On Wed, Jan 25, 2023 at 12:39:26AM -0800, H. Peter Anvin wrote: > > /* Set IP and CX to match so that SYSRET can happen. */ > > ctx->uc_mcontext.gregs[REG_RIP] = rip; > > ctx->uc_mcontext.gregs[REG_RCX] = rip; > > It would be interesting to have the syscall handler try both with and > without this (so it would end up doing both IRET and SYSCALL on legacy.) > Perhaps SIGUSR1 versus SIGUSR2... Just to clarify this more so I am sure I understand it correctly. Did you mean to have the same signal handler without modifiying 'REG_RCX' but still change 'REG_RIP'? IOW, we want to only *remove*: ctx->uc_mcontext.gregs[REG_RCX] = rip; and *keep*: ctx->uc_mcontext.gregs[REG_RIP] = rip; for the SIGUSR2 handler. Thus, inside the entry64 we will jump to the iret path because %rcx != %r11 upon rt_sigreturn()? -- Ammar Faizi
