[POWERPC] zImage: Cleanup and improve zImage entry point

This patch re-organises the way the zImage wrapper code is entered, to
allow more flexibility on platforms with unusual entry conditions.
After this patch, a platform .o file has two options:

1) It can define a _zimage_start, in which case the platform code gets
   control from the very beginning of execution.  In this case the
   platform code is responsible for relocating the zImage if necessary,
   clearing the BSS, performing any platform specific initialization, and
   finally calling start() to load and enter the kernel.

2) It can define platform_init().  In this case the generic crt0.S
   handles initial entry, and calls platform_init() before calling
   start().  The signature of platform_init() is changed, however, to
   take up to 5 parameters (in r3..r7) as they come from the platform's
   initial loader, instead of a fixed set of parameters based on OF's
   usage.

   When using the generic crt0.S, the platform .o can optionally
   supply a custom stack to use, using the BSS_STACK() macro.  If this
   is not supplied, the crt0.S will assume that the loader has
   supplied a usable stack.

In either case, the platform code communicates information to the
generic code (specifically, a PROM pointer for OF systems, and/or an
initrd image address supplied by the bootloader) via a global
structure "loader_info".

In addition the wrapper script is rearranged to ensure that the
platform .o is always linked first.  This means that platforms where
the zImage entry point is at a fixed address or offset, rather than
being encoded in the binary header can be supported using option (1).

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index 3628d868184424222bc03489ad095935da9a5f30..b1fc029e5ea76aff1a275034ed41136fe4a0830a 100644 (file)
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -40,11 +40,11 @@ zliblinuxheader := zlib.h zconf.h zutil.h
 $(addprefix $(obj)/,$(zlib) main.o): $(addprefix $(obj)/,$(zliblinuxheader)) \
                $(addprefix $(obj)/,$(zlibheader))
 
-src-wlib := string.S stdio.c main.c flatdevtree.c flatdevtree_misc.c \
+src-wlib := string.S crt0.S stdio.c main.c flatdevtree.c flatdevtree_misc.c \
                ns16550.c serial.c simple_alloc.c div64.S util.S \
                gunzip_util.c $(zlib)
 src-plat := of.c
-src-boot := crt0.S $(src-wlib) $(src-plat) empty.c
+src-boot := $(src-wlib) $(src-plat) empty.c
 
 src-boot := $(addprefix $(obj)/, $(src-boot))
 obj-boot := $(addsuffix .o, $(basename $(src-boot)))
@@ -97,7 +97,7 @@ $(obj)/wrapper.a: $(obj-wlib)
 
 hostprogs-y    := addnote addRamDisk hack-coff mktree
 
-extra-y                := $(obj)/crt0.o $(obj)/wrapper.a $(obj-plat) $(obj)/empty.o \
+extra-y                := $(obj)/wrapper.a $(obj-plat) $(obj)/empty.o \
                   $(obj)/zImage.lds $(obj)/zImage.coff.lds
 
 wrapper                :=$(srctree)/$(src)/wrapper

diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
index 70e65b13e0336fd86c02f3c602181be94c3ae3e0..3dc8d8f784998746693a1529e5085cce32eaf024 100644 (file)
--- a/arch/powerpc/boot/crt0.S
+++ b/arch/powerpc/boot/crt0.S
@@ -16,6 +16,7 @@
 _zimage_start_opd:
        .long   _zimage_start, 0, 0, 0
 
+       .weak   _zimage_start
        .globl  _zimage_start
 _zimage_start:
        /* Work out the offset between the address we were linked at
@@ -44,7 +45,7 @@ _zimage_start:
        addi    r9,r9,4
        bdnz    2b
 
-       /* Do a cache flush for our text, in case OF didn't */
+       /* Do a cache flush for our text, in case the loader didn't */
 3:     lis     r9,_start@ha
        addi    r9,r9,_start@l
        add     r9,r0,r9
@@ -59,6 +60,31 @@ _zimage_start:
        sync
        isync
 
-       mr      r6,r1
-       b       start
+       /* Clear the BSS */
+       lis     r9,__bss_start@ha
+       addi    r9,r9,__bss_start@l
+       lis     r8,_end@ha
+       addi    r8,r8,_end@l
+       li      r0,0
+5:     stw     r0,0(r9)
+       addi    r9,r9,4
+       cmplw   cr0,r9,r8
+       blt     5b
 
