Hello, Thank you all for prompt reply.
@Robinson, Paul<mailto:paul.robin...@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.bren...@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:ea...@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 <http://www.raincodelabs.com/> <https://www.linkedin.com/in/chirag-patel-/> [cid:68b118f1-419e-4f8e-a7ba-1d94b0379f85] ________________________________ From: Michael Eager <ea...@eagercon.com> Sent: 28 October 2019 20:37 To: Robinson, Paul <paul.robin...@sony.com>; Chirag Patel <chi...@raincode.com> Cc: dwarf-discuss@lists.dwarfstd.org <dwarf-discuss@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-boun...@lists.dwarfstd.org> *On > Behalf Of *Chirag Patel via Dwarf-Discuss > *Sent:* Monday, October 28, 2019 12:47 AM > *To:* dwarf-discuss@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/>__ > > linkedin-button <https://in.linkedin.com/in/chirag-patel-> > > > _______________________________________________ > Dwarf-Discuss mailing list > Dwarf-Discuss@lists.dwarfstd.org > http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org > -- Michael Eager ea...@eagercon.com 1960 Park Blvd., Palo Alto, CA 94306
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