) $(dot-target).2.o
-	$(call compare-symbol-tables, $(dot-target).1.o, $(dot-target).2.o)
+	if ! { $(call compare-symbol-tables, $(dot-target).1.o, $(dot-target).2.o) >/dev/null; }; \
+	then \
+		set -e; \
+		$(LD) $(XEN_LDFLAGS) -T $(obj)/xen.lds $< $(build_id_linker) \
+		    $(dot-target).2.o -o $(dot-target).2; \
+		$(NM) -pa --format=sysv $(dot-target).2 \
+			| $(objtree)/tools/symbols $(all_symbols) --sysv --sort \
+			> $(dot-target).3.S; \
+		$(MAKE) $(build)=$(@D) $(dot-target).3.o; \
+		$(call compare-symbol-tables, $(dot-target).2.o, $(dot-target).3.o); \
+	else \
+		ln -sf $(dot-target).2.o $(dot-target).3.o; \
+	fi
 	$(LD) $(XEN_LDFLAGS) -T $(obj)/xen.lds $< $(build_id_linker) \
-	    $(dot-target).2.o -o $@
+	    $(dot-target).3.o -o $@
 	$(NM) -pa --format=sysv $@ \
 		| $(objtree)/tools/symbols --all-symbols --xensyms --sysv --sort \
 		> $@.map

xen/scripts/Kbuild.include

@@ -65,7 +65,7 @@ define compare-symbol-tables
     $(OBJDUMP) -t $(@D)/.cst.$$$$ > $(1).sym; \
     ln -f $(2) $(@D)/.cst.$$$$; \
     $(OBJDUMP) -t $(@D)/.cst.$$$$ > $(2).sym; \
-    rm -f $(@D)/.cst.$$$$
+    rm -f $(@D)/.cst.$$$$; \
     diff -u $(1).sym $(2).sym
 endef