arm: clean up v7 and v8 linker scripts for bss_start/end

commit 3ebd1cbc49 ("arm: make __bss_start and __bss_end__ compiler-generated")
and
commit f84a7b8f54 ("ARM: Fix __bss_start and __bss_end in linker scripts")
were moving the bss_start/end on c generated variables that were
injected in their own sections. The reason was that we needed relative
relocations for position independent code and linker bugs back then
prevented us from doing so [0].

However, the linker documentation pages states that symbols that are
defined within a section definition will create a relocatable type with
the value being a fixed offset from the base of a section [1].
So let's start cleaning this up starting with the bss_start and bss_end
variables. Convert them into symbols within the .bss section definition.

[0] binutils commit 6b3b0ab89663 ("Make linker assigned symbol dynamic only for shared object")
[1] https://sourceware.org/binutils/docs/ld/Expression-Section.html

Tested-by: Caleb Connolly <caleb.connolly@linaro.org> # Qualcomm sdm845
Tested-by: Sam Edwards <CFSworks@gmail.com> # Binary output identical
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

arch/arm/cpu/armv8/u-boot-spl.lds

@@ -63,18 +63,11 @@ SECTIONS
 
 	_image_binary_end = .;
 
-	.bss_start (NOLOAD) : {
-		. = ALIGN(8);
-		KEEP(*(.__bss_start));
-	} >.sdram
-
-	.bss (NOLOAD) : {
+	.bss : {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-	} >.sdram
-
-	.bss_end (NOLOAD) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	} >.sdram
 
 	/DISCARD/ : { *(.rela*) }
@@ -89,3 +82,6 @@ SECTIONS
 #include "linux-kernel-image-header-vars.h"
 #endif
 }
+
+ASSERT(ADDR(.bss) % 8 == 0, \
+       ".bss must be 8-byte aligned");

arch/arm/cpu/armv8/u-boot.lds

@@ -149,19 +149,11 @@ SECTIONS
 
 	_end = .;
 
-	. = ALIGN(8);
-
-	.bss_start : {
-		KEEP(*(.__bss_start));
-	}
-
-	.bss : {
+	.bss ALIGN(8): {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-	}
-
-	.bss_end : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	}
 
 	/DISCARD/ : { *(.dynsym) }

arch/arm/cpu/u-boot.lds

@@ -207,23 +207,15 @@ SECTIONS
 	}
 
 /*
- * Compiler-generated __bss_start and __bss_end, see arch/arm/lib/bss.c
- * __bss_base and __bss_limit are for linker only (overlay ordering)
+ * These sections occupy the same memory, but their lifetimes do
+ * not overlap: U-Boot initializes .bss only after applying dynamic
+ * relocations and therefore after it doesn't need .rel.dyn any more.
  */
-
-	.bss_start __rel_dyn_start (OVERLAY) : {
-		KEEP(*(.__bss_start));
-		__bss_base = .;
-	}
-
-	.bss __bss_base (OVERLAY) : {
+	.bss ADDR(.rel.dyn) (OVERLAY): {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(4);
-		 __bss_limit = .;
-	}
-
-	.bss_end __bss_limit (OVERLAY) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(4);
+		__bss_end = .;
 	}
 
 	.dynsym _image_binary_end : { *(.dynsym) }

arch/arm/lib/sections.c

@@ -19,8 +19,6 @@
  * aliasing warnings.
  */
 
-char __bss_start[0] __section(".__bss_start");
-char __bss_end[0] __section(".__bss_end");
 char __image_copy_start[0] __section(".__image_copy_start");
 char __image_copy_end[0] __section(".__image_copy_end");
 char __rel_dyn_start[0] __section(".__rel_dyn_start");

arch/arm/mach-rockchip/u-boot-tpl-v8.lds

@@ -56,18 +56,11 @@ SECTIONS
 
 	_image_binary_end = .;
 
-	.bss_start (NOLOAD) : {
-		. = ALIGN(8);
-		KEEP(*(.__bss_start));
-	}
-
-	.bss (NOLOAD) : {
+	.bss ALIGN(8) : {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-	}
-
-	.bss_end (NOLOAD) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	}
 
 	/DISCARD/ : { *(.dynsym) }

arch/arm/mach-zynq/u-boot.lds

@@ -103,23 +103,15 @@ SECTIONS
 	_image_binary_end = .;
 
 /*
- * Compiler-generated __bss_start and __bss_end, see arch/arm/lib/bss.c
- * __bss_base and __bss_limit are for linker only (overlay ordering)
+ * These sections occupy the same memory, but their lifetimes do
+ * not overlap: U-Boot initializes .bss only after applying dynamic
+ * relocations and therefore after it doesn't need .rel.dyn any more.
  */
-
-	.bss_start __rel_dyn_start (OVERLAY) : {
-		KEEP(*(.__bss_start));
-		__bss_base = .;
-	}
-
-	.bss __bss_base (OVERLAY) : {
+	.bss ADDR(.rel.dyn) (OVERLAY): {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-		 __bss_limit = .;
-	}
-
-	.bss_end __bss_limit (OVERLAY) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	}
 
 	/*