Return "Segmentation fault" when use std instruction

[nick31072002]

Return "Segmentation fault" when use std instruction

[kobalicek]

Here are my comments:

1. JitRuntime already provides a properly setup environment, never do rt._environment.xxx
2. Use error handling and make sure there are no errors.
3. Use logging, creating issues without any kind of log means I cannot really help
4. I think it's undefined behavior to alter the direction flag in a function and to not change it back

So, I'm not sure whether you have encountered error while executing cc.std() or whether you got error after executing the JIT compiled code, please clarify.

[nick31072002]

Hi,

I think my error is after executing the JIT compiled code in LINUX OS, but the same code in WIN10 OS is fine.

Here are my description:

1. JitRuntime already provides a properly setup environment, never do rt._environment.xxx
   -> I want to use X64 instruction, but have no idea how to do it.
   After do "rt._environment.setArch(Arch::kX64);", it's working.
2. Use error handling and make sure there are no errors.
   The error handling didn't show error at this scenario.
3. Use logging, creating issues without any kind of log means I cannot really help
   Log in logger file

  L1:
  nop
  nop
  nop
  std
  nop
  nop
  nop
  L0:
  ret

4. I think it's undefined behavior to alter the direction flag in a function and to not change it back
   Is it means can't use JIT to change CF(direction flag) ?
   I want to test string instrction, so i have to change CF.

[kobalicek]

The requirement is that: "The direction flag DF in the %rFLAGS register must be clear (set to "forward" direction) on function entry and return" - this is specified in ABI.

If you change DF to 1 and exit from function, you have entered the world of undefined behavior and as you see, it will crash when the first instruction that relies on DF==0 is executed.

[nick31072002]

Thank you for the information about DF, it's helpful for me.