From: Mikael Pettersson <mikpe@xxxxxxxx> Date: Fri, 13 Apr 2007 11:23:48 +0200 > Both gcc-4.2.0 and gcc-4.1.2 compile compat_ptr(u32) as a nop, > so it seems that something earlier in the call chain must have > left a sign-extended value in the argument register for `third'. > And true enough, in arch/sparc64/kernel/sys32.S we find that > the entry for sys32_ipc() explicitly sign-extends %o1/%o2/%o3. > %o3 is passed on as-is to `u32 third' in compat_sys_ipc() and > `compat_uptr_t third' in compat_sys_shmat(). > > I don't know the sparc64 ABI rules for how the high 32 bits > of a 64-bit register containing a 32-bit value are supposed > to be (sign-extended, zero-extended, or undefined), but it > seems that u32 values should be zero-extended, which would > make the sign-extension in sys32.S broken. > > At this point I'm lost. I don't even understand how this > could have worked with gcc < 4.2.0, much less where exactly > gcc-4.2.0 broke things. The system call dispatch code for 32-bit syscalls clears the upper 32-bits of all argument registers before calling down into the system call implementations. In your case that would be the sys32.S code. Look at arch/sparc64/kernel/entry.S:linux_sparc_syscall32 where we do the "srl x, 0, y" instructions which clear the upper 32-bits, moving input argument values to the appropriate output argument registers in parallel. The caller is supposed to sign/zero extend arguments, as needed, in the sparc ABI. compat_sys_ipc() is a mess of sign and zero extension, and I'm not surprised there is a bug here :-) I think the fix is to eliminate the sys32.S sys32_ipc entry, and replace the sys32_ipc references in arch/sparc64/kernel/systbls.S with compat_sys_ipc. compat_sys_ipc does all the necessary sign extensions, so if we just use the default zero-extended values the right thing will happen. Could you test that fix? - To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
