On March 7, 2016 12:22:28 AM PST, Ingo Molnar <mi...@kernel.org> wrote: > >* Andy Lutomirski <l...@kernel.org> wrote: > >> Ingo suggested that the comments should explain when the various >> entries are used. This adds these explanations and improves other >> parts of the comments. > >Thanks for doing this, this is really useful! > >One very small detail I noticed: > >> +/* >> + * 32-bit legacy system call entry. >> + * >> + * 32-bit x86 Linux system calls traditionally used the INT $0x80 >> + * instruction. INT $0x80 lands here. >> + * >> + * This entry point can be used by 32-bit and 64-bit programs to >perform >> + * 32-bit system calls. Instances of INT $0x80 can be found inline >in >> + * various programs and libraries. It is also used by the vDSO's >> + * __kernel_vsyscall fallback for hardware that doesn't support a >faster >> + * entry method. Restarted 32-bit system calls also fall back to >INT >> + * $0x80 regardless of what instruction was originally used to do >the >> + * system call. >> + * >> + * This is considered a slow path. It is not used by modern libc >> + * implementations on modern hardware except during process startup. >> + * >> + * Arguments: >> + * eax system call number >> + * ebx arg1 >> + * ecx arg2 >> + * edx arg3 >> + * esi arg4 >> + * edi arg5 >> + * ebp arg6 >> + */ >> 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? > >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.) > >Agreed? > >Thanks, > > Ingo
Sadly I believe Android still uses int $0x80 in the upstream version. -- Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.
