[PATCH] fix multiboot loading if load_end_addr == 0

[PATCH] fix multiboot loading if load_end_addr == 0

[Scott Moser]

The previous code did not treat the case where load_end_addr was 0
specially.  The multiboot specification says the following:
 * load_end_addr
   Contains the physical address of the end of the data segment.
   (load_end_addr - load_addr) specifies how much data to load. This
   implies that the text and data segments must be consecutive in the
   OS image; this is true for existing a.out executable formats. If
   this field is zero, the boot loader assumes that the text and data
   segments occupy the whole OS image file.

This was raised initially as launchpad bug
https://bugs.launchpad.net/qemu/+bug/957622

diff --git a/hw/multiboot.c b/hw/multiboot.c
index b4484a3..b1e04c5 100644
--- a/hw/multiboot.c
+++ b/hw/multiboot.c
@@ -202,10 +202,16 @@ int load_multiboot(void *fw_cfg,
         uint32_t mh_bss_end_addr = ldl_p(header+i+24);
         mh_load_addr = ldl_p(header+i+16);
         uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
-        uint32_t mb_load_size = mh_load_end_addr - mh_load_addr;
-
+        uint32_t mb_load_size = 0;
         mh_entry_addr = ldl_p(header+i+28);
-        mb_kernel_size = mh_bss_end_addr - mh_load_addr;
+
+        if (mh_load_end_addr) {
+            mb_kernel_size = mh_bss_end_addr - mh_load_addr;
+            mb_load_size = mh_load_end_addr - mh_load_addr;
+        } else {
+            mb_kernel_size = kernel_file_size - mb_kernel_text_offset;
+            mb_load_size = mb_kernel_size;
+        }

         /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.
         uint32_t mh_mode_type = ldl_p(header+i+32);

Re: [PATCH] fix multiboot loading if load_end_addr == 0

[Jan Kiszka]

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On 2012-03-17 05:08, Scott Moser wrote:
> The previous code did not treat the case where load_end_addr was 0
> specially.  The multiboot specification says the following:
>  * load_end_addr
>    Contains the physical address of the end of the data segment.
>    (load_end_addr - load_addr) specifies how much data to load. This
>    implies that the text and data segments must be consecutive in the
>    OS image; this is true for existing a.out executable formats. If
>    this field is zero, the boot loader assumes that the text and data
>    segments occupy the whole OS image file.
> 
> This was raised initially as launchpad bug
> https://bugs.launchpad.net/qemu/+bug/957622
> 
> diff --git a/hw/multiboot.c b/hw/multiboot.c
> index b4484a3..b1e04c5 100644
> --- a/hw/multiboot.c
> +++ b/hw/multiboot.c
> @@ -202,10 +202,16 @@ int load_multiboot(void *fw_cfg,
>          uint32_t mh_bss_end_addr = ldl_p(header+i+24);
>          mh_load_addr = ldl_p(header+i+16);
>          uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
> -        uint32_t mb_load_size = mh_load_end_addr - mh_load_addr;
> -
> +        uint32_t mb_load_size = 0;
>          mh_entry_addr = ldl_p(header+i+28);
> -        mb_kernel_size = mh_bss_end_addr - mh_load_addr;
> +
> +        if (mh_load_end_addr) {
> +            mb_kernel_size = mh_bss_end_addr - mh_load_addr;
> +            mb_load_size = mh_load_end_addr - mh_load_addr;
> +        } else {
> +            mb_kernel_size = kernel_file_size - mb_kernel_text_offset;
> +            mb_load_size = mb_kernel_size;
> +        }
> 
>          /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.
>          uint32_t mh_mode_type = ldl_p(header+i+32);

Almost everything should go to upstream directly these days, including
this fix.

Jan


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