[Dwarf-Discuss] DWARF and online-compiled programs (Simon Brand)

Simon Brand simon at codeplay.com
Mon Jun 13 01:07:33 PDT 2016

Thanks for your thoughts.

Could you expand on why this is not in the spirit of DW_AT_location?

Those two alternatives seem reasonable, but we'd really like to have a 
method standardised in DWARF for this so that the compiler and debugger 
don't need an additional contract between them.

Also, the source might not be "in memory", as it might be placed in a 
binary segment which is not loaded. The debugger should be interpreting 
the location as something like the ELF virtual address to locate the 
source in the object file.

On 10/06/16 16:13, Ron Brender wrote:
> The original proposal extends DW_AT_location in a way that seems not 
> really in the spirit and intent of that attribute.
> Two alternatives come to mind:
> 1) Invent a new pseudo-device to use in the name string of a standard 
> DW_AT_name attribute. For the name "inmemory:\\0x55555555", the 
> debugger would recognize the prefix and decode it's follow-on directly 
> (sort of like the "file:\\..." URL syntax supported in some browsers). 
> This puts the burden of agreement on the JIT and its debugger and 
> requires nothing new of DWARF as such.
> 2) Add a new implementation-defined attribute DW_AT_in_memory_source 
> whose class address value is the address in memory of the source 
> string. Use this attribute as an alternative to DW_AT_name. Since 
> there is no named file that contains the source, an omitted DW_AT_name 
> (or one with a null string) is sensible, This also requires nothing 
> new of DWARF.
> Something to consider...
> Ron
> On Thu, Jun 9, 2016 at 2:02 PM, Robinson, Paul <paul.robinson at sony.com 
> <mailto:paul.robinson at sony.com>> wrote:
>     In principle you could have generated source JIT-compiled on a
>     device that has no filesystem in the usual sense, or maybe has one
>     but it isn't writable.
>     Seems like a reasonable approach.
>     --paulr
>     *From:*Dwarf-Discuss
>     [mailto:dwarf-discuss-bounces at lists.dwarfstd.org
>     <mailto:dwarf-discuss-bounces at lists.dwarfstd.org>] *On Behalf Of
>     *Bishop, John E
>     *Sent:* Thursday, June 09, 2016 10:10 AM
>     *To:* dwarf-discuss at lists.dwarfstd.org
>     <mailto:dwarf-discuss at lists.dwarfstd.org>
>     *Subject:* Re: [Dwarf-Discuss] DWARF and online-compiled programs
>     (Simon Brand)
>     --[ quote ]--
>     I'm writing this email in particular to address the problem of
>     referencing source files in DWARF for online-compiled programs.
>     The issue is that programming models such as OpenCL can often have
>     source generated at runtime,which is compiled online, with its
>     output not written to file. This raises an issue for the compiler:
>     in the generated DWARF, what should it put as the file name of the
>     compile unit and associated line table information?
>     --[ end quote ]—
>     I’m inclined to say that in the general case the compiler should
>     create an actual file and use it, but I like the in-the-binary
>     solution for short pseudo-sources.
>     This would go into V6, right?
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Simon Brand
Staff Software Engineer
Codeplay Software Ltd
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