https://bugs.kde.org/show_bug.cgi?id=419562
Bug ID: 419562
Summary: PR_SET_PTRACER error with Ubuntu on WSL
Product: valgrind
Version: unspecified
Platform: MS Windows
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: jsew...@acm.org
Reporter: e...@ozhiker.com
Target Milestone: ---
Created attachment 127224
--> https://bugs.kde.org/attachment.cgi?id=127224&action=edit
Possible fix by falling back to alternate PR_SET_PTRACER call
SUMMARY
When running Ubuntu 18.04 on Windows-Subsystem-for-Linux (WSL),
I have noticed the following error during every run of Valgrind:
error calling PR_SET_PTRACER, vgdb might block
STEPS TO REPRODUCE
1. Use Ubuntu 18.04 on WSL
2. Build Valgrind from git
./autogen.sh && ./configure && make -j8 --quiet check
3. Run valgrind against any program:
VALGRIND_LIB=./.in_place VALGRIND_LIB_INNER=./.in_place/
./coregrind/valgrind pwd
OBSERVED RESULT
error calling PR_SET_PTRACER, vgdb might block
EXPECTED RESULT
no error
SOFTWARE/OS VERSIONS
Windows: 10 (1909) 10.0.18363.720
Linux: Ubuntu 18.04 on WSL
Valgrind: 3.16.0.GIT
ADDITIONAL INFORMATION
This is caused by a bug in noted in the following stack overflow:
https://stackoverflow.com/questions/57206233/valgrind-showing-error-calling-pr-set-ptracer-vgdb-might-block
It was logged with Microsoft as:
https://github.com/microsoft/WSL/issues/3053
It has apparently been fixed in WSL build 17723:
https://docs.microsoft.com/en-us/windows/wsl/release-notes#build-17723-fast
However it seems that it has not yet reached Windows Update (despite my PC
being at build 18363)
The error comes from VG_(set_ptracer)() in coregrind/m_gdbserver/remote-utils.c
It appears that the following call fails:
ret = VG_(prctl) (PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
But if the following alternate line is enabled, the call succeeds:
ret = VG_(prctl) (PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
I believe we could work around this by just failing-over from the first prctl
to the second.
I will submit a patch which does that.
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