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[PATCH, v5] ieee1275: Include a.out header in assembly of sparc64 boot l


From: John Paul Adrian Glaubitz
Subject: [PATCH, v5] ieee1275: Include a.out header in assembly of sparc64 boot loader
Date: Tue, 26 Mar 2019 10:40:50 +0100

Recent versions of binutils dropped support for the a.out and COFF
formats on sparc64 targets. Since the boot loader on sparc64 is
supposed to be an a.out binary and the a.out header entries are
rather simple to calculate in our case, we just write the header
ourselves instead of relying on external tools to do that.

Signed-off-by: John Paul Adrian Glaubitz <address@hidden>
---
v2:
- fix grammar in long description
v3:
- fix formatting in assembly code
- update comment in boot loader for consistency
v4:
- add comments to explain offset adjustments and a.out header fields
v5:
- explicitly pass '-O binary' in sparc64_ieee1275_objcopyflags to force binary 
output
- avoid redundant comments in grub-core/Makefile.core.def
- slightly reformat grub-core/Makefile.core.def for better readability

 grub-core/Makefile.core.def            | 16 +++++++++++----
 grub-core/boot/sparc64/ieee1275/boot.S | 27 +++++++++++++++++++++++---
 include/grub/sparc64/ieee1275/boot.h   |  3 +--
 3 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 43ed42191..cda8ea34c 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -425,8 +425,14 @@ image = {
   i386_qemu_ldflags = 
'$(TARGET_IMG_BASE_LDOPT),$(GRUB_BOOT_MACHINE_LINK_ADDR)';
   i386_qemu_ccasflags = 
'-DGRUB_BOOT_MACHINE_LINK_ADDR=$(GRUB_BOOT_MACHINE_LINK_ADDR)';
 
-  sparc64_ieee1275_objcopyflags = '-O a.out-sunos-big';
-  sparc64_ieee1275_ldflags = ' -Wl,-Ttext=0x4000';
+  /* The entry point for a.out binaries on sparc64 starts
+     at 0x4000. Since we are writing the 32 bytes long a.out
+     header in the assembly code ourselves, we need to tell
+     the linker to adjust the start of the text segment to
+     0x4000 - 0x20 = 0x3fe0.
+   */
+  sparc64_ieee1275_ldflags = ' -Wl,-Ttext=0x3fe0';
+  sparc64_ieee1275_objcopyflags = '-O binary';
 
   objcopyflags = '-O binary';
   enable = i386_pc;
@@ -455,8 +461,10 @@ image = {
   i386_pc_ldflags = '$(TARGET_IMG_BASE_LDOPT),0x7C00';
 
   sparc64_ieee1275 = boot/sparc64/ieee1275/boot.S;
-  sparc64_ieee1275_objcopyflags = '-O a.out-sunos-big';
-  sparc64_ieee1275_ldflags = ' -Wl,-Ttext=0x4000';
+
+  /* See comment for sparc64_ieee1275_ldflags above */
+  sparc64_ieee1275_ldflags = ' -Wl,-Ttext=0x3fe0';
+  sparc64_ieee1275_objcopyflags = '-O binary';
   sparc64_ieee1275_cppflags = '-DCDBOOT=1';
 
   objcopyflags = '-O binary';
diff --git a/grub-core/boot/sparc64/ieee1275/boot.S 
b/grub-core/boot/sparc64/ieee1275/boot.S
index 9ea9b4e06..ed3aec464 100644
--- a/grub-core/boot/sparc64/ieee1275/boot.S
+++ b/grub-core/boot/sparc64/ieee1275/boot.S
@@ -21,6 +21,23 @@
 
        .text
        .align  4
+       /* We're writing the a.out header ourselves as newer
+        * upstream versions of binutils no longer support
+        * the a.out format on sparc64.
+        *
+        * The boot loader fits into 512 bytes with 32 bytes
+        * used for the a.out header, hence the text segment
+        * size is 512 - 32. There is no data segment and no
+        * code relocation, thus those fields remain zero.
+        */
+       .word   0x1030107                        /* magic number */
+       .word   512 - GRUB_BOOT_AOUT_HEADER_SIZE /* size of text segment */
+       .word   0                                /* size of initialized data */
+       .word   0                                /* size of uninitialized data 
*/
+       .word   0                                /* size of symbol table || 
checksum */
+       .word   _start                           /* entry point */
+       .word   0                                /* size of text relocation */
+       .word   0                                /* size of data relocation */
        .globl  _start
 _start:
        /* OF CIF entry point arrives in %o4 */
@@ -40,10 +57,14 @@ pic_base:
         *
         * After loading in that block we will execute it by jumping to the
         * load address plus the size of the prepended A.OUT header (32 bytes).
+        *
+        * Since this assembly code includes the 32 bytes long a.out header,
+        * we need to move the actual code entry point forward by the size
+        * of the a.out header, i.e. += GRUB_BOOT_AOUT_HEADER_SIZE.
         */
-       .org GRUB_BOOT_MACHINE_BOOT_DEVPATH
+       .org GRUB_BOOT_MACHINE_BOOT_DEVPATH + GRUB_BOOT_AOUT_HEADER_SIZE
 boot_path:
-       .org GRUB_BOOT_MACHINE_KERNEL_BYTE
+       .org GRUB_BOOT_MACHINE_KERNEL_BYTE + GRUB_BOOT_AOUT_HEADER_SIZE
 boot_path_end:
 kernel_byte:           .xword (2 << 9)
 kernel_address:                .word  GRUB_BOOT_MACHINE_KERNEL_ADDR
@@ -52,7 +73,7 @@ kernel_address:               .word  
GRUB_BOOT_MACHINE_KERNEL_ADDR
 #define boot_path_end (_start + 1024)
 #include <grub/offsets.h>
 
-       .org 8
+       .org 8 + GRUB_BOOT_AOUT_HEADER_SIZE
 kernel_byte:           .xword (2 << 9)
 kernel_size:           .word  512
 kernel_address:                .word  GRUB_BOOT_SPARC64_IEEE1275_IMAGE_ADDRESS
diff --git a/include/grub/sparc64/ieee1275/boot.h 
b/include/grub/sparc64/ieee1275/boot.h
index 02d53f28e..cc5a941e3 100644
--- a/include/grub/sparc64/ieee1275/boot.h
+++ b/include/grub/sparc64/ieee1275/boot.h
@@ -46,8 +46,7 @@
 
 #define GRUB_BOOT_MACHINE_KERNEL_BYTE 0x80
 
-#define GRUB_BOOT_MACHINE_CODE_END \
-       (0x1fc - GRUB_BOOT_AOUT_HEADER_SIZE)
+#define GRUB_BOOT_MACHINE_CODE_END 0x1fc
 
 #define GRUB_BOOT_MACHINE_KERNEL_ADDR 0x4200
 
-- 
2.20.1




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