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Linux Getting Extensive x86 Assembly Code Refresh

Posted by Soulskill on from the code-run-through-de-spaghettifier dept.

jones_supa writes: A massive x86 assembly code spring cleaning has been done in a pull request that is to end up in Linux 4.1. The developers have tried testing the code on many different x86 boxes, but there's risk of regression when exposing the code to many more systems in the days and weeks ahead. That being said, the list of improvements is excellent. There are over 100 separate cleanups, restructuring changes, speedups and fixes in the x86 system call, IRQ, trap and other entry code, part of a heroic effort to deobfuscate a decade old spaghetti assembly code and its C code dependencies.

4 of 209 comments (clear)

  1. Re:Speedups? by Guy+Harris · · Score: 3, Informative

    > There are over 100 separate ... speedups

    The last time I looked, which was quite a few years ago TBH, the BSDs have, IIRC, less than 100 lines of x86 assembly, in the bootstrap.

    From relatively-recent FreeBSD:

    $ find sys/i386 -name '*.[sS]' -print | xargs wc -l
    208 sys/i386/acpica/acpi_wakecode.S
    40 sys/i386/bios/smapi_bios.S
    396 sys/i386/i386/apic_vector.s
    78 sys/i386/i386/atpic_vector.s
    160 sys/i386/i386/bioscall.s
    470 sys/i386/i386/exception.s
    900 sys/i386/i386/locore.s
    279 sys/i386/i386/mpboot.s
    831 sys/i386/i386/support.s
    538 sys/i386/i386/swtch.s
    179 sys/i386/i386/vm86bios.s
    37 sys/i386/linux/linux_locore.s
    127 sys/i386/linux/linux_support.s
    32 sys/i386/svr4/svr4_locore.s
    202 sys/i386/xbox/pic16l.s
    494 sys/i386/xen/exception.s
    361 sys/i386/xen/locore.s
    5332 total
    $ find sys/amd64 -name '*.[sS]' -print | xargs wc -l
    282 sys/amd64/acpica/acpi_wakecode.S
    326 sys/amd64/amd64/apic_vector.S
    73 sys/amd64/amd64/atpic_vector.S
    541 sys/amd64/amd64/cpu_switch.S
    906 sys/amd64/amd64/exception.S
    88 sys/amd64/amd64/locore.S
    236 sys/amd64/amd64/mpboot.S
    56 sys/amd64/amd64/sigtramp.S
    732 sys/amd64/amd64/support.S
    75 sys/amd64/ia32/ia32_exception.S
    161 sys/amd64/ia32/ia32_sigtramp.S
    38 sys/amd64/linux32/linux32_locore.s
    124 sys/amd64/linux32/linux32_support.s
    246 sys/amd64/vmm/intel/vmx_support.S
    42 sys/amd64/vmm/vmm_support.S
    3926 total

    It's about 45,000 lines in Linux 3.19's arch/x86. A fair bit of that is crypto code, presumably either generally hand-optimized or using various new instructions to do various crypto calculations.

  2. Re:opportunity for backdoors? by phantomfive · · Score: 1, Informative

    Who can sight read assembly anymore?

    Anyone who reasonably calls themselves a programmer.

    --
    "First they came for the slanderers and i said nothing."
  3. Re:Cruft by benjymouse · · Score: 4, Informative

    For some time now, Mark Russinovich at Microsoft has been talking about just how bad the Windows kernel was/is in his blog.

    I think you are confused. It was not Mark Russinovich, but rather Linus Torvalds, and he was talking about the Linux kernel, not the Windows kernel.

    "I mean, sometimes it's a bit sad that we are definitely not the streamlined, small, hyper-efficient kernel that I envisioned 15 years ago...The kernel is huge and bloated, and our icache footprint is scary. I mean, there is no question about that. And whenever we add a new feature, it only gets worse."

    Glad I could help.

    --
    Reading slashdot one-liner: (irm http://rss.slashdot.org/Slashdot/slashdot).rdf.item | fl title,desc*
  4. Re:It's only a modest refresh by Steve+Hamlin · · Score: 3, Informative

    +5 Informative / Insightful for parent

    For background, the parent comment is Matthew Dillon, compiler and kernel hacker on Amiga/BSD/Linux and founder of DragonFly BSD (fork of FreeBSD).

    http://en.wikipedia.org/wiki/D...