Messages in this thread | | | Subject | Re: [PATCH v3] powerpc/32: remove bogus ppc_select syscall | From | Christophe Leroy <> | Date | Fri, 5 Mar 2021 11:15:52 +0100 |
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Le 05/03/2021 à 11:06, Arnd Bergmann a écrit : > On Fri, Mar 5, 2021 at 9:40 AM Christophe Leroy > <christophe.leroy@csgroup.eu> wrote: >> >> From: Arnd Bergmann <arnd@arndb.de> >> >> The ppc_select function was introduced in linux-2.3.48 in order to support >> code confusing the legacy select() calling convention with the standard one. >> Even 24 years ago, all correctly built code should not have done this and >> could have easily been phased out. Nothing that was compiled later should >> actually try to use the old_select interface, and it would have been broken >> already on all ppc64 kernels with the syscall emulation layer. >> >> This patch brings the 32 bit compat ABI and the native 32 bit ABI for >> powerpc into a consistent state, by removing support for both the >> old_select system call number and the handler for it. > > The description still seems wrong, please drop all the nonsense I wrote > back then and explain what is actually going on. > > This is what I can see from the linux-history tree: > > - The original ppc32 port (linux-1.3.45) had a regular '__NR_select/sys_select' > syscall at #82 and an unusable '__NR__newselect/sys_panic' syscall at #142, > while i386 had the indirect '__NR_select/sys_oldselect' syscall at #82 > and the regular '__NR__newselect/sys_select' version at #142. This was > rather confusing. > > - linux-2.1.48 changed both #82 and #142 to the ppc_select() version that > tries to guess whether the x86 __NR_select/sys_oldselect() behavior or > the regular __NR__newselect/sys_select() behavior is used. > > - linux-2.5.5 added ppc64 support, with a compat version of ppc_select() > on both #82 and #142 that would either use the __NR__newselect/sys_select > semantics or panic() when passed an invalud 'n'. The native ppc64 > port started out with just __NR__newselect/sys_select() on #142 > > - linux-2.5.19 changed ppc64 compat mode to no longer panic(), making > both #82 and #142 behave like __NR__newselect/sys_select(). > > - glibc support for ppc32 gets merged during the linux-2.5 days, supporting > only #142 with the new behavior. > > - linux-2.5.41 dropped support for #82 on ppc64 in compat mode but not > native ppc32. > > - linux-2.6.14 merged the two architecture ports but kept the behavior > unchanged for both. > > - linux-2.6.32 changed the native ppc32 #142 __NR__newselect to > behave the same as compat mode and no longer emulate the > x86 oldselect, but #82 remained unchanged. > > So we have changed behavior multiple times in the past, and the > current state still theoretically allows running non-glibc binaries that > ran on kernels before 2.1.48 that used either the original powerpc > select or the i386 compatible oldselect semantics. Chances are that > those binaries are broken for some other reason now. >
Whaou, nice archeology, thanks. Do you mind if I copy the history you established ?
In your commit, you said 2.3.48. Here in the history you say 2.1.48. Which one is correct ?
Regardless of whethere binaries are broken or not for other reason, is that worth expecting an almost 25 yr old binary to run on future kernels ? If one is able to put the necessary effort to port you hardware to the latest kernel, can't he really port the binary as well ?
Thanks Christophe
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