Re: [PATCH 3/7, GCC, ARM, V8M] ARMv8-M Security Extension's cmse_nonsecure_entry: __acle_se label and bxns return

["Andre Vieira (lists)" <Andre.SimoesDiasVieira@arm.com>]

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On 26/10/16 11:03, Kyrill Tkachov wrote:
> Hi Andre,
> 
> On 25/10/16 17:28, Andre Vieira (lists) wrote:
>> On 25/07/16 14:23, Andre Vieira (lists) wrote:
>>> This patch extends support for the ARMv8-M Security Extensions
>>> 'cmse_nonsecure_entry' attribute in two ways:
>>>
>>> 1) Generate two labels for the function, the regular function name and
>>> one with the function's name appended to '__acle_se_', this will trigger
>>> the linker to create a secure gateway veneer for this entry function.
>>> 2) Return from cmse_nonsecure_entry marked functions using bxns.
>>>
>>> See Section 5.4 of ARM®v8-M Security Extensions
>>> (http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/index.html).
>>>
>>>
>>>
>>> *** gcc/ChangeLog ***
>>> 2016-07-25  Andre Vieira        <andre.simoesdiasvieira@arm.com>
>>>              Thomas Preud'homme  <thomas.preudhomme@arm.com>
>>>
>>>          * config/arm/arm.c (use_return_insn): Change to return with 
>>> bxns
>>>          when cmse_nonsecure_entry.
>>>          (output_return_instruction): Likewise.
>>>          (arm_output_function_prologue): Likewise.
>>>          (thumb_pop): Likewise.
>>>          (thumb_exit): Likewise.
>>>          (arm_function_ok_for_sibcall): Disable sibcall for entry
>>> functions.
>>>          (arm_asm_declare_function_name): New.
>>>          * config/arm/arm-protos.h (arm_asm_declare_function_name): New.
>>>          * config/arm/elf.h (ASM_DECLARE_FUNCTION_NAME): Redefine to
>>>          use arm_asm_declare_function_name.
>>>
>>> *** gcc/testsuite/ChangeLog ***
>>> 2016-07-25  Andre Vieira        <andre.simoesdiasvieira@arm.com>
>>>              Thomas Preud'homme  <thomas.preudhomme@arm.com>
>>>
>>>          * gcc.target/arm/cmse/cmse-2.c: New.
>>>          * gcc.target/arm/cmse/cmse-4.c: New.
>>>
>> Hi,
>>
>> Rebased previous patch on top of trunk as requested. No changes to
>> ChangeLog.
>>
>> Cheers,
>> Andre
> 
> @@ -19919,6 +19932,42 @@ output_return_instruction (rtx operand, bool
> really_return, bool reverse,
>    return "";
>  }
>  
> +/* Output in FILE asm statements needed to declare the NAME of the
> function
> +   defined by its DECL node.  */
> +
> +void
> +arm_asm_declare_function_name (FILE *file, const char *name, tree decl)
> +{
> +  size_t cmse_name_len;
> +  char *cmse_name = 0;
> +  char cmse_prefix[] = "__acle_se_";
> +
> +  if (use_cmse && lookup_attribute ("cmse_nonsecure_entry",
> +                    DECL_ATTRIBUTES (decl)))
> +    {
> +      cmse_name_len = sizeof (cmse_prefix) + strlen (name);
> +      cmse_name = XALLOCAVEC (char, cmse_name_len);
> +      snprintf (cmse_name, cmse_name_len, "%s%s", cmse_prefix, name);
> +      targetm.asm_out.globalize_label (file, cmse_name);
> +    }
> +
> 
> I think this definitely warrants a quick comment explaining why you're
> adding
> __acle_se_ to the function label
> 
>  
>  /* Scan INSN just before assembler is output for it.
> @@ -25247,6 +25301,12 @@ thumb2_expand_return (bool simple_return)
>  
>    if (!simple_return && saved_regs_mask)
>      {
> +      /* TODO: Verify that this path is never taken for
> cmse_nonsecure_entry
> +     functions or adapt code to handle according to ACLE.  This path
> should
> +     not be reachable for cmse_nonsecure_entry functions though we prefer
> +     to guard it for now to ensure that future code changes do not
> silently
> +     change this behavior.  */
> 
> I think you mean s/guard/assert/
> 
>  +      gcc_assert (!IS_CMSE_ENTRY (arm_current_func_type ()));
>        if (num_regs == 1)
>          {
>            rtx par = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (2));
> 
> This is ok with those changes.
> Thanks,
> Kyrill
> 
Hi,

Reworked comments. Also got rid of a redundant 'if (cmse_name)' in
'arm_asm_declare_function_name'. No change to ChangeLogs.

