At 03/01/2012 03:04 PM, HATAYAMA Daisuke Wrote:
> From: Wen Congyang <we...@cn.fujitsu.com>
> Subject: [RFC][PATCH 09/14 v7] introduce a new monitor command 'dump' to dump
> guest's memory
> Date: Thu, 01 Mar 2012 10:51:42 +0800
>
>> + /*
>> + * calculate phdr_num
>> + *
>> + * the type of phdr->num is uint16_t, so we should avoid overflow
>> + */
>> + s->phdr_num = 1; /* PT_NOTE */
>> + if (s->list.num > (1 << 16) - 2) {
>> + s->phdr_num = (1 << 16) - 1;
>> + } else {
>> + s->phdr_num += s->list.num;
>> + }
>> +
>> + return s;
>> +}
>
> Though e_phnum is uint16_t at default, there's extension up to
> uint32_t. Look at relatively new manual page. This is from FC14's.
>
> e_phnum This member holds the number of entries in the
> program header table. Thus the product of
> e_phentsize and e_phnum gives the table's size
> in bytes. If a file has no program header,
> e_phnum holds the value zero.
>
> If the number of entries in the program header
> table is larger than or equal to PN_XNUM
> (0xffff), this member holds PN_XNUM (0xffff) and
> the real number of entries in the program header
> table is held in the sh_info member of the
> initial entry in section header table.
> Otherwise, the sh_info member of the initial
> entry contains the value zero.
>
> PN_XNUM This is defined as 0xffff, the largest
> number e_phnum can have, specifying
> where the actual number of program
> headers is assigned.
Good news.
>
> Recent kernel, gdb and tools in binutils supports this. But crash
> doesn't, so you need to fix this.
I think it can be easily fixed.
>
> I'm interested in the number of program headers at worst
> case. According to Intel Programming Guide 3A, Table 4-1. shows
> physical-address width on IA-32e is up to 52 and linear-address width
> is 48. Can the number exceed this limit in theory? Also how many
> program headers are created typically?
In my test, the guest has 512M memory, and it contains about 1000~2000 program
headers.
In theory, if the guest has 2^52 memory, the number can still exceed this limit.
Tha maxnium number is 2^52/2^12
Thanks
Wen Congyang
>
> Thanks.
> HATAYAMA, Daisuke
>
>
