[Bug corefiles/31494] gcore should generate sparse cores

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https://sourceware.org/bugzilla/show_bug.cgi?id=31494

--- Comment #3 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pedro Alves <palves@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=431a6b091d3106bc9750d82f50535d35d760f920

commit 431a6b091d3106bc9750d82f50535d35d760f920
Author: Pedro Alves <pedro@palves.net>
Date:   Fri Mar 22 12:31:29 2024 +0000

    Teach GDB to generate sparse core files (PR corefiles/31494)

    This commit teaches GDB's gcore command to generate sparse core files
    (if supported by the filesystem).

    To create a sparse file, all you have to do is skip writing zeros to
    the file, instead lseek'ing-ahead over them.

    The sparse logic is applied when writing the memory sections, as
    that's where the bulk of the data and the zeros are.

    The commit also tweaks gdb.base/bigcore.exp to make it exercise
    gdb-generated cores in addition to kernel-generated cores.  We
    couldn't do that before, because GDB's gcore on that test's program
    would generate a multi-GB non-sparse core (16GB on my system).

    After this commit, gdb.base/bigcore.exp generates, when testing with
    GDB's gcore, a much smaller core file, roughly in line with what the
    kernel produces:

     real sizes:

     $ du --hu testsuite/outputs/gdb.base/bigcore/bigcore.corefile.*
     2.2M    testsuite/outputs/gdb.base/bigcore/bigcore.corefile.gdb
     2.0M    testsuite/outputs/gdb.base/bigcore/bigcore.corefile.kernel

     apparent sizes:

     $ du --hu --apparent-size
testsuite/outputs/gdb.base/bigcore/bigcore.corefile.*
     16G     testsuite/outputs/gdb.base/bigcore/bigcore.corefile.gdb
     16G     testsuite/outputs/gdb.base/bigcore/bigcore.corefile.kernel

    Time to generate the core also goes down significantly.  On my machine, I
get:

      when writing to an SSD, from 21.0s, down to 8.0s
      when writing to an HDD, from 31.0s, down to 8.5s

    The changes to gdb.base/bigcore.exp are smaller than they look at
    first sight.  It's basically mostly refactoring -- moving most of the
    code to a new procedure which takes as argument who should dump the
    core, and then calling the procedure twice.  I purposely did not
    modernize any of the refactored code in this patch.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31494
    Reviewed-By: Lancelot Six <lancelot.six@amd.com>
    Reviewed-By: Eli Zaretskii <eliz@gnu.org>
    Reviewed-By: John Baldwin <jhb@FreeBSD.org>
    Change-Id: I2554a6a4a72d8c199ce31f176e0ead0c0c76cff1

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