Cheers,
Andre

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diff --git a/gcc/config/arm/arm-protos.h b/gcc/config/arm/arm-protos.h
index e7d9f824596a62f5c99000940f6190ab6aee9255..a9b8326c2770c1f9a9787743cb5faa549e6b7d02 100644
--- a/gcc/config/arm/arm-protos.h
+++ b/gcc/config/arm/arm-protos.h
@@ -31,6 +31,7 @@ extern int arm_volatile_func (void);
 extern void arm_expand_prologue (void);
 extern void arm_expand_epilogue (bool);
 extern void arm_declare_function_name (FILE *, const char *, tree);
+extern void arm_asm_declare_function_name (FILE *, const char *, tree);
 extern void thumb2_expand_return (bool);
 extern const char *arm_strip_name_encoding (const char *);
 extern void arm_asm_output_labelref (FILE *, const char *);
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 40edd3c7fb9567fadfddc36be777fbf53cbb8e9f..fdbdd423236e7388802bc4bd568f260d95485bbe 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -3895,6 +3895,11 @@ use_return_insn (int iscond, rtx sibling)
 	return 0;
     }
 
+  /* ARMv8-M nonsecure entry function need to use bxns to return and thus need
+     several instructions if anything needs to be popped.  */
+  if (saved_int_regs && IS_CMSE_ENTRY (func_type))
+    return 0;
+
   /* If there are saved registers but the LR isn't saved, then we need
      two instructions for the return.  */
   if (saved_int_regs && !(saved_int_regs & (1 << LR_REGNUM)))
@@ -6933,6 +6938,11 @@ arm_function_ok_for_sibcall (tree decl, tree exp)
   if (IS_INTERRUPT (func_type))
     return false;
 
+  /* ARMv8-M non-secure entry functions need to return with bxns which is only
+     generated for entry functions themselves.  */
+  if (IS_CMSE_ENTRY (arm_current_func_type ()))
+    return false;
+
   if (!VOID_TYPE_P (TREE_TYPE (DECL_RESULT (cfun->decl))))
     {
       /* Check that the return value locations are the same.  For
@@ -19768,6 +19778,7 @@ output_return_instruction (rtx operand, bool really_return, bool reverse,
 	 (e.g. interworking) then we can load the return address
 	 directly into the PC.  Otherwise we must load it into LR.  */
       if (really_return
+	  && !IS_CMSE_ENTRY (func_type)
 	  && (IS_INTERRUPT (func_type) || !TARGET_INTERWORK))
 	return_reg = reg_names[PC_REGNUM];
       else
@@ -19908,8 +19919,10 @@ output_return_instruction (rtx operand, bool really_return, bool reverse,
 	  break;
 
 	default:
+	  if (IS_CMSE_ENTRY (func_type))
+	    snprintf (instr, sizeof (instr), "bxns%s\t%%|lr", conditional);
 	  /* Use bx if it's available.  */
-	  if (arm_arch5 || arm_arch4t)
+	  else if (arm_arch5 || arm_arch4t)
 	    sprintf (instr, "bx%s\t%%|lr", conditional);
 	  else
 	    sprintf (instr, "mov%s\t%%|pc, %%|lr", conditional);
@@ -19922,6 +19935,44 @@ output_return_instruction (rtx operand, bool really_return, bool reverse,
   return "";
 }
 
