Re: [RFC PATCH v5 1/2] selftests/x86: sysret_rip: Handle syscall in a FRED system

On Wed, Jan 25, 2023 at 12:39:26AM -0800, H. Peter Anvin wrote:

...

• ret = check_regs_result(ctx->uc_mcontext.gregs[REG_R11],

• 		ctx->uc_mcontext.gregs[REG_RCX],
  

• 		ctx->uc_mcontext.gregs[REG_RBX]);
  

• assert(ret != REGS_ERROR);

This instance, too, needs to be checked against regs_ok_result. It would make most sense to move that handling, and the assert() into check_regs_result() or into a separate function around it.

OK. Sounds better.

...

/* 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...

We will have a new separate patch for that.