Re: DWZ 0.14 released

[Allan Sandfeld Jensen <linux@carewolf.com>]

Btw, question for gcc/binutils

Any reason the work done by tools like dwz couldn't be done in the compiler or 
linker? Seems a bit odd to have a post-linker that optimizes the generated 
code, when optimizations should already be enabled.

Best regards
Allan

On Montag, 8. März 2021 13:43:11 CET Tom de Vries wrote:
> Hi,
> 
> DWZ 0.14 has been released.
> 
> You can download dwz from the sourceware FTP server here:
> 
>         https://sourceware.org/ftp/dwz/releases/
>         ftp://sourceware.org/pub/dwz/releases/
> 
> The vital stats:
> 
>   Size    md5sum                            Name
>   184KiB  cf60e4a65d9cc38c7cdb366e9a29ca8e  dwz-0.14.tar.gz
>   144KiB  1f1225898bd40d63041d54454fcda5b6  dwz-0.14.tar.xz
> 
> There is a web page for DWZ at:
> 
>         https://sourceware.org/dwz/
> 
> DWZ 0.14 includes the following changes and enhancements:
> 
> * DWARF 5 support. The tool now handles most of DWARF version 5
>   (at least everything emitted by GCC when using -gdwarf-5).
> 
>   Not yet supported are DW_UT_type units (DWARF 4 .debug_types
>   are supported), .debug_names (.gdb_index is supported) and some
>   forms and sections that are only emitted by GCC when
>   generating Split DWARF (DW_FORM_strx and .debug_str_offsets,
>   DW_FORM_addrx and .debug_addr, DW_FORM_rnglistx and
>   DW_FORM_loclistsx). https://sourceware.org/PR24726
> 
> * .debug_sup support. DWARF Supplementary Object Files
>   (DWARF 5, section 7.3.6) can now be generated when using
>   the --dwarf-5 option. To keep compatibility with existing DWARF
>   consumers this isn't the default yet.
> 
>   Without the --dwarf-5 option instead of a .debug_sup section dwz
>   will generate a .gnu_debugaltlink section and will use
>   DW_FORM_GNU_strp_alt and DW_FORM_GNU_reg_alt, instead of
>   DW_FORM_strp_sup and DW_FORM_ref_sup
> 
> * An experimental optimization has been added that exploits the
>   One-Definition-Rule of C++.  It's enabled using the --odr option, and
>   off by default.  This optimization causes struct/union/class DIEs with
>   the same name to be considered equal.  The optimization can be set to
>   a lower aggressiveness level using --odr-mode=basic, to possibly be
>   able to workaround problems without having to switch off the
>   optimization altogether.
> 
> * The clean-up of temporary files in hardlink mode has been fixed.
> 
> * The DIE limits --low-mem-die-limit <n> / -l <n> and
>   --max-die-limit <n> / -L <n> can now be disabled using respectively
>   -l none and -L none.  Note that -l none disables the limit, whereas
>   -l 0 sets the limit to zero.
> 
> * The usage message has been:
>   - updated to show that -r and -M are exclusive.
>   - updated to show at -v and -? cannot be combined with other options.
>   - extended to list all options in detail.
>   - restyled to wrap at 80 chars.
> 
> * An option --no-import-optimize was added that switches off an
>   optimization that attempts to reduce the number of
>   DW_TAG_imported_unit DIEs.  This can be used f.i. in case the
>   optimization takes too long.
> 
> * A heuristic has been added that claims more memory earlier (without
>   increasing the peak memory usage) to improve compression time.
> 
> * A heuristic has been added that estimates whether one of the two DIE
>   limits will be hit.  If so, it will do an exact DIE count to verify
>   this.  If the exact DIE count finds that the low-mem DIE limit is
>   indeed hit, processing is done in low-mem mode from the start, rather
>   than processing in regular mode first.  If the exact DIE count finds
>   that the max DIE limit is indeed hit, processing is skipped
>   altogether.
> 
> * Various other performance improvements.
> 
> * A case where previously we would either hit the assertion
>   "dwz: dwz.c:9461: write_die: Assertion `refd != NULL' failed" (in
>   regular mode) or a segmentation fault (in low-mem mode), now is
>   handled by "dwz: Couldn't find DIE at DW_FORM_ref_addr offset 0x<n>".
> 
> * A case where a reference from a partial unit to a compile unit was
>   generated has been fixed.  This could happen if a DIE was referenced
>   using a CU-relative DWARF operator.
> 
> * A case has been fixed for low-mem mode where instead of issuing
>   "dwz: Couldn't find DIE referenced by  DW_OP_GNU_implicit_pointer" dwz
>   would run into a segfault instead.
> 
> * A multi-file case where we run into ".debug_line reference above end
>   of section" has been fixed.
> 
> * The following assertion failures were fixed:
>   - dwz: dwz.c:9310: write_die: Assertion `
>       value && refdcu->cu_kind != CU_ALT
>     ' failed.
>   - dwz: dwz.c:9920: recompute_abbrevs: Assertion `
>       off == cu_size
>     ' failed.
> 
> * The assert condition of this assertion has been fixed:
>   - write_types: Assertion `ref && ref->die_dup == NULL'.