[lldb-dev] llvm changing line table info from DWARF 2 to DWARF 4

Thu Oct 20 11:50:37 PDT 2016

I think a hardcoded value of 1 for maximum_operations_per_instruction will work like it does today – 1 linetable entry per Hexagon packet, which may have 1-4 instructions in it. Hexagon executes 1 packet at a time, so anywhere from 1-4 instructions at once.

At O0, the compiler doesn’t packetize instructions, so 1 instruction is run at a time. At 01 it will, but it doesn’t do many other optimizations. We should still have 1 line per packet. O2 and O3 can move instructions around, so will have up to 4 source lines in 1 packet. I think we’ll need to experiment internally with what that means for the debugger, once we get this change.

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From: Eric Christopher [mailto:echristo at gmail.com] 
Sent: Wednesday, October 19, 2016 6:09 PM
To: Tim Hammerquist <penryu at gmail.com>
Cc: Greg Clayton <gclayton at apple.com>; Ted Woodward <ted.woodward at codeaurora.org>; LLDB <lldb-dev at lists.llvm.org>
Subject: Re: [lldb-dev] llvm changing line table info from DWARF 2 to DWARF 4

On Wed, Oct 19, 2016 at 3:34 PM Tim Hammerquist <penryu at gmail.com <mailto:penryu at gmail.com> > wrote:

I was mistaken.

The system toolchain builds stage1 llvm, clang & co.

The system toolchain builds lldb containing the llvm/clang/etc bits.

The system toolchain builds gtest test programs. 

The stage1 compiler builds the python test inferiors.

OK, then it sounds like at least some of the test programs are built with the new compiler? IIRC the python test inferiors here are the programs that are the meat of the testsuite for lldb yes?

If so, then on check-in we should possibly see some difference on some bot if they all use the same general configuration.  I don't have a current checkout so I don't know if the default -g is used or if it's set to a different dwarf level. Currently it looks like clang will use dwarf4 by default with -g:

echristo at dzur ~/tmp> ~/builds/build-llvm/bin/clang -c foo.c -o - -target x86_64-apple-macosx10.11 -g | llvm-dwarfdump - | grep version | grep -v clang

0x00000000: Compile Unit: length = 0x00000037 version = 0x0004 abbr_offset = 0x0000 addr_size = 0x08 (next unit at 0x0000003b)

         version: 2

where the first line is the debug_info header and the second is the version in the line table.

Ted/Greg: Relatedly, what brought this up was the vliw aspect with maximum_operations_per_instruction - it's being hard coded to 1 here and I'm not sure how we want to deal with that on hexagon? Currently it'll be hard set to 1 so line stepping will work as I imagine it currently does. That said, if we wanted to take advantage of it then that's different. Primarily I wasn't sure if Ted and folk had a debugger that did take advantage of it if it was there.

Thanks!

-eric

On Wed, Oct 19, 2016 at 3:28 PM, Eric Christopher <echristo at gmail.com <mailto:echristo at gmail.com> > wrote:

On Wed, Oct 19, 2016 at 3:26 PM Tim Hammerquist <penryu at gmail.com <mailto:penryu at gmail.com> > wrote:

The LLDB job in  <http://llvm.org/> llvm.org will build a stage1 RA with llvm+clang+libcxx+compiler-rt using the system compiler, and use the new compiler to build lldb.

By default, this is kicked off automatically when a clang stage1 RA is successful, but can be manually triggered to build HEAD, or any revision desired.

The python test suite (invoked with the xcodebuild target lldb-python-test-suite) uses the newly built compiler to build its test programs.

http://lab.llvm.org:8080/green/job/lldb_build_test/21202/consoleFull#console-section-4

However, the gtest suite (target lldb-gtest) uses the system (Xcode toolchain) compiler to build test programs.

http://lab.llvm.org:8080/green/job/lldb_build_test/21202/artifact/lldb/test_output.zip

This seems like something that should be fixed :)

-eric

-Tim

On Wed, Oct 19, 2016 at 2:36 PM, Eric Christopher <echristo at gmail.com <mailto:echristo at gmail.com> > wrote:

>From chatting with Tim it sounds like at least one lldb bot uses the ToT compiler - we should probably verify that not only does it use that to build lldb but uses it for the tests. That'll get us at least some testing here.

-eric

On Wed, Oct 19, 2016 at 12:55 PM Greg Clayton via lldb-dev <lldb-dev at lists.llvm.org <mailto:lldb-dev at lists.llvm.org> > wrote:

I believe we are good, but it would be good to verify via testing once a compiler becomes available.

Greg

> On Oct 19, 2016, at 12:19 PM, Ted Woodward via lldb-dev <lldb-dev at lists.llvm.org <mailto:lldb-dev at lists.llvm.org> > wrote:
>
> This might affect us. Do we handle it correctly?
>
> https://reviews.llvm.org/D16697
>
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Tim <penryu at gmail.com <mailto:penryu at gmail.com> >

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