> On the subject line, the ToT lldb (see code around
CommandObjectThread.cpp:1230) sets the breakpoint on the first exact
matching line of 'line-number' or the closest line number > 'line-number'
i.e. the best match.
> And along with that, starting from the above exact/best matching line
number index in the line table, the breakpoints are also being set on every
other line number available in the line table in the current function
scope. This latter part, I believe, is incorrect.
Why do you think this is incorrect?
The requirements for "thread until <line number>" are:
a) If any code contributed by <line number> is executed before leaving the
b) If you end up leaving the function w/o triggering (a), then stop
Understood and no concerns on this.
Correct or incorrect should be determined by how well the implementation
fits those requirements.
There isn't currently a reliable indication from the debug information or
line tables that "line N will always be entered starting with the block at
0x123". So you can't tell without doing control flow analysis, which if
any of the separate entries in the line table for the same line will get
hit in the course of executing the function. So the safest thing to do is
to set breakpoints on them all.
From the above, I understand that we have to do this when the debug line
table has more than one entry for a particular source line. And this is
what I referred to as "machine code for one single source line is scattered
across" in my previous mail. Thanks for sharing why we had to do that.
Besides setting a few more breakpoints - which should be pretty cheap - I
don't see much downside to the way it is currently implemented.
Anyway, why did this bother you?
However, I am concerned about the below 'thread until' behaviour. For the
attached test case (kernels.cpp - OpenCL code), following is the debug line
table generated by the compiler.
File name Line number Starting address
kernels.cpp 9 0xacc74d00
kernels.cpp 14 0xacc74d40
kernels.cpp 13 0xacc74dc0
kernels.cpp 14 0xacc74e00
kernels.cpp 25 0xacc74e80
kernels.cpp 25 0xacc74ec0
kernels.cpp 26 0xacc74f00
kernels.cpp 26 0xacc74f40
kernels.cpp 26 0xacc74f80
kernels.cpp 17 0xacc74fc0
kernels.cpp 18 0xacc75000
kernels.cpp 18 0xacc75040
kernels.cpp 19 0xacc75080
kernels.cpp 27 0xacc750c0
kernels.cpp 27 0xacc75140
kernels.cpp 28 0xacc75180
kernels.cpp 28 0xacc751c0
kernels.cpp 29 0xacc75200
kernels.cpp 29 0xacc75240
kernels.cpp 30 0xacc75280
With the ToT lldb, when I am at line 12 (0xacc74d00), if I say 'thread
until 18', the lldb log gives me the following w.r.t breakpoints.
GDBRemoteCommunicationClient::SendGDBStoppointTypePacket() add at addr =
Thread::PushPlan(0x0xa48b38f0): "Stepping from address 0xacc74d00 until we
reach one of:
0xacc75000 (bp: -4)
0xacc75040 (bp: -5)
0xacc75080 (bp: -6)
0xacc750c0 (bp: -7)
0xacc75140 (bp: -8)
0xacc75180 (bp: -9)
0xacc751c0 (bp: -10)
0xacc75200 (bp: -11)
0xacc75240 (bp: -12)
0xacc75280 (bp: -13)
Setting two breakpoints for line number 18 i.e. at 0xacc75000 and
0xacc75040 is understandable from your above reasoning and since we are
anyway setting a breakpoint at the end of the function (line 30 -
0xacc75280), is it necessary to set the breakpoints on line numbers 19, 27,
28, 29 as well i.e. at 0xacc75080 (line 19), 0xacc750c0 (line 27),
0xacc75140 (line 27), 0xacc75180 (line 28), 0xacc751c0 (line 28),
0xacc75200 (line 29), 0xacc75240 (line 29)?
The latter part i.e. setting breakpoints on 19, 27, 28, 29 as well is what
I think is incorrect. Am I missing something here?
kernels.cpp (1.05 KB)