[Dwarf-Discuss] dwarf stack operator for byte swap.
Michael Eager
eager@eagercon.com
Mon Dec 16 17:39:49 GMT 2019
Hi Chirag --
The DWARF Committee is currently on hiatus. We will consider resuming
meetings early next year.
On 12/16/19 4:30 AM, Chirag Patel wrote:
> Hello Michael,
>
> Thanks for opening the issue.
> Can you kindly provide me with the details about what is the next step,
> till issue gets accepted/rejected or any modifications are needed?
>
> Regards,
>
> Chirag Patel
> Software Engineer | Raincode Labs India
> Tel: (+91) 080 41159811
> Mob: (+91) 9049336744
>
>
>
> ------------------------------------------------------------------------
> *From:* Chirag Patel
> *Sent:* 11 November 2019 13:07:19
> *To:* Michael Eager <eager at eagercon.com>; Robinson, Paul
> <paul.robinson at sony.com>; Ron Brender <ron.brender at gmail.com>
> *Cc:* dwarf-discuss at lists.dwarfstd.org <dwarf-discuss at lists.dwarfstd.org>
> *Subject:* RE: [Dwarf-Discuss] dwarf stack operator for byte swap.
> Hello Michael,
>
> Thanks for the confirmation. Kindly inform me if anything needs to be
> updated from myside.
>
> Regards,
>
> Chirag Patel
> Software Engineer | Raincode Labs India
> Tel: (+91) 080 41159811
> Mob: (+91) 9049336744
> www.raincodelabs.com <http://www.raincodelabs.com>
>
>
> -----Original Message-----
> From: Michael Eager <eager at eagercon.com>
> Sent: 08 November 2019 20:04
> To: Chirag Patel <Chirag at raincode.com>; Robinson, Paul
> <paul.robinson at sony.com>; Ron Brender <ron.brender at gmail.com>
> Cc: dwarf-discuss at lists.dwarfstd.org
> Subject: Re: [Dwarf-Discuss] dwarf stack operator for byte swap.
>
> Hi Chirag --
>
> Thanks for your submission.? It was received.
>
> I'm redesigning the DWARF website, in part to address the problem that
> it receives a lot of spam submissions.? Your issue will be posted soon.
>
> On 11/7/19 10:51 PM, Chirag Patel wrote:
>> Hi all,
>>
>> I have sent a comment through http://dwarfstd.org/Comment.php
>>
>> But below is the body of the comment ?
>>
>> Section 2.5.1.7, pg 37
>>
>> DW_OP_byte_swap to Byte Swap the data on top of the dwarf stack.
>>
>> ======================================================================
>> =========
>>
>> Overview
>>
>> ------------
>>
>> For debugging binary with bi-endian marked dwarf DIEs and the some
>> calculation
>>
>> depending at runtime, the data needs to be loaded at runtime and needs
>> to be
>>
>> byte swapped. the depended variable DIE here is marked as big-endian
>> and the
>>
>> host is little-endian. The DW_OP_byte_swap will byte swap the raw data
>> stored
>>
>> in top dwarf stack entry.
>>
>> ?
>>
>> 0x00000057:?? DW_TAG_variable
>>
>>? ??????????????? DW_AT_name????? ("__gbloffset__")
>>
>>? ??????????????? DW_AT_type????? (0x000001e5 "int")
>>
>>? ??????????????? DW_AT_external? (true)
>>
>>? ??????????????? DW_AT_decl_file ("?")
>>
>>? ??????????????? DW_AT_decl_line (8)
>>
>>? ??????????????? DW_AT_location? (DW_OP_addr 0) // pre linkage
>>
>>? ??????????????? DW_AT_linkage_name????? ("_gblsection__")
>>
>>? ??????????????? DW_AT_endianity (DW_END_big)
>>
>> 0x00000170:?? DW_TAG_variable
>>
>>? ??????????????? DW_AT_name????? ("VAR1")
>>
>>? ??????????????? DW_AT_type????? (0x0000010b "fixed.dec.display.72")
>>
>>? ??????????????? DW_AT_decl_file ("?")