+/* Output in FILE asm statements needed to declare the NAME of the function
+   defined by its DECL node.  */
+
+void
+arm_asm_declare_function_name (FILE *file, const char *name, tree decl)
+{
+  size_t cmse_name_len;
+  char *cmse_name = 0;
+  char cmse_prefix[] = "__acle_se_";
+
+  /* When compiling with ARMv8-M Security Extensions enabled, we should print an
+     extra function label for each function with the 'cmse_nonsecure_entry'
+     attribute.  This extra function label should be prepended with
+     '__acle_se_', telling the linker that it needs to create secure gateway
+     veneers for this function.  */
+  if (use_cmse && lookup_attribute ("cmse_nonsecure_entry",
+				    DECL_ATTRIBUTES (decl)))
+    {
+      cmse_name_len = sizeof (cmse_prefix) + strlen (name);
+      cmse_name = XALLOCAVEC (char, cmse_name_len);
+      snprintf (cmse_name, cmse_name_len, "%s%s", cmse_prefix, name);
+      targetm.asm_out.globalize_label (file, cmse_name);
+
+      ARM_DECLARE_FUNCTION_NAME (file, cmse_name, decl);
+      ASM_OUTPUT_TYPE_DIRECTIVE (file, cmse_name, "function");
+    }
+
+  ARM_DECLARE_FUNCTION_NAME (file, name, decl);
+  ASM_OUTPUT_TYPE_DIRECTIVE (file, name, "function");
+  ASM_DECLARE_RESULT (file, DECL_RESULT (decl));
+  ASM_OUTPUT_LABEL (file, name);
+
+  if (cmse_name)
+    ASM_OUTPUT_LABEL (file, cmse_name);
+
+  ARM_OUTPUT_FN_UNWIND (file, TRUE);
+}
+
 /* Write the function name into the code section, directly preceding
    the function prologue.
 
@@ -19971,10 +20022,6 @@ arm_output_function_prologue (FILE *f, HOST_WIDE_INT frame_size)
 {
   unsigned long func_type;
 
-  /* ??? Do we want to print some of the below anyway?  */
-  if (TARGET_THUMB1)
-    return;
-
   /* Sanity check.  */
   gcc_assert (!arm_ccfsm_state && !arm_target_insn);
 
@@ -20009,6 +20056,8 @@ arm_output_function_prologue (FILE *f, HOST_WIDE_INT frame_size)
     asm_fprintf (f, "\t%@ Nested: function declared inside another function.\n");
   if (IS_STACKALIGN (func_type))
     asm_fprintf (f, "\t%@ Stack Align: May be called with mis-aligned SP.\n");
+  if (IS_CMSE_ENTRY (func_type))
+    asm_fprintf (f, "\t%@ Non-secure entry function: called from non-secure code.\n");
 
   asm_fprintf (f, "\t%@ args = %d, pretend = %d, frame = %wd\n",
 	       crtl->args.size,
@@ -24075,8 +24124,8 @@ thumb_pop (FILE *f, unsigned long mask)
   if (mask & (1 << PC_REGNUM))
     {
       /* Catch popping the PC.  */
-      if (TARGET_INTERWORK || TARGET_BACKTRACE
-	  || crtl->calls_eh_return)
+      if (TARGET_INTERWORK || TARGET_BACKTRACE || crtl->calls_eh_return
+	  || IS_CMSE_ENTRY (arm_current_func_type ()))
 	{
 	  /* The PC is never poped directly, instead
 	     it is popped into r3 and then BX is used.  */
@@ -24137,7 +24186,10 @@ thumb_exit (FILE *f, int reg_containing_return_addr)
       if (crtl->calls_eh_return)
 	asm_fprintf (f, "\tadd\t%r, %r\n", SP_REGNUM, ARM_EH_STACKADJ_REGNUM);
 
-      asm_fprintf (f, "\tbx\t%r\n", reg_containing_return_addr);
+      if (IS_CMSE_ENTRY (arm_current_func_type ()))
+	asm_fprintf (f, "\tbxns\t%r\n", reg_containing_return_addr);
+      else
+	asm_fprintf (f, "\tbx\t%r\n", reg_containing_return_addr);
       return;
     }
   /* Otherwise if we are not supporting interworking and we have not created
@@ -24146,7 +24198,8 @@ thumb_exit (FILE *f, int reg_containing_return_addr)
   else if (!TARGET_INTERWORK
 	   && !TARGET_BACKTRACE
 	   && !is_called_in_ARM_mode (current_function_decl)
-	   && !crtl->calls_eh_return)
+	   && !crtl->calls_eh_return
+	   && !IS_CMSE_ENTRY (arm_current_func_type ()))
     {
       asm_fprintf (f, "\tpop\t{%r}\n", PC_REGNUM);
       return;
@@ -24369,7 +24422,10 @@ thumb_exit (FILE *f, int reg_containing_return_addr)
     asm_fprintf (f, "\tadd\t%r, %r\n", SP_REGNUM, ARM_EH_STACKADJ_REGNUM);
 
