Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 8 Mar 2016 10:29:56 -0800 | Subject | Re: [PATCH] x86/entry: Improve system call entry comments |
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On Mar 8, 2016 2:27 AM, "Ingo Molnar" <mingo@kernel.org> wrote: > > > * Andy Lutomirski <luto@amacapital.net> wrote: > > > > > ENTRY(entry_INT80_32) > > > > > > entry_INT80_32() is only used on pure 32-bit kernels, 64-bit kernels use > > > entry_INT80_compat(). So the above text should not talk about 64-bit programs, as > > > they can never trigger this specific entry point, right? > > > > > > > 64-bit programs can and sometimes do trigger this entry point. [...] > > How can 64-bit programs trigger entry_INT80_32? It's only ever set on 32-bit > kernels: > > #ifdef CONFIG_X86_32 > set_system_trap_gate(IA32_SYSCALL_VECTOR, entry_INT80_32); > set_bit(IA32_SYSCALL_VECTOR, used_vectors); > #endif > > > [...] It does a 32-bit syscall regardless of the caller's bitness, but it > > returns back to the caller's original context, whatever it was. > > That's true of INT $0x80, but I'm talking about the entry point: AFAICS > entry_INT80_32 can only ever execute on 32-bit kernels.
Oh, duh.
> > We don't even build the entry_32.S::entry_INT80_32 entry point on 64-bit kernels: > > obj-y := entry_$(BITS).o [...] > > > > > > So I'd change the explanation to something like: > > > > > > > + * This entry point is active on 32-bit kernels and can thus be used by 32-bit > > > > + * programs to perform 32-bit system calls. (Programs running on 64-bit > > > > + * kernels executing INT $0x80 will land on another entry point: > > > > + * entry_INT80_compat. The ABI is identical.) > > > > I like the part in parentheses. > > So the part in parentheses conflict with your above statement :) > > What I wanted to say with this: > > > > > + * This entry point is active on 32-bit kernels and can thus be used by 32-bit > > > > + * programs to perform 32-bit system calls. (Programs running on 64-bit > > > > + * kernels executing INT $0x80 will land on another entry point: > > > > + * entry_INT80_compat. The ABI is identical.) > > ... is what it says: that entry_INT80_32 is only active on 32-bit kernels, running > 32-bit programs, performing 32-bit system calls. > > Programs running on 64-bit kernels can use INT $0x80 as well, but will land on > another, different, 64-bit kernel specific entry point. > > What am I missing? >
Nothing. I mis-read your earlier email. Want to fix and apply it, or should I send a new version?
> Thanks, > > Ingo
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