Hi

On 13/11/18 14:47, Sudakshina Das wrote:
> 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
> 

I found a missed case in the bti pass and edited the patch to include
it. This made me realize that the only 2 regressions I saw with the
BTI enabled model can now be avoided. (as quoted below from my 6/6
patch)
"Bootstrapped and regression tested with aarch64-none-linux-gnu with
and without the configure option turned on.
Also tested on aarch64-none-elf with and without configure option with a
BTI enabled aem. Only 2 regressions and these were because newlib
requires patches to protect hand coded libraries with BTI."

The ChangeLog still applies.

Sudi