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p53ud0ny1 >
How can i control the execution flow of some function? e.g. I want to intercept function foobar() and make it immediatly return value x.
11:32
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p53ud0ny1 >
I know how to probe the function, but how can i modify it's behavoir?
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prerna >
hi, I'm getting this error when I compile my systemtap script :
11:35
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prerna >
Makefile:619: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong not supported by compiler
11:35
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prerna >
Makefile:619: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong not supported by compiler
11:35
<
prerna >
Makefile:619: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong not supported by compiler
11:35
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prerna >
Makefile:619: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong not supported by compiler
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11:35
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prerna >
Cannot use CONFIG_CC_STACKPROTECTOR_STRONG : -fstack_protector_strong not supported
11:35
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prerna >
(sorry for the multiple copy)
11:36
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prerna >
Is there a way for me to turn it off ?
11:36
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prerna >
btw, my script is just running userspace probe:
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prerna >
stap -k -vve 'probe process("/usr/libexec/qemu-kvm").mark("scsi_req_parsed") {print("Hi");} '
11:41
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lorddoskias1 >
p53ud0ny1: apparently this is not possible :) at least in kernel mode ;0
11:42
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lorddoskias1 >
prerna: try upgrading your compiler?
11:43
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prerna >
lorddoskias1, that isn't an option :) I was wondering if I could introduce a new flag that said "-Wnofstack-protector-strong" or somesuch
11:44
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lorddoskias1 >
funny
11:44
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lorddoskias1 >
i can't find any reference to fstack-protector-strong in current systemtap source
11:45
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prerna >
so I am unable to understand how this flag got picked
11:45
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lorddoskias1 >
maybe the process it's probing is compiled with this flag? e.g. qemu-vkm?
11:45
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lorddoskias1 >
objdump -s --section .comment /path/binary
11:45
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lorddoskias1 >
what does this show?
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11:47
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lorddoskias1 >
right, this just shows the gcc version
11:48
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lorddoskias1 >
so CONFIG_CC_STACKPROTECTOR_STRONG comes from your kernel config
11:48
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prerna >
hmm, but this is a userspace probe script
11:49
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prerna >
that was another thing -- systematic refused to process my script until I installed kernel-headers/devel/debuginfo.. and the script in question needed none of that
11:49
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prerna >
or did it ?
11:49
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prerna >
I mean, do userspace probes have any dependence on kernel-devel ?
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lorddoskias1 >
ops, got too eager with ctrl+w ;D
11:52
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lorddoskias1 >
as such in order to probe a userspace process you do have to compile a kernel module
11:52
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prerna >
hmm, that explains
11:53
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lorddoskias1 >
i have never dealt with uspace probing
11:54
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prerna >
so I installed another gcc under /opt/rh/devtoolset-3/ , modified PATH so that this was picked , but systemtap keeps giving me the same error
11:55
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lorddoskias1 >
i had the same problem :)
11:55
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prerna >
lorddoskias1, thanks, but you've been very helpful :)
11:55
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lorddoskias1 >
so what you have to do is
11:55
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lorddoskias1 >
stap -BCC=/path/to/dev/tool/set
11:55
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lorddoskias1 >
or rather /path/to/devtoolset/gcc
11:55
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prerna >
wow thanks,trying
11:57
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prerna >
I got another unrelated error, but naps, this helps !
11:57
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prerna >
thanks a tonne'
11:57
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prerna >
s/naps/nps
11:59
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lorddoskias1 >
i only knew this, since i had to also use the devtoolset rathen than the default compiler
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p53ud0ny1 >
lorddoskias1: Thanks. How about just modifying data at the kernel level? e.g. Changing a functions paramaters at a particular line.
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lorddoskias1 >
p53ud0ny1: you could potentially do that, depending on the visibility of the data in the debug symbols
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fche >
p53ud0ny1, # stap -g -e 'probe kernel.function("foo") { $param = 5 }' is the general pattern
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