Re: [RFC] binutils/objdump: Fix disassemble with huge elf sections

[Alan Modra <amodra at gmail dot com>]

On Wed, Jul 12, 2017 at 11:00:20AM +0530, Ravi Bangoria wrote:
> When elf section size is beyond unsigned int max value, objdump fails
> to disassemble from that section. Ex on PowerPC,
> 
>   $ objdump -h /proc/kcore
>     Idx  Name   Size       VMA
>       4  load2  100000000  c000000000000000
> 
> Here, size of load2 section is 0x100000000. Also note that, 0xc00....
> address range is kernel space for PowerPC. Now let's try to disassemble
> do_sys_open() using /proc/kcore.
> 
>   $ cat /proc/kallsyms | grep -A1 -w do_sys_open
>     c00000000036c000 T do_sys_open
>     c00000000036c2d0 T SyS_open
> 
> Before patch:
> 
>   $ objdump -d --start-address=0xc00000000036c000 --stop-address=0xc00000000036c2d0 /proc/kcore
>     /proc/kcore:    file format elf64-powerpcle
> 
>     Disassembly of section load2:
> 
>     c00000000036c000 <load2+0x36c000>:
>     c00000000036c000:    Address 0xc00000000036c000 is out of bounds.
> 
> Fix this by changing type of 'buffer_length' from unsigned int to
> size_t. After patch:
> 
>   $ objdump -d --start-address=0xc00000000036c000 --stop-address=0xc00000000036c2d0 /proc/kcore
>     /proc/kcore:    file format elf64-powerpcle
> 
>     Disassembly of section load2:
> 
>     c00000000036c000 <load2+0x36c000>:
>     c00000000036c000: fc 00 4c 3c     addis   r2,r12,252
>     c00000000036c004: 00 53 42 38     addi    r2,r2,21248
>     c00000000036c008: a6 02 08 7c     mflr    r0
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
> ---
>  include/dis-asm.h | 2 +-
>  opcodes/dis-buf.c | 8 ++++----
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/dis-asm.h b/include/dis-asm.h
> index 9b42514..4ff8bc9 100644
> --- a/include/dis-asm.h
> +++ b/include/dis-asm.h
> @@ -158,7 +158,7 @@ typedef struct disassemble_info
>    /* These are for buffer_read_memory.  */
>    bfd_byte *buffer;
>    bfd_vma buffer_vma;
> -  unsigned int buffer_length;
> +  size_t buffer_length;
>  
>    /* This variable may be set by the instruction decoder.  It suggests
>        the number of bytes objdump should display on a single line.  If
> diff --git a/opcodes/dis-buf.c b/opcodes/dis-buf.c
> index 061bc44..2027f08 100644
> --- a/opcodes/dis-buf.c
> +++ b/opcodes/dis-buf.c
> @@ -31,10 +31,10 @@ buffer_read_memory (bfd_vma memaddr,
>  		    unsigned int length,
>  		    struct disassemble_info *info)
>  {
> -  unsigned int opb = info->octets_per_byte;
> -  unsigned int end_addr_offset = length / opb;
> -  unsigned int max_addr_offset = info->buffer_length / opb;
> -  unsigned int octets = (memaddr - info->buffer_vma) * opb;
> +  unsigned long opb = info->octets_per_byte;
> +  unsigned long end_addr_offset = length / opb;
> +  unsigned long max_addr_offset = info->buffer_length / opb;
> +  unsigned long octets = (memaddr - info->buffer_vma) * opb;
>  
>    if (memaddr < info->buffer_vma
>        || memaddr - info->buffer_vma > max_addr_offset

Thanks for the patch fixing some of binutils horrible old code!  I
think the dis-asm.h change is fine, but please leave opb as an
unsigned int and change the others to size_t in dis-buf.c.  We also
need ChangeLog entries for binutils patches.

-- 
Alan Modra
Australia Development Lab, IBM