>>
>>? ??????????????? DW_AT_decl_line (10)
>>
>>? ??????????????? DW_AT_location? (DW_OP_addr 0x0, DW_OP_call4 0x57,
>> DW_OP_deref_size, 4,
>>
>> DW_OP_dup, DW_OP_constu 0xff, DW_OP_lit0, DW_OP_shl, DW_OP_and,
>> DW_OP_lit24, DW_OP_shl, DW_OP_swap, DW_OP_dup, DW_OP_constu 0xff,
>> DW_OP_lit8, DW_OP_shl, DW_OP_and, DW_OP_lit8, DW_OP_shl, DW_OP_swap,
>> DW_OP_dup, DW_OP_constu 0xff, DW_OP_lit16, DW_OP_shl, DW_OP_and,
>> DW_OP_lit8, DW_OP_shr, DW_OP_swap, DW_OP_constu 0xff, DW_OP_lit24,
>> DW_OP_shl, DW_OP_and, DW_OP_lit24, DW_OP_shr, DW_OP_swap, DW_OP_or,
>> DW_OP_or, DW_OP_or, DW_OP_plus)
>>
>>? ??????????????? DW_AT_linkage_name????? ("VAR1")
>>
>> In above snippet, the DW_OP_byte_swap will replace,
>>
>> DW_OP_dup, DW_OP_constu 0xff, DW_OP_lit0, DW_OP_shl, DW_OP_and,
>> DW_OP_lit24, DW_OP_shl, DW_OP_swap, DW_OP_dup, DW_OP_constu 0xff,
>> DW_OP_lit8, DW_OP_shl, DW_OP_and, DW_OP_lit8, DW_OP_shl, DW_OP_swap,
>> DW_OP_dup, DW_OP_constu 0xff, DW_OP_lit16, DW_OP_shl, DW_OP_and,
>> DW_OP_lit8, DW_OP_shr, DW_OP_swap, DW_OP_constu 0xff, DW_OP_lit24,
>> DW_OP_shl, DW_OP_and, DW_OP_lit24, DW_OP_shr, DW_OP_swap, DW_OP_or,
>> DW_OP_or, DW_OP_or number of operations.
>>
>> Proposed changes to DWARF
>>
>> ---------------------------
>>
>> 2.5.1.7 Special Operation
>>
>> Addition
>>
>> <n> DW_OP_byte_swap
>>
>>? ?????????????? The DW_OP_byte_swap operation pops the top stack
>> entry, byte swaps the value
>>
>>? ?????????????? and pushes back the swapped value on the dwarf stack.
>>
>>? ?????????????? e.g. so 0x12345678 will become 0x78563412, useful to
>> change endianity of raw
>>
>>? ?????????????? data.
>>
>> ---------------------------
>>
>> ?
>>
>> i did not received any confirmation on my mail. How can I check if it
>> was sent correctly?
>>
>> Kindly inform me if anything more needs to be done from myside.
>>
>> Regards,
>>
>> **
>>
>> *Chirag Patel*
>>
>> Software Engineer | Raincode Labs India
>>
>> *Tel*: (+91) 080 41159811
>>
>> *Mob*: (+91) 9049336744
>>
>> _www.raincodelabs.com <http://www.raincodelabs.com/>_
>>
>> linkedin-button <https://in.linkedin.com/in/chirag-patel->
>>
>> *From:*Chirag Patel <Chirag at raincode.com>
>> *Sent:* 29 October 2019 17:10
>> *To:* Michael Eager <eager at eagercon.com>; Robinson, Paul
>> <paul.robinson at sony.com>; Ron Brender <ron.brender at gmail.com>
>> *Cc:* dwarf-discuss at lists.dwarfstd.org
>> *Subject:* Re: [Dwarf-Discuss] dwarf stack operator for byte swap.
>>
>> Hello,
>>
>> Thank you all for prompt reply.
>>
>> @Robinson, Paul <mailto:paul.robinson at sony.com>,
>>
>> Thanks for the shorter list of operators, but as Michael has
>> suggested, i have added a vendor specific operator for that in
>> llvm/lldb(fork of our branch anyways).
>>
>> the operator, pops the stack entry and byte reverses the value and
>> pushes it back on the stack.
>>
>> @Ron Brender <mailto:ron.brender at gmail.com>
>>
>> The operator that i was suggesting, pops the top of the stack,
>> reverses the bytes and pushes it on the stack(like neg operator does
>> for negation).(on second thought the byte_rev would be a better name)
>>
>> About the other cases you suggested, i sure hope others can help to
>> zero in for perfect
>>
>> design to cover wide range.
>>
>> @Michael Eager <mailto:eager at eagercon.com>
>>
>> Thanks, i have tried the same for our fork of llvm/lldb branch and it
>> seems to be working well(for our case :).
>> https://gitlab.phidani.be/Chirag.Patel
>>
>> Thank you all for the helpful comments. i will open a dwarf
>> enhancement request soon.
>>
>> Best Regards.