+       /* Possibly set up a custom stack */
+.weak  _platform_stack_top
+       lis     r8,_platform_stack_top@ha
+       addi    r8,r8,_platform_stack_top@l
+       cmpwi   r8,0
+       beq     6f
+       lwz     r1,0(r8)
+       li      r0,0
+       stwu    r0,-16(r1)      /* establish a stack frame */
+6:
+
+       /* Call platform_init() */
+       bl      platform_init
+
+       /* Call start */
+       mr      r3,r1
+       b       start

diff --git a/arch/powerpc/boot/main.c b/arch/powerpc/boot/main.c
index 05de6cfafeeb546f51aecd4e618a94e679783f6d..8a60e13777d793c4a4211f07220fb01f81062a0f 100644 (file)
--- a/arch/powerpc/boot/main.c
+++ b/arch/powerpc/boot/main.c
@@ -254,21 +254,15 @@ static void set_cmdline(char *buf)
 struct platform_ops platform_ops;
 struct dt_ops dt_ops;
 struct console_ops console_ops;
+struct loader_info loader_info;
 
-void start(unsigned long a1, unsigned long a2, void *promptr, void *sp)
+void start(void *sp)
 {
        struct addr_range vmlinux, initrd;
        kernel_entry_t kentry;
        char cmdline[COMMAND_LINE_SIZE];
        unsigned long ft_addr = 0;
 
-       memset(__bss_start, 0, _end - __bss_start);
-       memset(&platform_ops, 0, sizeof(platform_ops));
-       memset(&dt_ops, 0, sizeof(dt_ops));
-       memset(&console_ops, 0, sizeof(console_ops));
-
-       if (platform_init(promptr, _dtb_start, _dtb_end))
-               exit();
        if (console_ops.open && (console_ops.open() < 0))
                exit();
        if (platform_ops.fixups)
@@ -278,7 +272,8 @@ void start(unsigned long a1, unsigned long a2, void *promptr, void *sp)
               _start, sp);
 
        vmlinux = prep_kernel();
-       initrd = prep_initrd(vmlinux, a1, a2);
+       initrd = prep_initrd(vmlinux, loader_info.initrd_addr,
+                            loader_info.initrd_size);
 
        /* If cmdline came from zimage wrapper or if we can edit the one
         * in the dt, print it out and edit it, if possible.
@@ -298,7 +293,7 @@ void start(unsigned long a1, unsigned long a2, void *promptr, void *sp)
        if (ft_addr)
                printf(" flat tree at 0x%lx\n\r", ft_addr);
        else
-               printf(" using OF tree (promptr=%p)\n\r", promptr);
+               printf(" using OF tree (promptr=%p)\n\r", loader_info.promptr);
 
        if (console_ops.close)
                console_ops.close();
@@ -307,7 +302,8 @@ void start(unsigned long a1, unsigned long a2, void *promptr, void *sp)
        if (ft_addr)
                kentry(ft_addr, 0, NULL);
        else
-               kentry((unsigned long)initrd.addr, initrd.size, promptr);
+               kentry((unsigned long)initrd.addr, initrd.size,
+                      loader_info.promptr);
 
        /* console closed so printf below may not work */
        printf("Error: Linux kernel returned to zImage boot wrapper!\n\r");

diff --git a/arch/powerpc/boot/of.c b/arch/powerpc/boot/of.c
index 044f34770b9685633532bc716020e2cbe51a6ae0..c6f0d9701485cf8d5b5b3f90fbf13e5b72acb751 100644 (file)
--- a/arch/powerpc/boot/of.c
+++ b/arch/powerpc/boot/of.c
@@ -267,7 +267,7 @@ static void of_console_write(char *buf, int len)
        call_prom("write", 3, 1, of_stdout_handle, buf, len);
 }
 
