[Skiboot] [RFC PATCH 4/5] skiboot.lds.S: introduce PAGE_SIZE, use it to lay out sections

[Nicholas Piggin]

Separate code, data, read-only data, and other significant sections
with PAGE_SIZE alignment. This enables memory protection for these
sections with a later patch.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 include/config.h |  3 +++
 skiboot.lds.S    | 20 +++++++++++++-------
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/include/config.h b/include/config.h
index d7a64b712..2877007fb 100644
--- a/include/config.h
+++ b/include/config.h
@@ -4,6 +4,9 @@
 #ifndef __CONFIG_H
 #define __CONFIG_H
 
+/* Alignment to which skiboot lays out memory. */
+#define PAGE_SIZE	0x10000
+
 #define HAVE_TYPEOF			1
 #define HAVE_BUILTIN_TYPES_COMPATIBLE_P	1
 
diff --git a/skiboot.lds.S b/skiboot.lds.S
index 64efa7765..0fc0e7c8f 100644
--- a/skiboot.lds.S
+++ b/skiboot.lds.S
@@ -75,6 +75,7 @@ SECTIONS
 	}
 
 	_head_end = .;
+	. = ALIGN(PAGE_SIZE);
 
 	/*
 	 * The following sections are read-write at runtime. We need
@@ -107,14 +108,14 @@ SECTIONS
 	}
 
 	/* ...and back to RO */
-
-	. = ALIGN(0x10);
+	. = ALIGN(PAGE_SIZE);
 	_stext = .;
  	.text : {
 		*(.text*)
 		*(.sfpr .glink)
 	}
 	_etext = .;
+	. = ALIGN(PAGE_SIZE);
 
 	.rodata : {
 		__rodata_start = .;
@@ -177,6 +178,7 @@ SECTIONS
 		*(.rela*)
 		__rela_dyn_end = .;
 	}
+
 	.hash          : { *(.hash)   }
 	.gnu.hash      : { *(.gnu.hash) }
 	.gnu.version   : { *(.gnu.version) }
@@ -196,22 +198,26 @@ SECTIONS
 	 */
 	_romem_end = .;
 
+	. = ALIGN(PAGE_SIZE);
+
+	_sdata = .;
 	.data : {
 		/*
 		 * A couple of things that need to be 4K aligned and
 		 * to reside in their own pages for the sake of TCE
 		 * mappings
 		 */
-		. = ALIGN(0x1000);
+		. = ALIGN(PAGE_SIZE);
 		*(.data.memcons);
-		. = ALIGN(0x10000);
+		. = ALIGN(PAGE_SIZE);
 		*(.data.boot_trace);
-		. = ALIGN(0x10000);
+		. = ALIGN(PAGE_SIZE);
 		*(.data*)
 		*(.force.data)
 		*(.toc1)
 		*(.branch_lt)
 	}
+	_edata = .;
 
 	/* We locate the BSS at 4M to leave room for the symbol map */
 	. = 0x400000;
@@ -221,7 +227,7 @@ SECTIONS
 		*(.dynbss)
 		*(.bss*)
 	}
-	. = ALIGN(0x10000);
+	. = ALIGN(PAGE_SIZE);
 	_ebss = .;
 	_end = .;
 
@@ -230,7 +236,7 @@ SECTIONS
 	DEBUG_SECTIONS
 
 	/* Optional kernel image */
-       . = ALIGN(0x10000);
+       . = ALIGN(PAGE_SIZE);
        .builtin_kernel : {
 		__builtin_kernel_start = .;
 		KEEP(*(.builtin_kernel))
-- 
2.23.0