Messages in this thread | | | From | Arnd Bergmann <> | Date | Thu, 23 Jul 2020 13:42:16 +0200 | Subject | Re: [PATCH v3 11/11] x86: support i386 with Clang |
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On Thu, Jul 23, 2020 at 1:07 PM Sedat Dilek <sedat.dilek@gmail.com> wrote: > On Thu, Jul 23, 2020 at 11:17 AM Thomas Gleixner <tglx@linutronix.de> wrote: > > Thomas Gleixner <tglx@linutronix.de> writes: > > I have applied this patch-series v3 but some basics of "i386" usage > are not clear to me when I wanted to test it and give some feedback. > > [1] is the original place in CBL where this was reported and I have > commented on this. > > Beyond some old cruft in i386_defconfig like non-existent > "CONFIG_CRYPTO_AES_586" I have some fundamental questions: > > What means "ARCH=i386" and where it is used (for)? > > I can do: > > $ ARCH=x86 make V=1 -j3 $MAKE_OPTS i386_defconfig > $ make V=1 -j3 $MAKE_OPTS i386_defconfig > > ...which results in the same .config. > > Whereas when I do: > > $ ARCH=i386 make V=1 -j3 $MAKE_OPTS i386_defconfig > > ...drops CONFIG_64BIT line entirely. > > But "# CONFIG_64BIT is not set" is explicitly set in > arch/x86/configs/i386_defconfig but gets dropped. > > Unsure if above is the same like: > $ ARCH=i386 make V=1 -j3 $MAKE_OPTS defconfig
The logic was introduced when arch/i386 and arch/x86_64 got merged into arch/x86, to stay compatible with the original behavior that would produce a 32-bit or 64-bit kernel depending on which machine you are running on.
There are probably not a lot of people building kernels on 32-bit machines any more (real 32-bit machines are really slow compared to modern ones, and 64-bit machines running 32-bit distros usually want a 64-bit kernel), so it could in theory be changed.
It will certainly break someone's workflow though, so nobody has proposed actually changing it so far.
> When generating via "make ... i386_defconfig" modern gcc-9 and and a > snapshot version of clang-11 build both with: > > $ ARCH=x86 make V=1 -j3 $MAKE_OPTS > ... -march=i686 -mtune=generic ... > > Checking generated .config reveals: > > CONFIG_M686=y > > So, I guess modern compilers do at least support "i686" as lowest CPU?
i686 compiler support goes back to the 1990s, and the kernel now requires at least gcc-4.9 from 2014, so yes.
> Nick D. says: > > I usually test with make ... i386_defconfig. > > Can you enlighten a bit? > > Of course, I can send a patch to remove the "CONFIG_CRYPTO_AES_586=y" > line from i386_defconfig.
The "i386" in i386_defconfig is just a synonym for x86-32, it does not imply a particular CPU generation. The original i386 is no longer supported, i486sx (barely) is and in practice most 32-bit Linux code gets compiled for some variant of i586 or i686 variant but run on 64-bit hardware.
Arnd
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