Re: [PATCH zero-call-used-regs] Add leafy mode for zero-call-used-regs

[Qing Zhao <qing.zhao@oracle.com>]

Hi, Alexandre,

Could you please explain a little bit on the motivation of this patch first?

thanks.

Qing

> On Oct 21, 2022, at 3:31 AM, Alexandre Oliva <oliva@adacore.com> wrote:
> 
> Introduce 'leafy' to auto-select between 'used' and 'all' for leaf and
> nonleaf functions, respectively.
> 
> Regstrapped on x86_64-linux-gnu.  Ok to install?
> 
> 
> for  gcc/ChangeLog
> 
> 	* doc/extend.texi (zero-call-used-regs): Document leafy and
> 	variants thereof.
> 	* flag-types.h (zero_regs_flags): Add LEAFY_MODE, as well as
> 	LEAFY and variants.
> 	* function.cc (gen_call_ued_regs_seq): Set only_used for leaf
> 	functions in leafy mode.
> 	* opts.cc (zero_call_used_regs_opts): Add leafy and variants.
> 
> for  gcc/testsuite/ChangeLog
> 
> 	* c-c++-common/zero-scratch-regs-leafy-1.c: New.
> 	* c-c++-common/zero-scratch-regs-leafy-2.c: New.
> 	* gcc.target/i386/zero-scratch-regs-leafy-1.c: New.
> 	* gcc.target/i386/zero-scratch-regs-leafy-2.c: New.
> ---
> gcc/doc/extend.texi                                |   22 ++++++++++++++++++--
> gcc/flag-types.h                                   |    5 +++++
> gcc/function.cc                                    |    3 +++
> gcc/opts.cc                                        |    4 ++++
> .../c-c++-common/zero-scratch-regs-leafy-1.c       |   15 ++++++++++++++
> .../c-c++-common/zero-scratch-regs-leafy-2.c       |   21 +++++++++++++++++++
> .../gcc.target/i386/zero-scratch-regs-leafy-1.c    |   12 +++++++++++
> .../gcc.target/i386/zero-scratch-regs-leafy-2.c    |   16 +++++++++++++++
> 8 files changed, 96 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-1.c
> create mode 100644 gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-2.c
> create mode 100644 gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-1.c
> create mode 100644 gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-2.c
> 
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 04af0584d82cc..bf11956c467fb 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -4391,10 +4391,28 @@ zeros all call-used registers that pass arguments.
> @item all-gpr-arg
> zeros all call-used general purpose registers that pass
> arguments.
> +
> +@item leafy
> +Same as @samp{used} in a leaf function, and same as @samp{all} in a
> +nonleaf function.
> +
> +@item leafy-gpr
> +Same as @samp{used-gpr} in a leaf function, and same as @samp{all-gpr}
> +in a nonleaf function.
> +
> +@item leafy-arg
> +Same as @samp{used-arg} in a leaf function, and same as @samp{all-arg}
> +in a nonleaf function.
> +
> +@item leafy-gpr-arg
> +Same as @samp{used-gpr-arg} in a leaf function, and same as
> +@samp{all-gpr-arg} in a nonleaf function.
> +
> @end table
> 
> -Of this list, @samp{used-arg}, @samp{used-gpr-arg}, @samp{all-arg},
> -and @samp{all-gpr-arg} are mainly used for ROP mitigation.
> +Of this list, @samp{used-arg}, @samp{used-gpr-arg}, @samp{leafy-arg},
> +@samp{leafy-gpr-arg}, @samp{all-arg}, and @samp{all-gpr-arg} are mainly
> +used for ROP mitigation.
> 
> The default for the attribute is controlled by @option{-fzero-call-used-regs}.
> @end table
> diff --git a/gcc/flag-types.h b/gcc/flag-types.h
> index d2e751060ffce..b90c85167dcd4 100644
> --- a/gcc/flag-types.h
> +++ b/gcc/flag-types.h
> @@ -338,6 +338,7 @@ namespace zero_regs_flags {
>   const unsigned int ONLY_GPR = 1UL << 2;
>   const unsigned int ONLY_ARG = 1UL << 3;
>   const unsigned int ENABLED = 1UL << 4;
> +  const unsigned int LEAFY_MODE = 1UL << 5;
>   const unsigned int USED_GPR_ARG = ENABLED | ONLY_USED | ONLY_GPR | ONLY_ARG;
>   const unsigned int USED_GPR = ENABLED | ONLY_USED | ONLY_GPR;
>   const unsigned int USED_ARG = ENABLED | ONLY_USED | ONLY_ARG;
> @@ -346,6 +347,10 @@ namespace zero_regs_flags {
>   const unsigned int ALL_GPR = ENABLED | ONLY_GPR;
>   const unsigned int ALL_ARG = ENABLED | ONLY_ARG;
>   const unsigned int ALL = ENABLED;
> +  const unsigned int LEAFY_GPR_ARG = ENABLED | LEAFY_MODE | ONLY_GPR | ONLY_ARG;
> +  const unsigned int LEAFY_GPR = ENABLED | LEAFY_MODE | ONLY_GPR;
> +  const unsigned int LEAFY_ARG = ENABLED | LEAFY_MODE | ONLY_ARG;
