On Thu, Oct 29, 2020 at 12:55 AM Qing Zhao <qing.z...@oracle.com> wrote:
>
> Hi,
>
> This is the 5th version of the implementation of patch -fzero-call-used-regs.
>
> The major change compared to the previous version (4th version) are:
>
> 1. Documentation change per Richard’s suggestion;
> 2. Use namespace for zero_regs_code;
> 3. Add more general testing cases per Richard’s suggestion;
> 4. I386 part, ST/MM register sets clearing per Uros’s suggestion.
> 5. Add more i386 testing cases for ST/MM clearing per Uros’s suggestion.
> 6. Some minor style fixes.
>
> I have tested this new GCC on both x86 and arm64, no regression.
>
> Please let me know whether it’s ready for stage 1 gcc11?
>
> Thanks.
>
> Qing
>
> ******The documentation (gcc.info):
> 'zero_call_used_regs ("CHOICE")'
>
> The 'zero_call_used_regs' attribute causes the compiler to zero a
> subset of all call-used registers at function return according to
> CHOICE. This is used to increase the program security by either
> mitigating Return-Oriented Programming (ROP) or preventing
> information leak through registers.
>
> A "call-used" register is a register whose contents can be changed
> by a function call; therefore, a caller cannot assume that the
> register has the same contents on return from the function as it
> had before calling the function. Such registers are also called
> "call-clobbered", "caller-saved", or "volatile".
>
> In order to satisfy users with different security needs and control
> the run-time overhead at the same time, GCC provides a flexible way
> to choose the subset of the call-used registers to be zeroed.
>
> The three basic values of CHOICE are:
>
> * 'skip' doesn't zero any call-used registers.
>
> * 'used' only zeros call-used registers that are used in the
> function. A "used" register is one whose content has been set
> or referenced in the function.
>
> * 'all' zeros all call-used registers.
>
> In addition to these three basic choices, it is possible to modify
> 'used' or 'all' as follows:
>
> * Adding '-gpr' restricts the zeroing to general-purpose
> registers.
>
> * Adding '-arg' restricts the zeroing to registers that can
> sometimes be used to pass function arguments. This includes
> all argument registers defined by the platform's calling
> conversion, regardless of whether the function uses those
> registers for function arguments or not.
>
> The modifiers can be used individually or together. If they are
> used together, they must appear in the order above.
>
> The full list of CHOICEs is therefore:
>
> * 'skip' doesn't zero any call-used register.
>
> * 'used' only zeros call-used registers that are used in the
> function.
>
> * 'all' zeros all call-used registers.
>
> * 'used-arg' only zeros used call-used registers that pass
> arguments.
>
> * 'used-gpr' only zeros used call-used general purpose
> registers.
>
> * 'used-gpr-arg' only zeros used call-used general purpose
> registers that pass arguments.
>
> * 'all-gpr-arg' zeros all call-used general purpose registers
> that pass arguments.
>
> * 'all-arg' zeros all call-used registers that pass arguments.
>
> * 'all-gpr' zeros all call-used general purpose registers.
>
> Among this list, 'used-gpr-arg', 'used-arg', 'all-gpr-arg', and
> 'all-arg' are mainly used for ROP mitigation.
>
> The default for the attribute is controlled by
> '-fzero-call-used-regs’.
>
> '-fzero-call-used-regs=CHOICE'
> Zero call-used registers at function return to increase the program
> security by either mitigating Return-Oriented Programming (ROP) or
> preventing information leak through registers.
>
> The possible values of CHOICE are the same as for the
> 'zero_call_used_regs' attribute (*note Function Attributes::). The
> default is 'skip'.
>
> You can control this behavior for a specific function by using the
> function attribute 'zero_call_used_regs' (*note Function
> Attributes::).
>
> ******The changelog:
>
> gcc/ChangeLog:
>
> 2020-10-28 Qing Zhao <qing.z...@oracle.com>
> H.J.Lu <hjl.to...@gmail.com>
>
> * common.opt: Add new option -fzero-call-used-regs
> * config/i386/i386.c (zero_call_used_regno_p): New function.
> (zero_call_used_regno_mode): Likewise.
> (zero_all_vector_registers): Likewise.
> (zero_all_st_registers): Likewise.
> (zero_all_mm_registers): Likewise.
> (ix86_zero_call_used_regs): Likewise.
> (TARGET_ZERO_CALL_USED_REGS): Define.
> * df-scan.c (df_epilogue_uses_p): New function.
> (df_get_exit_block_use_set): Replace EPILOGUE_USES with
> df_epilogue_uses_p.
> * df.h (df_epilogue_uses_p): Declare.
> * doc/extend.texi: Document the new zero_call_used_regs attribute.
> * doc/invoke.texi: Document the new -fzero-call-used-regs option.
> * doc/tm.texi: Regenerate.
> * doc/tm.texi.in (TARGET_ZERO_CALL_USED_REGS): New hook.
