[PATCH v2 0/8] ELF-FDPIC support for ARM

[Nicolas Pitre]

On Thu, 24 Aug 2017, Mickael GUENE wrote:

> Hi Nicolas,
> 
> > The first one is.
>   It also seems to me that 'Add tls support for cortex-m cpu family'
> patch is missing. There is the one that add the get_tls syscall but
> not this one which enable usage for cortex-m family.

The patch titled "Add tls support for cortex-m cpu family" in your 
repository does 3 things:

- It defines switch_tls to switch_tls_none. Without the patch the 
  default is switch_tls_software. But this has no purpose as on Cortex-M
  targets there is simply no switch_tls usage at all. The switch_tls 
  macro is invoked in entry-armv.S within __switch_to whereas Cortex-M
  uses a different implementation of __switch_to in entry-v7m.S.

- The patch also defines has_tls_reg to 0. That's the same as de default 
  without the patch.

- It also defines tls_emu to 1. That makes no sense as this is for ARMv6 
  that lack the dedicated CP15 register and is completely wrong for 
  Cortex-M. I suspect the actual reason for defining this to 1 was a 
  dubious workaround to prevent set_tls() from storing the TLS value at 
  the absolute address 0xffff0ff0. In recent kernels that particular 
  code is properly conditioned on CONFIG_KUSER_HELPERS instead.

So in the current mainline kernel this patch is useless. This is why I 
didn't consider it.


Nicolas