> +  const unsigned int LEAFY = ENABLED | LEAFY_MODE;
> }
> 
> /* Settings of flag_incremental_link.  */
> diff --git a/gcc/function.cc b/gcc/function.cc
> index 6474a663b30b8..16582e698041a 100644
> --- a/gcc/function.cc
> +++ b/gcc/function.cc
> @@ -5879,6 +5879,9 @@ gen_call_used_regs_seq (rtx_insn *ret, unsigned int zero_regs_type)
>   only_used = zero_regs_type & ONLY_USED;
>   only_arg = zero_regs_type & ONLY_ARG;
> 
> +  if ((zero_regs_type & LEAFY_MODE) && leaf_function_p ())
> +    only_used = true;
> +
>   /* For each of the hard registers, we should zero it if:
> 	    1. it is a call-used register;
> 	and 2. it is not a fixed register;
> diff --git a/gcc/opts.cc b/gcc/opts.cc
> index ae079fcd20eea..39f6a1b278dc6 100644
> --- a/gcc/opts.cc
> +++ b/gcc/opts.cc
> @@ -2099,6 +2099,10 @@ const struct zero_call_used_regs_opts_s zero_call_used_regs_opts[] =
>   ZERO_CALL_USED_REGS_OPT (all-gpr, zero_regs_flags::ALL_GPR),
>   ZERO_CALL_USED_REGS_OPT (all-arg, zero_regs_flags::ALL_ARG),
>   ZERO_CALL_USED_REGS_OPT (all, zero_regs_flags::ALL),
> +  ZERO_CALL_USED_REGS_OPT (leafy-gpr-arg, zero_regs_flags::LEAFY_GPR_ARG),
> +  ZERO_CALL_USED_REGS_OPT (leafy-gpr, zero_regs_flags::LEAFY_GPR),
> +  ZERO_CALL_USED_REGS_OPT (leafy-arg, zero_regs_flags::LEAFY_ARG),
> +  ZERO_CALL_USED_REGS_OPT (leafy, zero_regs_flags::LEAFY),
> #undef ZERO_CALL_USED_REGS_OPT
>   {NULL, 0U}
> };
> diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-1.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-1.c
> new file mode 100644
> index 0000000000000..c1a0c31ba1c37
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-1.c
> @@ -0,0 +1,15 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -fzero-call-used-regs=leafy" } */
> +
> +volatile int result = 0;
> +int 
> +__attribute__((noipa))
> +foo (int x)
> +{
> +  return x;
> +}
> +int main()
> +{
> +  result = foo (2);
> +  return 0;
> +}
> diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-2.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-2.c
> new file mode 100644
> index 0000000000000..d450620c1fcfe
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-leafy-2.c
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +#include <assert.h>
> +int result = 0;
> +
> +int 
> +__attribute__((noipa))
> +__attribute__ ((zero_call_used_regs("leafy")))
> +foo1 (int x)
> +{
> +  return (x + 1);
> +}
> +
> +int 
> +__attribute__((noipa))
> +__attribute__ ((zero_call_used_regs("leafy")))
> +foo2 (int x)
> +{
> +  return foo1 (x + 2);
> +}
> diff --git a/gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-1.c b/gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-1.c
> new file mode 100644
> index 0000000000000..2277710c771b7
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-1.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fzero-call-used-regs=leafy -fno-stack-protector -fno-PIC" } */
> +
> +void
> +foo (void)
> +{
> +}
> +
> +/* { dg-final { scan-assembler-not "vzeroall" } } */
> +/* { dg-final { scan-assembler-not "%xmm" } } */
> +/* { dg-final { scan-assembler-not "xorl\[ \t\]+%" } } */
> +/* { dg-final { scan-assembler-not "movl\[ \t\]+%" } } */
> diff --git a/gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-2.c b/gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-2.c
> new file mode 100644
> index 0000000000000..24b85c3dbb766
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/zero-scratch-regs-leafy-2.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fzero-call-used-regs=leafy-gpr -fno-stack-protector -fno-PIC" } */
> +
> +extern int bar (int);
> +
> +void
> +foo (void)
> +{
> +  int x = bar (0);
> +  if (x)
> +    bar (1);
> +}
> +
> +/* { dg-final { scan-assembler "xorl\[ \t\]+%eax, %eax" } } */
> +/* { dg-final { scan-assembler "xorl\[ \t\]+%edx, %edx" } } */
> +/* { dg-final { scan-assembler "xorl\[ \t\]+%ecx, %ecx" } } */
> 
> -- 
> Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
>   Free Software Activist                       GNU Toolchain Engineer
> Disinformation flourishes because many people care deeply about injustice
> but very few check the facts.  Ask me about <https://stallmansupport.org>