> * emit-rtl.h (struct rtl_data): New fields zero_call_used_regs
> and must_be_zero_on_return.
> * flag-types.h (namespace zero_regs_code): New namespace.
> * function.c (gen_call_used_regs_seq): New function.
> (class pass_zero_call_used_regs): New class.
> (pass_zero_call_used_regs::execute): New function.
> (make_pass_zero_call_used_regs): New function.
> * optabs.c (expand_asm_reg_clobber_mem_blockage): New function.
> * optabs.h (expand_asm_reg_clobber_mem_blockage): Declare.
> * opts.c (zero_call_used_regs_opts): New structure array
> initialization.
> (parse_zero_call_used_regs_options): New function.
> (common_handle_option): Handle fzero-call-used-regs.
> * opts.h (zero_call_used_regs_opts): New structure array.
> * passes.def: Add new pass pass_zero_call_used_regs.
> * recog.c (valid_insn_p): New function.
> * recog.h (valid_insn_p): Declare.
> * resource.c (init_resource_info): Replace EPILOGUE_USES with
> df_epilogue_uses_p.
> * target.def (zero_call_used_regs): New hook.
> * targhooks.c (default_zero_call_used_regs): New function.
> * targhooks.h (default_zero_call_used_regs): Declare.
> * tree-pass.h (make_pass_zero_call_used_regs): Declare.
>
> gcc/c-family/ChangeLog:
>
> 2020-10-28 Qing Zhao <qing.z...@oracle.com>
> H.J.Lu <hjl.to...@gmail.com>
>
> * c-attribs.c (c_common_attribute_table): Add new attribute
> zero_call_used_regs.
> (handle_zero_call_used_regs_attribute): New function.
>
> gcc/testsuite/ChangeLog:
>
> 2020-10-28 Qing Zhao <qing.z...@oracle.com>
> H.J.Lu <hjl.to...@gmail.com>
>
> * c-c++-common/zero-scratch-regs-1.c: New test.
> * c-c++-common/zero-scratch-regs-10.c: New test.
> * c-c++-common/zero-scratch-regs-11.c: New test.
> * c-c++-common/zero-scratch-regs-2.c: New test.
> * c-c++-common/zero-scratch-regs-3.c: New test.
> * c-c++-common/zero-scratch-regs-4.c: New test.
> * c-c++-common/zero-scratch-regs-5.c: New test.
> * c-c++-common/zero-scratch-regs-6.c: New test.
> * c-c++-common/zero-scratch-regs-7.c: New test.
> * c-c++-common/zero-scratch-regs-8.c: New test.
> * c-c++-common/zero-scratch-regs-9.c: New test.
> * c-c++-common/zero-scratch-regs-attr-usages.c: New test.
> * gcc.target/i386/zero-scratch-regs-1.c: New test.
> * gcc.target/i386/zero-scratch-regs-10.c: New test.
> * gcc.target/i386/zero-scratch-regs-11.c: New test.
> * gcc.target/i386/zero-scratch-regs-12.c: New test.
> * gcc.target/i386/zero-scratch-regs-13.c: New test.
> * gcc.target/i386/zero-scratch-regs-14.c: New test.
> * gcc.target/i386/zero-scratch-regs-15.c: New test.
> * gcc.target/i386/zero-scratch-regs-16.c: New test.
> * gcc.target/i386/zero-scratch-regs-17.c: New test.
> * gcc.target/i386/zero-scratch-regs-18.c: New test.
> * gcc.target/i386/zero-scratch-regs-19.c: New test.
> * gcc.target/i386/zero-scratch-regs-2.c: New test.
> * gcc.target/i386/zero-scratch-regs-20.c: New test.
> * gcc.target/i386/zero-scratch-regs-21.c: New test.
> * gcc.target/i386/zero-scratch-regs-22.c: New test.
> * gcc.target/i386/zero-scratch-regs-23.c: New test.
> * gcc.target/i386/zero-scratch-regs-24.c: New test.
> * gcc.target/i386/zero-scratch-regs-25.c: New test.
> * gcc.target/i386/zero-scratch-regs-26.c: New test.
> * gcc.target/i386/zero-scratch-regs-27.c: New test.
> * gcc.target/i386/zero-scratch-regs-28.c: New test.
> * gcc.target/i386/zero-scratch-regs-29.c: New test.
> * gcc.target/i386/zero-scratch-regs-30.c: New test.
> * gcc.target/i386/zero-scratch-regs-31.c: New test.
> * gcc.target/i386/zero-scratch-regs-3.c: New test.
> * gcc.target/i386/zero-scratch-regs-4.c: New test.
> * gcc.target/i386/zero-scratch-regs-5.c: New test.
> * gcc.target/i386/zero-scratch-regs-6.c: New test.
> * gcc.target/i386/zero-scratch-regs-7.c: New test.
> * gcc.target/i386/zero-scratch-regs-8.c: New test.
> * gcc.target/i386/zero-scratch-regs-9.c: New test.
OK for x86 part.
Thanks,
Uros.
