> On Jun 23, 2023, at 7:27 PM, Alexandre Oliva <ol...@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.
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>
