From: Ben Pfaff <blp@cs.stanford.edu>
Date: Thu, 2 Sep 2004 21:50:25 +0000 (+0000)
Subject: Make linking of start.S less brittle.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=commitdiff_plain;h=dfb64e1c2e16f8e5183de565bd4819d875379cee

Make linking of start.S less brittle.
---

diff --git a/src/Makefile.inc b/src/Makefile.inc
index 982b5e8..bab467a 100644
--- a/src/Makefile.inc
+++ b/src/Makefile.inc
@@ -15,8 +15,7 @@ CFLAGS = -g -O3 -MMD -msoft-float $(WARNINGS) $(INCLUDES) $(DEFINES)
 ASFLAGS = -Wa,--gstabs+ $(INCLUDES) $(DEFINES)
 
 # Core kernel.
-THREADS_SRC  = start.S		# Must be linked first.
-THREADS_SRC += init.c		# Main program.
+THREADS_SRC  = init.c		# Main program.
 THREADS_SRC += thread.c		# Thread management core.
 THREADS_SRC += switch.S		# Thread switch routine.
 THREADS_SRC += interrupt.c	# Interrupt core.
@@ -25,6 +24,7 @@ THREADS_SRC += synch.c		# Synchronization.
 THREADS_SRC += paging.c		# Page tables.
 THREADS_SRC += palloc.c		# Page allocator.
 THREADS_SRC += malloc.c		# Subpage allocator.
+THREADS_SRC += start.S		# Startup code.
 
 # Device driver code.
 DEVICES_SRC  = timer.c		# Timer device.
diff --git a/src/threads/kernel.lds.S b/src/threads/kernel.lds.S
index b911b29..ce5d23d 100644
--- a/src/threads/kernel.lds.S
+++ b/src/threads/kernel.lds.S
@@ -11,7 +11,7 @@ SECTIONS
   _start = .;
 
   /* Kernel starts with code, followed by read-only data and writable data. */
-  .text : { *(.text) } = 0x9090
+  .text : { *(.start) *(.text) } = 0x9090
   .rodata : { *(.rodata) *(.rodata.*) }
   .data : { *(.data) }
 
diff --git a/src/threads/start.S b/src/threads/start.S
index 5862479..df63f85 100644
--- a/src/threads/start.S
+++ b/src/threads/start.S
@@ -1,8 +1,12 @@
-# This module gets linked first, so that the kernel entry point
-# is the very beginning of its binary image.  All we need to do is
-# jump to the real entry point.
+#### The loader needs to have some way to know the kernel's entry
+#### point, that is, the address to which it should jump to start the
+#### kernel.  We handle this by writing the linker script kernel.lds.S
+#### so that this module appears at the very beginning of the kernel
+#### image, and then using that as the entry point.
 
 .globl start
+.section .start
+
 start:	call main
 
 	# If main returns, spin.