From: Aruna Hewapathirane <aruna.hewapathirane@gmail.com>
To: kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Virtual To Physical Address Translation
Date: Tue, 14 May 2019 08:20:50 -0400 [thread overview]
Message-ID: <CAFSeFg_4soNbm3VJxv8++ANrT4ALpsDCfmzd9kKZavVG=h+OHg@mail.gmail.com> (raw)
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Hi,
I am trying to wrap my head around the virtual to physical memory address
translation. For example let's say I want to locate the sys_call_table.
objdump and vmlinux shows me this:
aruna@debian:~/linux-5.1.1$ objdump -t vmlinux | grep -i sys_call_table
ffffffff81c001c0 g O .rodata 0000000000001120 sys_call_table
ffffffff81c01600 g O .rodata 0000000000000d60 ia32_sys_call_table
and System.map shows me this:
aruna@debian:~/linux-5.1.1$ cat System.map | grep -i sys_call_table
ffffffff81c001c0 R sys_call_table
ffffffff81c01600 R ia32_sys_call_table
So addresses match.
And gdb shows me this:
aruna@debian:~/linux-5.1.1$ gdb vmlinux
GNU gdb (Debian 7.7.1+dfsg-5) 7.7.1
Reading symbols from vmlinux...done.
(gdb) p sys_call_table
$1 = {0xffffffff812317a0 <__x64_sys_read>,
0xffffffff812318b0 <__x64_sys_write>, 0xffffffff8122d980
<__x64_sys_open>,
0xffffffff8122bc40 <__x64_sys_close>,
0xffffffff81236220 <__x64_sys_newstat>,
0xffffffff812363e0 <__x64_sys_newfstat>,
<snip>
Now if you take the address given by objdump and System.map which is
0xffffffff81c001c0
and ask gdb to show you I get:
(gdb) x 0xffffffff81c001c0
0xffffffff81c001c0 <sys_call_table>: 0x812317a0
My question is HOW is the address 0xffffffff81c001c0 translated to
0x812317a0 ? I am reading up on page tables and page offsets just can't yet
fully understand how it is done. A example that
breaks down the process step by step would really help.
Thanks - Aruna
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next reply other threads:[~2019-05-14 12:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-14 12:20 Aruna Hewapathirane [this message]
2019-05-15 9:33 ` Virtual To Physical Address Translation Amit Kumar
2019-05-15 9:39 ` Amit Kumar
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