On 11/27/23 22:52, David Hildenbrand wrote:
On 26.11.23 14:56, Oleg Nesterov wrote:
On 11/26, Rong Tao wrote:
then the PR_GET_VMA interface should be provided accordingly,
which is necessary, as the userspace program usually wants to know what
VMA name it has configured for the anonymous page.
I don't really understand the use-case for PR_GET_VMA ...
Can't we simply read "/proc/PID/maps" and just have that information
from there?
Thank you, David.
The relationship between PR_GET_VMA and /proc/PID/maps is like the
relationship between
PR_GET_NAME and /proc/PID/comm. Obviously, both methods can obtain the
corresponding
name. However, prctl(2) can be obtained directly from the code level,
while reading proc is not
so convenient and efficient. Moreover, reading proc is more like bash
command line, rather
than C code.
Also, I don't understand the exact use case, that should be clarified
-- especially, why the existing way is insufficient.
For use-case, in fact, I now want to develop a user-mode patch tool and
need to map the patch file to the target
process(Use ptrace(2) and pread/pwrite("/proc/self/mem")). I initially
used shared files
00400000-00401000 r--p 00000000 08:00 241933181
/home/sda/git-repos/upatch/tests/hello/hello
00401000-00402000 r-xp 00001000 08:00 241933181
/home/sda/git-repos/upatch/tests/hello/hello
00402000-00403000 r--p 00002000 08:00 241933181
/home/sda/git-repos/upatch/tests/hello/hello
00403000-00404000 r--p 00002000 08:00 241933181
/home/sda/git-repos/upatch/tests/hello/hello
00404000-00405000 rw-p 00003000 08:00 241933181
/home/sda/git-repos/upatch/tests/hello/hello
01136000-01157000 rw-p 00000000 00:00 0 [heap]
7f21472c0000-7f21472c2000 rw-p 00000000 00:00 0
7f21472c2000-7f21472e8000 r--p 00000000 103:03 3705
/usr/lib64/libc.so.6
7f21472e8000-7f2147448000 r-xp 00026000 103:03 3705
/usr/lib64/libc.so.6
7f2147448000-7f2147496000 r--p 00186000 103:03 3705
/usr/lib64/libc.so.6
7f2147496000-7f214749a000 r--p 001d3000 103:03 3705
/usr/lib64/libc.so.6
7f214749a000-7f214749c000 rw-p 001d7000 103:03 3705
/usr/lib64/libc.so.6
7f214749c000-7f21474a6000 rw-p 00000000 00:00 0
7f21474be000-7f21474bf000 rwxs 00000000 00:27 7794
/tmp/upatch/62984/map_files/patch-FKSYTp <<
7f21474bf000-7f21474c0000 rwxs 00000000 00:27 7793
/tmp/upatch/62984/map_files/patch-KFaQNU <<
7f21474c0000-7f21474c1000 r--p 00000000 103:03 3702
/usr/lib64/ld-linux-x86-64.so.2
7f21474c1000-7f21474e8000 r-xp 00001000 103:03 3702
/usr/lib64/ld-linux-x86-64.so.2
7f21474e8000-7f21474f2000 r--p 00028000 103:03 3702
/usr/lib64/ld-linux-x86-64.so.2
7f21474f2000-7f21474f4000 r--p 00031000 103:03 3702
/usr/lib64/ld-linux-x86-64.so.2
7f21474f4000-7f21474f6000 rw-p 00033000 103:03 3702
/usr/lib64/ld-linux-x86-64.so.2
7ffec158b000-7ffec15ad000 rw-p 00000000 00:00 0 [stack]
7ffec15cf000-7ffec15d3000 r--p 00000000 00:00 0 [vvar]
7ffec15d3000-7ffec15d5000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall]
However, this is obviously not the best approach, I want to use
anonymous pages instead,
7f21474be000-7f21474bf000 rwxp 00000000 00:27 7794 [anon:patch1]
7f21474bf000-7f21474c0000 rwxp 00000000 00:27 7793 [anon:patch2]
I hope to use the address to directly obtain the vma name, which is
"patch1". This is very convenient
in the program without parsing /proc/PID/maps in the source code.
Thanks again.
Rong Tao
