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Bug 1652740

Summary: can't resolve some kernel function parameters; partial-inlining, debuginfo problem
Product: Red Hat Enterprise Linux 8 Reporter: Frank Ch. Eigler <fche>
Component: systemtapAssignee: Frank Ch. Eigler <fche>
systemtap sub component: system-version QA Contact: qe-baseos-tools-bugs
Status: CLOSED CURRENTRELEASE Docs Contact:
Severity: unspecified    
Priority: unspecified CC: dsmith, lberk, mcermak, mjw
Version: 8.0Keywords: Triaged
Target Milestone: rcFlags: pm-rhel: mirror+
Target Release: 8.0   
Hardware: x86_64   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2020-04-22 12:22:16 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 1169184, 1173076, 1785287    
Bug Blocks:    

Description Frank Ch. Eigler 2018-11-22 18:38:36 UTC 
kernel 4.18.0-28.el8 + debuginfo
systemtap 4.0-something

% stap -p4 -e 'probe module("*").function("rpc_call_sync") { println($clnt) }'
location attribute for 'clnt' [man error::dwarf]: identifier '$clnt' at <input>:1:55
        dieoffset: 0x2d10e from /usr/lib/debug/lib/modules/4.18.0-28.el8.x86_64/kernel/net/sunrpc/sunrpc.ko.debug
        function: rpc_call_sync at net/sunrpc/clnt.c:1064:5
        source: probe module("*").function("rpc_call_sync") { println($clnt) }
Comment 1 Frank Ch. Eigler 2018-11-22 18:45:06 UTC 
In this case, .part. inlining seems responsible; one copy has parameters, another one doesn't.

% stap -vv -p4 -e 'probe module("sunrpc").function("rpc_call_sync") { println($msg) }'

probe rpc_call_sync@net/sunrpc/clnt.c:1064 module=sunrpc reloc=.text pc=0x12ba0
probe rpc_call_sync@net/sunrpc/clnt.c:1064 module=sunrpc reloc=.text pc=0x118a0
semantic error: while processing probe module("sunrpc").function("rpc_call_sync@net/sunrpc/clnt.c:1064") from: module("sunrpc").function("rpc_call_sync")
   thrown from: elaborate.cxx:5832
semantic error: failed to retrieve location attribute for 'msg' [man error::dwarf]: identifier '$msg' at <input>:1:60
        dieoffset: 0x2d109 from /usr/lib/debug/lib/modules/4.18.0-28.el8.x86_64/kernel/net/sunrpc/sunrpc.ko.debug
        function: rpc_call_sync at net/sunrpc/clnt.c:1064:5
   thrown from: dwflpp.cxx:3993
        source: probe module("sunrpc").function("rpc_call_sync") { println($msg) }
Comment 2 Martin Cermak 2018-11-22 20:17:26 UTC 
Observable on x86_64, ppc64le, s390x.  The aarch64 platform seems unaffected.
Comment 3 Frank Ch. Eigler 2018-11-27 15:38:11 UTC 
blocked by absence of relevant debuginfo from gcc
Comment 4 Martin Cermak 2018-12-10 17:00:52 UTC 
Another similar problem is the unreachability of function parameters in the main ppc64le fork-routine _do_fork():

=======
 8.0 Server ppc64le # nl -ba /root/rpmbuild/BUILD/kernel-4.18.0-50.el8/linux-4.18.0-50.el8.ppc64le/kernel/fork.c | sed '2088,2102!d'
  2088  }
  2089  
  2090  /*
  2091   *  Ok, this is the main fork-routine.
  2092   *
  2093   * It copies the process, and if successful kick-starts
  2094   * it and waits for it to finish using the VM if required.
  2095   */
  2096  long _do_fork(unsigned long clone_flags,
  2097                unsigned long stack_start,
  2098                unsigned long stack_size,
  2099                int __user *parent_tidptr,
  2100                int __user *child_tidptr,
  2101                unsigned long tls)
  2102  {
 8.0 Server ppc64le #
=======

No parameters are available there:

=======
 8.0 Server ppc64le # stap -L 'kernel.function("_do_fork")'
kernel.function("_do_fork@kernel/fork.c:2096")
 8.0 Server ppc64le #
=======

This is a regression compared to rhel7.
Comment 6 Frank Ch. Eigler 2020-04-22 12:22:16 UTC 
verified with rhel 8.2 binaries