Are there any powerpc instructions that can read or change the MSR explicitly from user mode? Any that can see or affect the MSR_SE bit?
e.g. x86 has pushf/popf unprivileged instructions, with which a user program can both see the single-step flag set, and enable single-step for its own next instruction (presumably when it has a handler for SIGTRAP). This actually gets used in arcane places. I recall being told before there's no unprivileged way to see or touch MSR_SE. But it looks to me like a user program can set the bit in a sigcontext and sigreturn to set it. Is that intentionally supported? Or could sigreturn ignore the MSR_SE bit without breaking any strange user? On x86 do we some machinations so that PTRACE_GETREGS et al show the single-step bit set if user-mode itself had set it, but not if PTRACE_SINGLESTEP set it. If you use PTRACE_SETREGS et al to set the single-step bit, then it stays set even if you use PTRACE_CONT. I'd like to clean this up for powerpc too. If there is no way at all for user-mode to set MSR_SE, then it doesn't much matter whether it shows up when ptrace reads it--ptrace just needs to ignore attempts to set it. So if there's no reason not to, what I would do is remove MSR_SE from the MSR_DEBUGCHANGE mask and make sigreturn always clear MSR_SE. Does that make sense? Thanks, Roland _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
