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?
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>