-int platform_init(void *promptr, char *dt_blob_start, char *dt_blob_end)
+void platform_init(unsigned long a1, unsigned long a2, void *promptr)
 {
        platform_ops.image_hdr = of_image_hdr;
        platform_ops.malloc = of_try_claim;
@@ -282,5 +282,7 @@ int platform_init(void *promptr, char *dt_blob_start, char *dt_blob_end)
        console_ops.write = of_console_write;
 
        prom = (int (*)(void *))promptr;
-       return 0;
+       loader_info.promptr = promptr;
+       loader_info.initrd_addr = a1;
+       loader_info.initrd_size = a2;
 }

diff --git a/arch/powerpc/boot/ops.h b/arch/powerpc/boot/ops.h
index fa62ff223e70e9554777279419d5d47b46621195..cad4eee599fbf824c33b582936ff9f1502f881c0 100644 (file)
--- a/arch/powerpc/boot/ops.h
+++ b/arch/powerpc/boot/ops.h
@@ -59,7 +59,13 @@ struct serial_console_data {
        void            (*close)(void);
 };
 
-int platform_init(void *promptr, char *dt_blob_start, char *dt_blob_end);
+struct loader_info {
+       void *promptr;
+       unsigned long initrd_addr, initrd_size;
+};
+extern struct loader_info loader_info;
+
+void start(void *sp);
 int ft_init(void *dt_blob, unsigned int max_size, unsigned int max_find_device);
 int serial_console_init(void);
 int ns16550_console_init(void *devp, struct serial_console_data *scdp);
@@ -100,4 +106,8 @@ static inline void exit(void)
        for(;;);
 }
 
+#define BSS_STACK(size) \
+       static char _bss_stack[size]; \
+       void *_platform_stack_top = _bss_stack + sizeof(_bss_stack);
+
 #endif /* _PPC_BOOT_OPS_H_ */

diff --git a/arch/powerpc/boot/wrapper b/arch/powerpc/boot/wrapper
index 024e4d425c596b30fd9b31817d0dbc2bb0a4a990..157d8c89e1386915f85351f1db836aff494a2366 100755 (executable)
--- a/arch/powerpc/boot/wrapper
+++ b/arch/powerpc/boot/wrapper
@@ -191,7 +191,7 @@ fi
 
 if [ "$platform" != "miboot" ]; then
     ${CROSS}ld -m elf32ppc -T $lds -o "$ofile" \
-       $object/crt0.o $platformo $tmp $object/wrapper.a
+       $platformo $tmp $object/wrapper.a
     rm $tmp
 fi
 
@@ -201,7 +201,9 @@ pseries|chrp)
     $object/addnote "$ofile"
     ;;
 pmaccoff)
-    ${CROSS}objcopy -O aixcoff-rs6000 --set-start 0x500000 "$ofile"
+    entry=`objdump -f "$ofile" | grep '^start address ' | \
+       cut -d' ' -f3`
+    ${CROSS}objcopy -O aixcoff-rs6000 --set-start "$entry" "$ofile"
     $object/hack-coff "$ofile"
     ;;
 esac

diff --git a/arch/powerpc/boot/zImage.coff.lds.S b/arch/powerpc/boot/zImage.coff.lds.S
index a360905e54282b7908e55203d538dfb730746030..fe87a90ce7f1a606bba00f50597ac9677757598c 100644 (file)
--- a/arch/powerpc/boot/zImage.coff.lds.S
+++ b/arch/powerpc/boot/zImage.coff.lds.S
@@ -1,5 +1,6 @@
 OUTPUT_ARCH(powerpc:common)
-ENTRY(_start)
+ENTRY(_zimage_start_opd)
+EXTERN(_zimage_start_opd)
 SECTIONS
 {
   . = (5*1024*1024);

diff --git a/arch/powerpc/boot/zImage.lds.S b/arch/powerpc/boot/zImage.lds.S
index 4be3c6414b04d683ff015ff6cc2648da62fb0ee7..f6e380fdb388903a01394c1643f3a7b71ae2c455 100644 (file)
--- a/arch/powerpc/boot/zImage.lds.S
+++ b/arch/powerpc/boot/zImage.lds.S
@@ -1,5 +1,6 @@
 OUTPUT_ARCH(powerpc:common)
 ENTRY(_zimage_start)
+EXTERN(_zimage_start)
 SECTIONS
 {
   . = (4*1024*1024);