Hi

On 02/11/18 18:38, Sudakshina Das wrote:
> Hi
> 
> This patch is part of a series that enables ARMv8.5-A in GCC and
> adds Branch Target Identification Mechanism.
> (https://developer.arm.com/products/architecture/cpu-architecture/a-profile/exploration-tools)
> 
> This patch adds a new pass called "bti" which is triggered by the
> command line argument -mbranch-protection whenever "bti" is turned on.
> 
> The pass iterates through the instructions and adds appropriated BTI
> instructions based on the following:
>      * Add a new "BTI C" at the beginning of a function, unless its already
>        protected by a "PACIASP/PACIBSP". We exempt the functions that are
>        only called directly.
>      * Add a new "BTI J" for every target of an indirect jump, jump table
>        targets, non-local goto targets or labels that might be referenced
>        by variables, constant pools, etc (NOTE_INSN_DELETED_LABEL)
> 
> Since we have already changed the use of indirect tail calls to only x16
> and x17, we do not have to use "BTI JC".
> (check patch 3/6).
> 

I missed out on the explanation for the changes to the trampoline code.
The patch also updates the trampoline code in case BTI is enabled. Since
the trampoline code is a target of an indirect branch, we need to add an
appropriate BTI instruction at the beginning of it to avoid a branch
target exception.

> Bootstrapped and regression tested with aarch64-none-linux-gnu. Added
> new tests.
> Is this ok for trunk?
> 
> Thanks
> Sudi
> 
> *** gcc/ChangeLog ***
> 
> 2018-xx-xx  Sudakshina Das  <sudi.das@arm.com>
> 	    Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
> 
> 	* config.gcc (aarch64*-*-*): Add aarch64-bti-insert.o.
> 	* gcc/config/aarch64/aarch64.h: Update comment for
> 	TRAMPOLINE_SIZE.
> 	* config/aarch64/aarch64.c (aarch64_asm_trampoline_template):
> 	Update if bti is enabled.
> 	* config/aarch64/aarch64-bti-insert.c: New file.
> 	* config/aarch64/aarch64-passes.def (INSERT_PASS_BEFORE): Insert
> 	bti pass.
> 	* config/aarch64/aarch64-protos.h (make_pass_insert_bti):
> 	Declare the new bti pass.
> 	* config/aarch64/aarch64.md (bti_nop): Define.
> 	* config/aarch64/t-aarch64: Add rule for aarch64-bti-insert.o.
> 
> *** gcc/testsuite/ChangeLog ***
> 
> 2018-xx-xx  Sudakshina Das  <sudi.das@arm.com>
> 
> 	* gcc.target/aarch64/bti-1.c: New test.
> 	* gcc.target/aarch64/bti-2.c: New test.
> 	* lib/target-supports.exp
> 	(check_effective_target_aarch64_bti_hw): Add new check for
> 	BTI hw.
>

Updated patch attached with more comments and a bit of simplification
in aarch64-bti-insert.c. ChangeLog still applies.

Thanks
Sudi