RE: [PATCH][GCC][AArch64] Ensure that outgoing argument size is at least 8 bytes when alloca and stack-clash. [Patch (3/6)]

[Tamar Christina <Tamar dot Christina at arm dot com>]

Hi All,

I'm sending an updated patch which updates a testcase that  hits one of our corner cases.
This is an assembler scan only update in a testcase.

Regards,
Tamar

> -----Original Message-----
> From: Tamar Christina <tamar.christina@arm.com>
> Sent: Wednesday, July 11, 2018 12:21
> To: gcc-patches@gcc.gnu.org
> Cc: nd <nd@arm.com>; James Greenhalgh <James.Greenhalgh@arm.com>;
> Richard Earnshaw <Richard.Earnshaw@arm.com>; Marcus Shawcroft
> <Marcus.Shawcroft@arm.com>
> Subject: [PATCH][GCC][AArch64] Ensure that outgoing argument size is at
> least 8 bytes when alloca and stack-clash. [Patch (3/6)]
> 
> Hi All,
> 
> This patch adds a requirement that the number of outgoing arguments for a
> function is at least 8 bytes when using stack-clash protection.
> 
> By using this condition we can avoid a check in the alloca code and so have
> smaller and simpler code there.
> 
> A simplified version of the AArch64 stack frames is:
> 
>    +-----------------------+
>    |                       |
>    |                       |
>    |                       |
>    +-----------------------+
>    |LR                     |
>    +-----------------------+
>    |FP                     |
>    +-----------------------+
>    |dynamic allocations    | ----  expanding area which will push the outgoing
>    +-----------------------+       args down during each allocation.
>    |padding                |
>    +-----------------------+
>    |outgoing stack args    | ---- safety buffer of 8 bytes (aligned)
>    +-----------------------+
> 
> By always defining an outgoing argument, alloca(0) effectively is safe to
> probe at $sp due to the reserved buffer being there.  It will never corrupt the
> stack.
> 
> This is also safe for alloca(x) where x is 0 or x % page_size == 0.  In the former
> it is the same case as alloca(0) while the latter is safe because any allocation
> pushes the outgoing stack args down:
> 
>    |FP                     |
>    +-----------------------+
>    |                       |
>    |dynamic allocations    | ----  alloca (x)
>    |                       |
>    +-----------------------+
>    |padding                |
>    +-----------------------+
>    |outgoing stack args    | ---- safety buffer of 8 bytes (aligned)
>    +-----------------------+
> 
> Which means when you probe for the residual, if it's 0 you'll again just probe
> in the outgoing stack args range, which we know is non-zero (at least 8 bytes).
> 
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> Target was tested with stack clash on and off by default.
> 
> Ok for trunk?
> 
> Thanks,
> Tamar
> 
> gcc/
> 2018-07-11  Tamar Christina  <tamar.christina@arm.com>
> 
> 	PR target/86486
> 	* config/aarch64/aarch64.h (STACK_CLASH_OUTGOING_ARGS,
> 	STACK_DYNAMIC_OFFSET): New.
> 	* config/aarch64/aarch64.c (aarch64_layout_frame):
> 	Update outgoing args size.
> 	(aarch64_stack_clash_protection_alloca_probe_range,
> 	TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE):
> New.
> 
> gcc/testsuite/
> 2018-07-11  Tamar Christina  <tamar.christina@arm.com>
> 
> 	PR target/86486
> 	* gcc.target/aarch64/stack-check-alloca-1.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-10.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-2.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-3.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-4.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-5.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-6.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-7.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-8.c: New.
> 	* gcc.target/aarch64/stack-check-alloca-9.c: New.
> 	* gcc.target/aarch64/stack-check-alloca.h: New.
> 	* gcc.target/aarch64/stack-check-14.c: New.
> 	* gcc.target/aarch64/stack-check-15.c: New.
> 
> --

diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 1345f0eb171d05e2b833935c0a32f79c3db03f99..e9560b53bd8b5761855561dbf82d9c90cc1c282a 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -88,6 +88,10 @@
    before probing has to be done for stack clash protection.  */
 #define STACK_CLASH_CALLER_GUARD 1024
 
+/* This value represents the minimum amount of bytes we expect the function's
+   outgoing arguments to be when stack-clash is enabled.  */
+#define STACK_CLASH_OUTGOING_ARGS 8
+
 /* This value controls how many pages we manually unroll the loop for when
    generating stack clash probes.  */
 #define STACK_CLASH_MAX_UNROLL_PAGES 4
@@ -1069,4 +1073,15 @@ extern poly_uint16 aarch64_sve_vg;
 
 #define REGMODE_NATURAL_SIZE(MODE) aarch64_regmode_natural_size (MODE)
 
+/* Allocate the minimum of STACK_CLASH_OUTGOING_ARGS if stack clash protection
+   is enabled for the outgoing arguments.  This is essential as the extra args
+   space allows if to skip a check in alloca.  */
+#undef STACK_DYNAMIC_OFFSET
+#define STACK_DYNAMIC_OFFSET(FUNDECL)					   \
+   ((flag_stack_clash_protection					   \
+     && cfun->calls_alloca						   \
+     && known_lt (crtl->outgoing_args_size, STACK_CLASH_OUTGOING_ARGS))    \
+    ? ROUND_UP (STACK_CLASH_OUTGOING_ARGS, STACK_BOUNDARY / BITS_PER_UNIT) \
+    : (crtl->outgoing_args_size + STACK_POINTER_OFFSET))
+
 #endif /* GCC_AARCH64_H */
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 7c5daf2c62eaeeb1f066d4f2828197b98d31f158..e74a4144bdf64a66f04789421e245deea6204b13 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -4043,6 +4043,10 @@ aarch64_layout_frame (void)
 
   cfun->machine->frame.emit_frame_chain = aarch64_needs_frame_chain ();
 
