Feature #8344
closed
libc ulwp walker should use CTF for uberdata offsets
100%
Description
At present, the ulwp (aka ulwps) walker in mdb uses the OFFSETOF() macro to locate the all_lwps pointer within the uberdata_t. Unfortunately, this member has changed offset at least once in recent history – from 0x295c to 0x29dc.
We should attempt to use the CTF which is invariably present in libc.so.1 to determine what this offset is, and only use the compile-time value as a fallback. As this module is Private, we should use mdb_ctf_offsetof() here.
Updated by Robert Mustacchi almost 6 years ago
For testing, Jason found a couple old cores that current mdb seems unhappy with (using ::uberdata just to illustrate that the built-in offsets are obviously wrong for this core):
[root@c1748f12-9915-67d4-a625-a1a41dd84898 ~]# mdb core.34733
mdb: failed to initialize //lib/libc_db.so.1: libthread_db call failed unexpectedly
mdb: warning: debugger will only be able to examine raw LWPs
Loading modules: [ libc.so.1 ld.so.1 ]
> ::uberdata
libc.so.1`_uberdata:
&link_lock &ld_lock &fork_lock
+0x0 0xfeefa1c0 0xfeefa200 0xfeefa240
&atfork_lock &callout_lock &tdb_hash_lock
+0xc0 0xfeefa280 0xfeefa2c0 0xfeefa2e0
...
ulwp_one all_lwps all_zombies
+0x2a78 <NULL> <NULL> 0xfeedfd3e
nthreads nzombies ndaemons pid
+0x2a84 -17957550 -17957534 -17957510 -17957497
...
> ::walk ulwp
>
With new libc.so:
[root@c1748f12-9915-67d4-a625-a1a41dd84898 ~]# mdb -L /home/build/smartos-live/proto/usr/lib/mdb/proc core.34733 mdb: failed to initialize //lib/libc_db.so.1: libthread_db call failed unexpectedly mdb: warning: debugger will only be able to examine raw LWPs Loading modules: [ libc.so.1 ld.so.1 ] > ::walk ulwp 0xfed42a40 > (other window -- verify it's using the new lib) [root@c1748f12-9915-67d4-a625-a1a41dd84898 ~]# pldd `pgrep mdb` 22647: mdb -L /home/build/smartos-live/proto/usr/lib/mdb/proc core.34733 /usr/bin/i86/mdb /lib/libumem.so.1 /usr/lib/libdisasm.so.1 /proc/52439/object/ufs.36.64.12234 /lib/libctf.so.1 /lib/libcurses.so.1 /usr/lib/libkvm.so.1 /lib/libproc.so.1 /lib/librtld_db.so.1 /lib/libelf.so.1 /usr/lib/libzonecfg.so.1 /lib/libxml2.so.2 /lib/libz.so.1 /lib/libm.so.2 /lib/libsocket.so.1 /lib/libnsl.so.1 /lib/libpthread.so.1 /usr/lib/libgcc_s.so.1 /lib/libuuid.so.1 /lib/libc_db.so.1 /home/build/smartos-live/proto/usr/lib/mdb/proc/libc.so /lib/libavl.so.1 /home/build/smartos-live/proto/usr/lib/mdb/proc/ld.so
A current system:
[root@c1748f12-9915-67d4-a625-a1a41dd84898 ~]# mdb -p 52439 Loading modules: [ libumem.so.1 libc.so.1 libuutil.so.1 libavl.so.1 libnvpair.so.1 ] > ::walk ulwp 0xfedf2a40 0xfe790240 0xfe790a40 0xfe791240 0xfe791a40 0xfe792240 0xfe793240 0xfe793a40 0xfe794240 0xfe794a40 0xfe795240 0xfe795a40 0xfe796240 0xfe796a40 0xfe797240 0xfe797a40 0xfe798240 0xfe798a40 0xfe799240 0xfe799a40 0xfe79a240 0xfe79aa40 0xfe79b240 0xfe79ba40 0xfe79c240 0xfe79ca40 0xfe79d240 0xfe79e240 > [root@c1748f12-9915-67d4-a625-a1a41dd84898 ~]# mdb -L /home/build/smartos-live/proto/usr/lib/mdb/proc -p 52439 Loading modules: [ libumem.so.1 libuutil.so.1 libavl.so.1 libnvpair.so.1 ] > ::load libc.so > ::walk ulwp 0xfedf2a40 0xfe790240 0xfe790a40 0xfe791240 0xfe791a40 0xfe792240 0xfe793240 0xfe793a40 0xfe794240 0xfe794a40 0xfe795240 0xfe795a40 0xfe796240 0xfe796a40 0xfe797240 0xfe797a40 0xfe798240 0xfe798a40 0xfe799240 0xfe799a40 0xfe79a240 0xfe79aa40 0xfe79b240 0xfe79ba40 0xfe79c240 0xfe79ca40 0xfe79d240 0xfe79e240 >
Also ran the same tests from a platform image built with the change with similar results (though no -L needed – as expected – for successful ::walk ulwp with same core files that don't work on current platform)
Updated by Electric Monk almost 6 years ago
- Status changed from New to Closed
git commit e0ee3ced1741d2c52b01a4527f8504cb24701b58
commit e0ee3ced1741d2c52b01a4527f8504cb24701b58
Author: Jason King <jason.king@joyent.com>
Date: 2017-06-22T18:49:43.000Z
8344 libc ulwp walker should use CTF for uberdata offsets
Reviewed by: Patrick Mooney <patrick.mooney@joyent.com>
Reviewed by: Hans Rosenfeld <hans.rosenfeld@joyent.com>
Reviewed by: Robert Mustacchi <rm@joyent.com>
Reviewed by: Toomas Soome <tsoome@me.com>
Reviewed by: Gordon Ross <gordon.w.ross@gmail.com>
Approved by: Richard Lowe <richlowe@richlowe.net>