>>
>> *Chirag Patel*
>>
>> Software Engineer*| *Raincode Labs India
>>
>> Tel: (+91) 080 41159811
>>
>> Mob: (+91) 9049336744
>>
>> <https://www.linkedin.com/in/chirag-patel-/>
>>
>> _
>>
>> <https://www.linkedin.com/in/chirag-patel-/>_
>>
>> <https://www.linkedin.com/in/chirag-patel-/>
>>
>> ----------------------------------------------------------------------
>> --
>>
>> *From:*Michael Eager <eager at eagercon.com <mailto:eager at eagercon.com>>
>> *Sent:* 28 October 2019 20:37
>> *To:* Robinson, Paul <paul.robinson at sony.com
>> <mailto:paul.robinson at sony.com>>; Chirag Patel <Chirag at raincode.com
>> <mailto:Chirag at raincode.com>>
>> *Cc:* dwarf-discuss at lists.dwarfstd.org
>> <mailto:dwarf-discuss at lists.dwarfstd.org>
>> <dwarf-discuss at lists.dwarfstd.org
>> <mailto:dwarf-discuss at lists.dwarfstd.org>>
>> *Subject:* Re: [Dwarf-Discuss] dwarf stack operator for byte swap.
>>
>> Hi Chirag --
>>
>> A byte-swap operator would be a reasonable addition to the DWARF
>> interpreter.
>>
>> In addition to writing a proposal as Paul suggests, one option I would
>> recommend you consider is to create a user-defined operation to
>> perform this byte-swap operation and give it a value in the range
>> between DW_OP_lo_user and DW_OP_hi_user.? Of course, this user-defined
>> would need to be implemented not only in the producer (i.e., compiler)
>> but in any consumers (i.e., debugger).
>>
>> When a new version of the DWARF Standard is released, this operation
>> would be assigned a new value.
>>
>> On 10/28/19 6:53 AM, Robinson, Paul via Dwarf-Discuss wrote:
>>? > Hello Chirag,
>>? >
>>? > Regarding a byte-swap operation, it seems that you have a
>> reasonable? > use-case on a bi-endian machine.? Feel free to request a
>> new operator on? > the ?public comments? page at
>> http://dwarfstd.org/Comment.php? >? > Note that a byte-swap operator
>> would swap all bytes in the top-of-stack? > value, which on your
>> 64-bit machine would of course be a 64-bit value.
>>? > As you want a 32-bit swapped value, you would still need to do a
>> shift? > afterward, but even so, ?DW_OP_byte_swap DW_OP_const1u 32 DW_OP_shr?
>>? > would be considerably shorter than what you have to do now.
>>? >
>>? > Of course a new operator would be introduced in a new DWARF
>> revision,? > which is likely to be years away.? In the meantime let me
>> suggest a? > shorter expression for doing the byte-swap operation.
>> The book? > ?Hacker?s Delight? shows a straightforward 32-bit byte
>> swap with masks? > no wider than 16 bits, as follows:
>>? >
>>? >? ?????????????? x = (x << 24) | ((x & 0xff00) << 8) | ((x >> 8) &
>> > 0xff00) | (x >> 24);? >? > Your 64-bit machine will of course use
>> 64-bit values on the expression? > stack, so to keep the result
>> ?32-bit clean? we want to do one additional? > mask:
>>? >
>>? >? ?????????????? x = ((x & 0xff) << 24) | ((x & 0xff00) << 8) | ((x
>> >> 8)? > & 0xff00) | (x >> 24);? >? > Translating this into a DWARF
>> expression, I get the following:
>>? >
>>? >? ?????????????? DW_OP_dup, DW_OP_const1u 0xff, DW_OP_and,
>> DW_OP_lit24,? > DW_OP_shl, DW_OP_swap, DW_OP_dup, DW_OP_const2u
>> 0xff00, DW_OP_and,? > DW_OP_lit8, DW_OP_shl, DW_OP_swap, DW_OP_dup,
>> DW_OP_lit8, DW_OP_shr,? > DW_OP_const2u 0xff00, DW_OP_and, DW_OP_swap,
>> DW_OP_lit24, DW_OP_shr,? > DW_OP_or, DW_OP_or, DW_OP_or? >? > I hope
>> this is helpful to you.
>>? >
>>? > --paulr
>>? >
>>? > *From:* Dwarf-Discuss <dwarf-discuss-bounces at lists.dwarfstd.org
>> <mailto:dwarf-discuss-bounces at lists.dwarfstd.org>> *On? > Behalf Of
>> *Chirag Patel via Dwarf-Discuss? > *Sent:* Monday, October 28, 2019
>> 12:47 AM? > *To:* dwarf-discuss at lists.dwarfstd.org
>> <mailto:dwarf-discuss at lists.dwarfstd.org>
>>? > *Subject:* [Dwarf-Discuss] dwarf stack operator for byte swap.
>>? >
>>? > Hello Dwarf experts.
