Re: [PATCH v3] Add leafy mode for zero-call-used-regs

[Richard Biener <rguenther@suse.de>]

On Mon, 26 Jun 2023, Qing Zhao wrote:

> 
> 
> > On Jun 23, 2023, at 7:27 PM, Alexandre Oliva <oliva@adacore.com> wrote:
> > 
> > On Jun 23, 2023, Qing Zhao via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> > 
> >> It?s better to add this definition earlier in the list of the ?three
> >> basic values?, to make it ?four basic values?, like the following:
> > 
> > Oh, my, sorry for being so dense, I had managed to miss that bit all
> > this time somehow :-(
> > 
> >> The sentence "This value is mainly to provide users a more efficient mode to zero 
> >>    call-used registers in leaf functions.? just for your reference,
> >> the wording can certainly be improved.  -:)
> > 
> > :-)  got it, thanks.  How about this?
> > 
> > 
> > Add leafy mode for zero-call-used-regs
> > 
> > Introduce 'leafy' to auto-select between 'used' and 'all' for leaf and
> > nonleaf functions, respectively.
> > 
> > Regstrapped on x86_64-linux-gnu.  Ok to install?
> 
> LGTM now.
> 
> However, I am not a reviewer,  you might still need approval from a middle-end reviewer.

OK.

> thanks.
> 
> Qing
> 
> 
> > 
> > 
> > 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                                |   30 ++++++++++++++++++--
> > 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, 103 insertions(+), 3 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 852f6b629bea8..739c40368f556 100644
> > --- a/gcc/doc/extend.texi
> > +++ b/gcc/doc/extend.texi
> > @@ -4349,7 +4349,7 @@ through registers.
> > In order to satisfy users with different security needs and control the
> > run-time overhead at the same time, the @var{choice} parameter provides a
> > flexible way to choose the subset of the call-used registers to be zeroed.
> > -The three basic values of @var{choice} are:
> > +The four basic values of @var{choice} are:
> > 
> > @itemize @bullet
> > @item
> > @@ -4362,10 +4362,16 @@ the function.
> > 
> > @item
> > @samp{all} zeros all call-used registers.
> > +
> > +@item
> > +@samp{leafy} behaves like @samp{used} in a leaf function, and like
> > +@samp{all} in a nonleaf function.  This makes for leaner zeroing in leaf
> > +functions, where the set of used registers is known, and that may be
> > +enough for some purposes of register zeroing.
> > @end itemize
> > 
> > In addition to these three basic choices, it is possible to modify
> > -@samp{used} or @samp{all} as follows:
> > +@samp{used}, @samp{all}, and @samp{leafy} as follows:
> > 
> > @itemize @bullet
> > @item
> > @@ -4412,10 +4418,28 @@ 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.
> > +@samp{all-gpr-arg}, @samp{leafy-arg}, and @samp{leafy-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 2e650bf1c487c..0d2dab1b99dd4 100644
> > --- a/gcc/flag-types.h
> > +++ b/gcc/flag-types.h
> > @@ -348,6 +348,7 @@ 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;
> > @@ -356,6 +357,10 @@ 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 6a79a8290f67e..dd2c1136e0725 100644
> > --- a/gcc/function.cc
> > +++ b/gcc/function.cc
> > @@ -5866,6 +5866,9 @@ 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 3087bdac2c6c9..ac81d4e42944d 100644
> > --- a/gcc/opts.cc
> > +++ b/gcc/opts.cc
> > @@ -2115,6 +2115,10 @@ 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>
> 
> 

-- 
Richard Biener <rguenther@suse.de>
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