[OpenBIOS] [PATCH] a.out header copy

[Olivier Danet]

On 07/02/2014 19:24, Mark Cave-Ayland wrote:
> On 05/02/14 22:51, Olivier Danet wrote:
>
>> Here is the beginning of the NextSTEP bootloader :
>>
>> Dump of assembler code from 0x4000 to 0x4100:
>> => 0x00004000: tst %o0
>> 0x00004004: be 0x404c
>> 0x00004008: nop
>> 0x0000400c: mov %o0, %g7
>> 0x00004010: sethi %hi(0x4000), %o1
>> 0x00004014: mov %o1, %o1 ! 0x4000
>> 0x00004018: sub %o1, 0x1c, %o2
>> 0x0000401c: ld [ %o2 ], %o2 <<<<<<< HERE : $O2=*(0x4000-0x1C)
>> 0x00004020: add %o2, %o1, %o2
>> 0x00004024: sethi %hi(0x5800), %g1
>> 0x00004028: st %g7, [ %g1 + 0x110 ] ! 0x5910
>> 0x0000402c: ld [ %o0 + 4 ], %o4
>> 0x00004030: mov %o1, %l0
>> 0x00004034: add %o1, 0x20, %l1
>> 0x00004038: call 0x4088
>> 0x0000403c: sub %o2, %o1, %l2
>> 0x00004040: tst %o4
>> 0x00004044: be 0x404c
>> 0x00004048: nop
>> 0x0000404c: save %o1, -96, %sp
>> 0x00004050: call 0x432c
>>
>> Addresses are absolute. This code is directly copied from the ISO's
>> sector 1
>>
>> It accesses the a.out header very early (which helped _a lot_
>> to find the bug) to get the a_text field, which is the lenght of the
>> TEXT segment.
>> Sun's OpenBOOT copies the whole header at 0x3FE0, not the .a_text only.
>>
>> Are there SunOS version using a.out ?
>>
>> Of course, we could add #ifdef CONFIG_SPARC32 fences.
>
> Hi Olivier,
>
> Thanks for this. Checking the source here I see that only SPARC32 and 
> SPARC64 define CONFIG_LOADER_AOUT, so it's a fairly limited audience.
>
> I wonder if we need to control whether things are non-compliant or not 
> through the CONFIG_QEMU switch?
>
> Regardless, for this case I think just add a #define at the top of the 
> file that controls whether or not to load the header beneath 
> load-base. As a minor nit, would it be possible to rework the patch so 
> that it optionally loads the header first before the payload? At the 
> moment, it loads the payload and then seeks back to read in the header 
> which seems slightly counter-intuitive.
>
>
> ATB,
>
> Mark.
Right, there is no need to seek backwards to pick the a.out header on 
disk, as it is already loaded in memory.

Simpler :

Index: libopenbios/aout_load.c
===================================================================
--- libopenbios/aout_load.c    (révision 1257)
+++ libopenbios/aout_load.c    (copie de travail)
@@ -9,6 +9,9 @@
  #ifdef CONFIG_SPARC64
  #define CONFIG_SPARC64_PAGE_SIZE_8KB
  #endif
+#ifdef CONFIG_SPARC32
+#define AOUT_HEADER_COPY
+#endif

  #include "libopenbios/sys_info.h"
  #include "libopenbios/bindings.h"
@@ -140,6 +143,10 @@
          }
      }

+#ifdef AOUT_HEADER_COPY
+    // Copy the a.out header just before the start
+    memcpy((char *)(start-0x20), &ehdr, 0x20);
+#endif
      debug("Loaded %lu bytes\n", size);
      debug("entry point is %#lx\n", start);

===================================================================

Olivier