[llvm-dev] Source locations missing when using xray-account

[Matthew Pickering via llvm-dev]

Is anyone able to help me with this or suggest where I might be able
to get help?

Matt
On Mon, Nov 26, 2018 at 3:02 PM Matthew Pickering
<matthewtpickering at gmail.com> wrote:
>
> Hi all,
>
> I am trying to add XRay support to the IR produced by GHC. Getting the
> basics working is not too complicated after adding the right function
> attribute but any analysis shows the function names but not the
> locations of the functions.
>
> In particular, I run a program which has been instrumented as follows:
>
> XRAY_OPTIONS="patch_premain=true xray_mode=xray-basic verbosity=1" ./llvm
>
> which then writes out an xray-log file.
>
> ==4193==XRay: Log file in 'xray-log.llvm.hgD9oi'
> ==4193==Cleaned up log for TID: 4193
>
> I then attempt to use the xray-account utility to analyse the log but
> whilst the functions are named, the locations of the functions are
> displayed as <invalid>:0:0:.
>
> > llvm-xray account  -sort=sum -sortorder=dsc -instr_map ./llvm  xray-log.llvm.hgD9oi
>
> Functions with latencies: 5
>    funcid      count [      min,       med,       90p,       99p,
>  max]       sum  function
>         6          9 [ 0.000006,  0.000006,  0.000040,  0.000040,
> 0.000040]  0.000089  <invalid>:0:0: fqux
> ... 4 lines omitted
>
> If I then inspect the executable with llvm-dwarfdump, I can see that
> the debug information for fqux clearly lists the location as well.
>
> 0x00000918:   DW_TAG_subprogram
>                 DW_AT_low_pc  (0x00000000004207c8)
>                 DW_AT_high_pc (0x0000000000420817)
>                 DW_AT_frame_base  (DW_OP_reg7 RSP)
>                 DW_AT_linkage_name  ("fqux")
>                 DW_AT_name  ("fqux")
>                 DW_AT_decl_file ("TODO/llvm.hs")
>                 DW_AT_decl_line (8)
>                 DW_AT_external  (true)
>
> I suspect this is a problem with the DWARF information as when I try
> to use `llvm-symboliser` with address 0x00000000004207c8 as retrieved
> from the above paste, the source location is also not reported.
>
> So, can anyone give me some practical advice about how to troubleshoot
> this problem/validate the DWARF information that is produced?
>
> It might also be helpful is someone could point me to some
> documentation which explains at a high-level how llvm-symboliser
> works. Reading the source code was too difficult for me as I am not
> very experienced with C++ programming.
>
> Many thanks for your help,
>
> Matt