Messages in this thread | | | Date | Mon, 6 Mar 2023 10:35:17 +0100 | Subject | Re: [PATCH v3 00/24] Remove COMMAND_LINE_SIZE from uapi | From | Alexandre Ghiti <> |
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On 3/3/23 17:40, Arnd Bergmann wrote: > On Fri, Mar 3, 2023, at 12:59, Alexandre Ghiti wrote: >> On 3/2/23 20:50, H. Peter Anvin wrote: >>> On March 1, 2023 7:17:18 PM PST, Palmer Dabbelt <palmer@dabbelt.com> wrote: >>>>>> Commit 622021cd6c560ce7 ("s390: make command line configurable"), >>>>>> I assume? >>>>> Yes, sorry for that. I got distracted while writing and used the wrong >>>>> branch to look this up. >>>> Alex: Probably worth adding that to the list in the cover letter as it looks like you were planning on a v4 anyway (which I guess you now have to do, given that I just added the issue to RISC-V). >>> The only use that is uapi is the *default* length of the command line if the kernel header doesn't include it (in the case of x86, it is in the bzImage header, but that is atchitecture- or even boot format-specific.) >> Is COMMAND_LINE_SIZE what you call the default length? Does that mean >> that to you the patchset is wrong? > On x86, the COMMAND_LINE_SIZE value is already not part of a uapi header, > but instead (since bzImage format version 2.06) is communicated from > the kernel to the boot loader, which then knows how much data the > kernel will read (at most) from the command line. > > Most x86 kernels these days are booted using UEFI, which I think has > no such interface, the firmware just passes the command line and a > length, but has no way of knowing if the kernel will truncate this. > I think that is the same as with any other architecture that passes > the command line through UEFI, DT or ATAGS, all of which use > length/value pairs. > > Russell argued on IRC that this can be considered an ABI since a > boot loader may use its knowledge of the kernel's command line size > limit to reject long command lines. On the other hand, I don't > think that any boot loader actually does, they just trust that it > fits and don't have a good way of rejecting invalid configuration > other than truncating and/or warning. > > One notable exception I found while looking through is the old > (pre-ATAGS) parameter structure on Arm, which uses COMMAND_LINE_SIZE > as part of the structure definition. Apparently this was deprecated > 22 years ago, so hopefully the remaining riscpc and footbridge > users have all upgraded their bootloaders. > > The only other case I could find that might go wrong is > m68knommu with a few files copying a COMMAND_LINE_SIZE sized > buffer from flash into a kernel buffer: > > arch/m68k/coldfire/m5206.c:void __init config_BSP(char *commandp, int size) > arch/m68k/coldfire/m5206.c-{ > arch/m68k/coldfire/m5206.c-#if defined(CONFIG_NETtel) > arch/m68k/coldfire/m5206.c- /* Copy command line from FLASH to local buffer... */ > arch/m68k/coldfire/m5206.c- memcpy(commandp, (char *) 0xf0004000, size); > arch/m68k/coldfire/m5206.c- commandp[size-1] = 0; > arch/m68k/coldfire/m5206.c-#endif /* CONFIG_NETtel */
I see, thanks your thorough explanation: I don't see this m64k issue as a blocker (unless Geert disagrees but he already reviewed the m64k patches), so I'll send the v5 now.
Thanks again,
Alex
> > Arnd
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