[Bug runtime/21020] reorganize argument passing from java probes

["penguin-kernel at i-love dot sakura dot ne dot jp" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=21020

--- Comment #2 from Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> ---
Thank you for the patch. Let me confirm again.

As of systemtap-3.0-7.el7 , it is possible to access java.lang.String argument
because $arg1 in method2 points to a valid address.

--------------------------------------------------------------------------------
# stap --compatible=3.0 -e 'probe
java("Test1").class("Test1").method("method1(int)") { printf("Hooked method1()
with arg = %d\n", $arg1); }
probe java("Test1").class("Test1").method("method2(String)") { printf("Hooked
method2() with arg = %s\n", user_string($arg1)); }
probe java("Test1").class("Test1").method("method3") { printf("Hooked
method3()\n"); }' -c 'java Test1'
100
Hello
Test1@73549af8
Setting org.jboss.byteman.transform.all=true
100
Hello
Test1@73549af8
Hooked method1() with arg = 100
Hooked method2() with arg = Hello
Hooked method3()
--------------------------------------------------------------------------------

If I built correctly from git source, as of commit f8bc2a5eb3e91ce7
"PR21020: reorganize data passing abi for java method parameters",
it is no longer possible to access java.lang.String argument using
--compatible=3.0 option because $arg1 in method2 points to NULL.
Is this what you meant?

--------------------------------------------------------------------------------
# stap --compatible=3.1 -e 'probe
java("Test1").class("Test1").method("method1(int)") { printf("Hooked method1()
with arg = %s\n", arg1); }
probe java("Test1").class("Test1").method("method2(String)") { printf("Hooked
method2() with arg = %s\n", arg1); }
probe java("Test1").class("Test1").method("method3(Test1)") { printf("Hooked
method3() with arg = %s\n", arg1); }' -c 'java Test1'
100
Hello
Test1@73549af8
Setting org.jboss.byteman.transform.all=true
100
Hello
Test1@73549af8
Hooked method1() with arg = 100
Hooked method2() with arg = Hello
Hooked method3() with arg = Test1@73549af8
--------------------------------------------------------------------------------
# stap --compatible=3.0 -e 'probe
java("Test1").class("Test1").method("method1(int)") { printf("Hooked method1()
with arg = %d\n", $arg1); }
probe java("Test1").class("Test1").method("method2(String)") { printf("Hooked
method2() with arg = %d\n", $arg1); }
probe java("Test1").class("Test1").method("method3(Test1)") { printf("Hooked
method3() with arg = %d\n", $arg1); }' -c 'java Test1'
100
Hello
Test1@73549af8
Setting org.jboss.byteman.transform.all=true
100
Hello
Test1@73549af8
Hooked method1() with arg = 100
Hooked method2() with arg = 0
Hooked method3() with arg = 0
--------------------------------------------------------------------------------

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