On Mon, 21 Jun 2021 at 00:11, Alex Ghiti <alex@xxxxxxxx> wrote: > > Hi Palmer, > > Le 23/04/2021 à 04:57, Palmer Dabbelt a écrit : > > On Fri, 02 Apr 2021 11:33:30 PDT (-0700), macro@xxxxxxxxxxx wrote: > >> On Fri, 2 Apr 2021, David Abdurachmanov wrote: > >> > >>> > > > This macro is exported as a part of the user API so it must > >>> not depend on > >>> > > > Kconfig. Also changing it (rather than say adding > >>> COMMAND_LINE_SIZE_V2 or > >>> > > > switching to an entirely new data object that has its dimension > >>> set in a > >>> > > > different way) requires careful evaluation as external binaries > >>> have and > >>> > > > will have the value it expands to compiled in, so it's a part > >>> of the ABI > >>> > > > too. > >>> > > > >>> > > Thanks, I didn't realize this was part of the user BI. In that > >>> case we > >>> > > really can't chage it, so we'll have to sort out some other way > >>> do fix > >>> > > whatever is going on. > >>> > > > >>> > > I've dropped this from fixes. > >>> > > >>> > Does increasing COMMAND_LINE_SIZE break user-space binaries? I would > >>> > expect it to work the same way as adding new enum values, or adding > >>> > fields at the end of versioned structs, etc. > >>> > I would assume the old bootloaders/etc will only support up to the > >>> > old, smaller max command line size, while the kernel will support > >>> > larger command line size, which is fine. > >>> > However, if something copies /proc/cmdline into a fixed-size buffer > >>> > and expects that to work, that will break... that's quite unfortunate > >>> > user-space code... is it what we afraid of? > >>> > > >>> > Alternatively, could expose the same COMMAND_LINE_SIZE, but internally > >>> > support a larger command line? > >>> > >>> Looking at kernel commit history I see PowerPC switched from 512 to > >>> 2048, and I don't see complaints about the ABI on the mailing list. > >>> > >>> If COMMAND_LINE_SIZE is used by user space applications and we > >>> increase it there shouldn't be problems. I would expect things to > >>> work, but just get truncated boot args? That is the application will > >>> continue only to look at the initial 512 chars. > >> > >> The macro is in an include/uapi header, so it's exported to the userland > >> and a part of the user API. I don't know what the consequences are for > >> the RISC-V port specifically, but it has raised my attention, and I think > >> it has to be investigated. > >> > >> Perhaps it's OK to change it after all, but you'd have to go through > >> known/potential users of this macro. I guess there shouldn't be that > >> many > >> of them. > >> > >> In any case it cannot depend on Kconfig, because the userland won't have > >> access to the configuration, and then presumably wants to handle any and > >> all. > > > > It kind of feels to me like COMMAND_LINE_SIZE shouldn't have been part > > of the UABI to begin with. I sent a patch to remove it from the > > asm-generic UABI, let's see if anyone knows of a reason it should be UABI: > > > > https://lore.kernel.org/linux-arch/20210423025545.313965-1-palmer@xxxxxxxxxxx/T/#u > > Arnd seemed to agree with you about removing COMMAND_LINE_SIZE from the > UABI, any progress on your side? Was this ever merged? Don't see this even in linux-next.