+  /* Adjust the outgoing arguments size if required.  Keep it in sync with what
+     the mid-end is doing.  */
+  crtl->outgoing_args_size = STACK_DYNAMIC_OFFSET (cfun);
+
 #define SLOT_NOT_REQUIRED (-2)
 #define SLOT_REQUIRED     (-1)
 
@@ -4810,6 +4814,16 @@ aarch64_set_handled_components (sbitmap components)
       cfun->machine->reg_is_wrapped_separately[regno] = true;
 }
 
+/* On AArch64 we have an ABI defined safe buffer for which we have to do no
+   probing.  */
+
+static HOST_WIDE_INT
+aarch64_stack_clash_protection_alloca_probe_range (void)
+{
+  return STACK_CLASH_CALLER_GUARD;
+}
+
+
 /* Allocate POLY_SIZE bytes of stack space using TEMP1 and TEMP2 as scratch
    registers.  If POLY_SIZE is not large enough to require a probe this function
    will only adjust the stack.  When allocation the stack space
@@ -18359,6 +18373,10 @@ aarch64_libgcc_floating_mode_supported_p
 #undef TARGET_CONSTANT_ALIGNMENT
 #define TARGET_CONSTANT_ALIGNMENT aarch64_constant_alignment
 
+#undef TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE
+#define TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE \
+  aarch64_stack_clash_protection_alloca_probe_range
+
 #undef TARGET_COMPUTE_PRESSURE_CLASSES
 #define TARGET_COMPUTE_PRESSURE_CLASSES aarch64_compute_pressure_classes
 
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-14.c b/gcc/testsuite/gcc.target/aarch64/stack-check-14.c
new file mode 100644
index 0000000000000000000000000000000000000000..a573d108a0ce0243e038411aa01eb65dfd81a460
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-14.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+int t1(int);
+
+int t2(int x)
+{
+  char *p = __builtin_alloca (4050);
+  x = t1 (x);
+  return p[x];
+}
+
+
+/* This test has a constant sized alloca that is smaller than the
+   probe interval.  Only one probe is required since the value is larger
+   than 1024 bytes but smaller than 63k.
+
+   The form can change quite a bit so we just check for two
+   probes without looking at the actual address.  */
+/* { dg-final { scan-assembler-times "str\\txzr," 1 } } */
+
+
+
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-15.c b/gcc/testsuite/gcc.target/aarch64/stack-check-15.c
new file mode 100644
index 0000000000000000000000000000000000000000..497d83e6596a3cbfce898ca6cda1a65d5fe76d0b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-15.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+int t1(int);
+
+int t2(int x)
+{
+  char *p = __builtin_alloca (x);
+  x = t1 (x);
+  return p[x];
+}
+
+
+/* This test has a variable sized alloca.  It requires 3 probes.
+   One in the loop, one for the residual, one for when it's < 1024 and one for
+   when it's not.
+
+   The form can change quite a bit so we just check for two
+   probes without looking at the actual address.  */
+/* { dg-final { scan-assembler-times "str\\txzr," 3 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-1.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..524713a2c17f51eef0c58851661f9275f24212c9
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-1.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE y
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 2 } } */
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp\]} 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-10.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-10.c
new file mode 100644
index 0000000000000000000000000000000000000000..24553daf9eedd372c1766b884fd48bebd42de9b2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-10.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 127.5 * 64 * 1024
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 2 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-2.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..086fa86a4d2d6bffdca6474afa93c6a508000d58
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-2.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 0
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-not {str\s+xzr,} } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-3.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..f5c20dad7ace049da0da6bfaafb5ec5e0b985e6e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-3.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 100
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 8\]} 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-4.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..729d1184bc981a7fb00bc14d118ef526f96360b8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-4.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 2 * 1024
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-5.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-5.c
new file mode 100644
index 0000000000000000000000000000000000000000..2c08aa13dcf5cee5fedbd931535ae2776e422ad6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-5.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 63 * 1024
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-6.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-6.c
new file mode 100644
index 0000000000000000000000000000000000000000..2881e9666cebb1f5f3d5867d23ade5d4b9d8366c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-6.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 63.5 * 1024
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-7.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-7.c
new file mode 100644
index 0000000000000000000000000000000000000000..60f91c1c4dbc13c6f281e5d9ff2d89688dc942c7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-7.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 64 * 1024
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 1 } } */
+
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-8.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-8.c
new file mode 100644
index 0000000000000000000000000000000000000000..07bf2e6d9abc65b211f4e128fae432d68d7be8d5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-8.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 65 * 1024
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 1 } } */
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 8\]} 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-9.c b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-9.c
new file mode 100644
index 0000000000000000000000000000000000000000..4b4da189b782c61438715bf5a8f0b791de4e29dd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca-9.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection --param stack-clash-protection-guard-size=16" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+#define SIZE 127 * 64 * 2014
+#include "stack-check-alloca.h"
+
+/* { dg-final { scan-assembler-times {str\s+xzr, \[sp, 1024\]} 2 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-alloca.h b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4f7fa2dd351cc7b76784103fc645a066c5ba6e3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-alloca.h
@@ -0,0 +1,13 @@
+#include <alloca.h>
+
+__attribute__((noinline, noipa))
+void g (char* ptr, int y)
+{
+  ptr[y] = '\0';
+}
+
+void f_caller (int y)
+{
+  char* pStr = alloca(SIZE);
+  g (pStr, y);
+}
\ No newline at end of file