[5/5][AArch64, libgcc] Runtime support for AArch64 DWARF operations

[Jiong Wang]

On 11/11/16 18:22, Jiong Wang wrote:
> This patch add AArch64 specific runtime EH unwinding support for
> DW_OP_AARCH64_pauth, DW_OP_AARCH64_paciasp and DW_OP_AARCH64_paciasp_deref.
>
> The semantics of them are described at the specification in patch [1/9].
>
> The support includes:
>    * Parsing these DWARF operations.  Perform unwinding actions according to
>      their semantics.
>
>    * Handling eh_return multi return paths.
>      Function calling __builtin_eh_return (_Unwind_RaiseException*) will have
>      multiple return paths.  One is for normal exit, the other is for install
>      EH handler.  If the _Unwind_RaiseException itself is return address signed,
>      then there will always be return address authentication before return,
>      however, if the return path in _Unwind_RaiseException if from installing EH
>      handler the address of which has already been authenticated during
>      unwinding,  then we need to re-sign that address, so when the execution flow
>      continues at _Unwind_RaiseException's epilogue, the authentication still
>      works correctly.
>
>
> OK for trunk?
>
> libgcc/
> 2016-11-11  Jiong Wang<jiong.wang@arm.com>
>
>          * config/aarch64/unwind-aarch64.c (RA_SIGN_BIT): New flag to indicate
>          one frame is return address signed.
>          (execute_stack_op): Handle DW_OP_AARCH64_pauth, DW_OP_AARCH64_paciasp,
>          DW_OP_AARCH64_paciasp_deref.
>          (uw_init_context): Call aarch64_uw_init_context_1.
>          (uw_init_context_1): Rename to aarch64_uw_init_context_1.  Strip
>          signature for seed address.
>          (uw_install_context): Re-sign handler's address so it works correctly
>          with caller's context.
>          (uw_install_context_1): by_value[LR] can be true, after return address
>          signing LR will come from DWARF value expression rule which is a
>          by_value true rule.
>
>
This is the update on libgcc unwinder support according to new DWARF proposal.

As Joseph commented, duplication of unwind-dw2.c is not encouraged in libgcc,
But from this patch, you can see there are a few places we need to modify for
AArch64 in unwind-aarch64.c, so the file duplication approach is acceptable?


libgcc/

2017-01-06  Jiong Wang  <jiong.wang@arm.com>

         * config/aarch64/unwind-aarch64.c (DWARF_REGNUM_AARCH64_RA_STATE,
         RA_A_SIGNED_BIT): New macros.
         (execute_cfa_program): Multiplex DW_CFA_GNU_window_save on AArch64.
         (uw_frame_state_for): Clear bit[0] of DWARF_REGNUM_AARCH64_RA_STATE.
         (uw_update_context): Authenticate return address according to
         DWARF_REGNUM_AARCH64_RA_STATE.
         (uw_init_context_1): Strip signature of seed address.
         (uw_install_context): Re-authenticate EH handler's address.

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