Re: [PATCH 06/12] aarch64: fix RTLD_START for BTI

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 05/07/2020 15:49, Adhemerval Zanella wrote:
> On 30/04/2020 14:42, Szabolcs Nagy wrote:
> > From 1e8662264c07e69d807761882e8d77f0916ae562 Mon Sep 17 00:00:00 2001
> > From: Szabolcs Nagy <szabolcs.nagy@arm.com>
> > Date: Tue, 31 Mar 2020 17:32:14 +0100
> > Subject: [PATCH 06/12] aarch64: fix RTLD_START for BTI
> > 
> > Tailcalls must use x16 or x17 for the indirect branch instruction
> > to be compatible with code that uses BTI c at function entries.
> > (Other forms of indirect branches can only land on BTI j.)
> > 
> > Also added a BTI c at the ELF entry point of rtld, this is not
> > strictly necessary since the kernel does not use indirect branch
> > to get there, but it seems safest once building glibc itself with
> > BTI is supported.
> 
> LGTM, thanks.
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
> 
> > ---
> >  sysdeps/aarch64/dl-machine.h | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
> > index db3335e5ad..70b9ed3925 100644
> > --- a/sysdeps/aarch64/dl-machine.h
> > +++ b/sysdeps/aarch64/dl-machine.h
> > @@ -125,6 +125,8 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
> >  .globl _dl_start_user							\n\
> >  .type _dl_start_user, %function						\n\
> >  _start:									\n\
> > +	// bti c							\n\
> > +	hint	34							\n\
> 
> This is the BTI_C defined at sysdeps/aarch64/sysdep.h, why can't you use
> it here?

BTI_C is only defined for asm files, but this is inline asm in c.

thanks for the reviews so far, i'm working on a v2 of the patchset
(changing configury bits and how all this is enabled) will post it
when the tests finish running.