>>? >
>>? > I am currently working trying to encode dwarf of binaries with
>> having? > bi-endian variables marked with DW_AT_endianity attribute.
>>? >
>>? > The location calculation for some? variable depends on other
>> variable? > with different endianity, also the value of this other
>> variable is known? > at runtime.
>>? >
>>? > At the moment I am using location list to calculate the correct
>> location? > of first variable and list of dwarf operators to reverse
>> the endianity? > of variable ?__gbloffset__? in below case (I only
>> needed lower 32 bits? > on 64 bit machine).
>>? >
>>? > 0x000001e5: DW_TAG_base_type
>>? >
>>? >? ?DW_AT_byte_size ?(0x04)
>>? >
>>? >? ? DW_AT_encoding? (DW_ATE_signed)
>>? >
>>? >? ??????????????? DW_AT_name????? ("int")? >? >
>> DW_AT_endianity (DW_END_big)? >? > ?? >? > 0x00000057:
>> DW_TAG_variable? >? >? ??????????????? DW_AT_name
>> ("__gbloffset__")? >? >? ??????????????? DW_AT_type????? (0x000001e5
>> "int")? >? >? ??????????????? DW_AT_external? (true)? >? >
>> DW_AT_decl_file ("?")? >? >? ??????????????? DW_AT_decl_line (8)? >? >
>> DW_AT_location? (DW_OP_addr 0) // pre linkage? >? >
>> DW_AT_linkage_name????? ("_gblsection__")? >? > 0x00000170:
>> DW_TAG_variable? >? >? ??????????????? DW_AT_name????? ("VAR1")? >? >
>> DW_AT_type????? (0x0000010b "fixed.dec.display.72")? >? >
>> DW_AT_decl_file ("?")? >? >? ??????????????? DW_AT_decl_line (10)? >
>> >? ??????????????? DW_AT_location? (DW_OP_addr 0x0, DW_OP_call4 0x57,
>> > DW_OP_deref_size, 4,? >? > DW_OP_dup, DW_OP_constu 0xff, DW_OP_lit0,
>> DW_OP_shl, DW_OP_and,? > DW_OP_lit24, DW_OP_shl, DW_OP_swap,
>> DW_OP_dup, DW_OP_constu 0xff,? > DW_OP_lit8, DW_OP_shl, DW_OP_and,
>> DW_OP_lit8, DW_OP_shl, DW_OP_swap,? > DW_OP_dup, DW_OP_constu 0xff,
>> DW_OP_lit16, DW_OP_shl, DW_OP_and,? > DW_OP_lit8, DW_OP_shr,
>> DW_OP_swap, DW_OP_constu 0xff, DW_OP_lit24,? > DW_OP_shl, DW_OP_and,
>> DW_OP_lit24, DW_OP_shr, DW_OP_swap, DW_OP_or,? > DW_OP_or, DW_OP_or,
>> DW_OP_plus)? >? >? ??????????????? DW_AT_linkage_name????? ("VAR1")? >
>> > In above snippet of dwarf dump, I am using yellow highlighted list
>> of? > operators to swap the bytes.
>>? >
>>? > I think there should be a support for DW_OP_byte_swap simple
>> operator to? > accomplice this simple task. Does this idea looks like it can be useful?
>>? > Is there any specific reason why dwarf spec does not have it or I
>> am? > missing something subtle.
>>? >
>>? > I hope I conveyed the idea properly, apologies in advanced as
>> English is? > not my first language.
>>? >
>>? > **
>>? >
>>? > *Thanks and regards,*
>>? >
>>? > **
>>? >
>>? > *Chirag Patel*
>>? >
>>? > Software Engineer | Raincode Labs India? >? > *Tel*: (+91) 080
>> 41159811? >? > *Mob*: (+91) 9049336744? >? > www.raincodelabs.com <http://www.raincodelabs.com>
>> <http://www.raincodelabs.com> <http://www.raincodelabs.com/>__? >? >
>> linkedin-button <https://in.linkedin.com/in/chirag-patel->
>>? >
>>? >
>>? > _______________________________________________
>>? > Dwarf-Discuss mailing list
>>? > Dwarf-Discuss at lists.dwarfstd.org
>> <mailto:Dwarf-Discuss at lists.dwarfstd.org>
>>? > http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
>>? >
>>
>> --
>> Michael Eager eager at eagercon.com <mailto:eager at eagercon.com>
>> 1960 Park Blvd., Palo Alto, CA 94306
>>
>
> --
> Michael Eager??? eager at eagercon.com
> 1960 Park Blvd., Palo Alto, CA 94306
--
Michael Eager eager at eagercon.com
1960 Park Blvd., Palo Alto, CA 94306
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