#systemtap on 2020-10-08 — irc logs at freenode.irclog.whitequark.org

2015-11-12 23:18 fche changed the topic of #systemtap to: http://sourceware.org/systemtap; email systemtap@sourceware.org if answers here not timely, conversations may be logged

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15:06 <modem> @define container_of(ptr, type, member) %( @cast(@ptr - @offsetof(@type, @member), @type)

15:06 <modem> %)

15:06 <modem> i added that in my script

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15:07 <modem> semantic error: unresolved function (similar: error, log, HZ, assert, bio_op): identifier 'container_of' at 8897c1b1a1795cab23d5ac13e4e23bf0b5f4e0c6.stp:73:10 source: inode = container_of ($head, "inode", "i_rcu");

15:07 <modem> nevertheless I keep having issue in my script

15:07 <modem> any advices on how to properly use container_of ? Thanks

15:08 <modem> Systemtap translator/driver (version 4.0/0.176, Debian version 4.0-1)

15:08 <modem> maybe that's my issue

15:08 <modem> let's upgrade to latest, sorry for buzzing

15:10 <fche> @container_of is how you refer to macros

15:10 <modem> hah

15:11 <fche> you might need @module_container_of if the @cast needs a module

15:13 <modem> semantic error: 'struct inode' (./include/linux/fs.h:593) is being accessed instead of a member such as '->__i_nlink': operator '@cast'

15:14 <modem> does it want to force me using a dereference instead of assigning a variabe with type casted ?

15:14 <fche> what's the complete script?

15:15 <modem> inode = @container_of (register("rdi"), "inode", i_rcu);

15:15 <modem> only that

15:16 <modem> struggling from a struct rcu_head *head in some rcu_callback

15:16 <fche> could you fpaste the more complete script so I can try it here?

15:17 <modem> sure, thanks!

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15:20 <modem> https://pastebin.com/LyHisRN3

15:20 <modem> thanks you1

15:20 <modem> thanks you!

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15:21 <modem> note register("rdi") is supposed to be $head but I tried that because it wasn't working

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15:29 <modem> ok got it working! Thanks

15:29 <fche> great

15:29 <modem> i missed &

15:30 <modem> inode = &@container_of ($head, "inode", i_rcu);

15:30 <modem> tysm

15:30 <fche> ah yes

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22:08 <modem> fche:

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23:24 <modem> i think i have a problem with an .return probe

23:25 <modem> apparently the subroutine (main routine) has not been executed when the .return probe run

23:25 <modem> I tried probing one function above in the calling hierarchy

23:25 <modem> and it still hasn't run my main routine

23:26 <modem> i looked at the assembly and it seems it's triggered from running return probe in function returning void

23:26 <modem> the last opcode is a jmp to the subroutine

23:26 <modem> i guess that systemtap is adding its int3 on the last instruction

23:27 <modem> hence the return probe run before the last instruction has been executed

23:27 <modem> in my case before the main subroutine has been executed

23:38 <modem> no no no my bad

23:38 <modem> that's not my issue

23:38 <modem> i have been badly testing per-cpu variable

23:39 <modem> i suspect the probe handler might run on another cpu