   /* Return to caller.  */
-  asm_fprintf (f, "\tbx\t%r\n", reg_containing_return_addr);
+  if (IS_CMSE_ENTRY (arm_current_func_type ()))
+    asm_fprintf (f, "\tbxns\t%r\n", reg_containing_return_addr);
+  else
+    asm_fprintf (f, "\tbx\t%r\n", reg_containing_return_addr);
 }
 \f
 /* Scan INSN just before assembler is output for it.
@@ -25250,6 +25306,12 @@ thumb2_expand_return (bool simple_return)
 
   if (!simple_return && saved_regs_mask)
     {
+      /* TODO: Verify that this path is never taken for cmse_nonsecure_entry
+	 functions or adapt code to handle according to ACLE.  This path should
+	 not be reachable for cmse_nonsecure_entry functions though we prefer
+	 to assert it for now to ensure that future code changes do not silently
+	 change this behavior.  */
+      gcc_assert (!IS_CMSE_ENTRY (arm_current_func_type ()));
       if (num_regs == 1)
         {
           rtx par = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (2));
@@ -25667,6 +25729,7 @@ arm_expand_epilogue (bool really_return)
 
       if (ARM_FUNC_TYPE (func_type) != ARM_FT_INTERWORKED
           && (TARGET_ARM || ARM_FUNC_TYPE (func_type) == ARM_FT_NORMAL)
+	  && !IS_CMSE_ENTRY (func_type)
           && !IS_STACKALIGN (func_type)
           && really_return
           && crtl->args.pretend_args_size == 0
diff --git a/gcc/config/arm/elf.h b/gcc/config/arm/elf.h
index bc4eb86f1da5beabf32647637eb87a3fc17a6c6a..03931eee7390ab4d09522e7d8bea10449719ddba 100644
--- a/gcc/config/arm/elf.h
+++ b/gcc/config/arm/elf.h
@@ -75,16 +75,7 @@
 
 /* We might need a ARM specific header to function declarations.  */
 #undef  ASM_DECLARE_FUNCTION_NAME
-#define ASM_DECLARE_FUNCTION_NAME(FILE, NAME, DECL)		\
-  do								\
-    {								\
-      ARM_DECLARE_FUNCTION_NAME (FILE, NAME, DECL);		\
-      ASM_OUTPUT_TYPE_DIRECTIVE (FILE, NAME, "function");	\
-      ASM_DECLARE_RESULT (FILE, DECL_RESULT (DECL));		\
-      ASM_OUTPUT_LABEL(FILE, NAME);				\
-      ARM_OUTPUT_FN_UNWIND (FILE, TRUE);			\
-    }								\
-  while (0)
+#define ASM_DECLARE_FUNCTION_NAME arm_asm_declare_function_name
 
 /* We might need an ARM specific trailer for function declarations.  */
 #undef  ASM_DECLARE_FUNCTION_SIZE
diff --git a/gcc/testsuite/gcc.target/arm/cmse/cmse-10.c b/gcc/testsuite/gcc.target/arm/cmse/cmse-10.c
new file mode 100644
index 0000000000000000000000000000000000000000..1a91ac39ee37ef20495e047b402d3f5edc60a613
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/cmse/cmse-10.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-mcmse" }  */
+
+void
+foo (void) {}
+
+/* { dg-final { scan-assembler-not "bxns" } } */
+/* { dg-final { scan-assembler "foo:" } } */
+/* { dg-final { scan-assembler-not "__acle_se_foo:" } } */
diff --git a/gcc/testsuite/gcc.target/arm/cmse/cmse-4.c b/gcc/testsuite/gcc.target/arm/cmse/cmse-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..6f930ab04a1097c64097a4e003296bbe85733319
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/cmse/cmse-4.c
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-options "-mcmse" }  */
+
+struct span {
+  int a, b;
+};
+
+extern int qux (void);
+
+void __attribute__ ((cmse_nonsecure_entry))
+foo (void) {}
+
+static void __attribute__ ((cmse_nonsecure_entry))
+bar (void) {} /* { dg-warning "has no effect on functions with static linkage" } */
+
+int __attribute__ ((cmse_nonsecure_entry))
+baz (void)
+{
+  return qux ();
+}
+
+/* { dg-final { scan-assembler-times "bxns" 2 } } */
+/* { dg-final { scan-assembler "foo:" } } */
+/* { dg-final { scan-assembler "__acle_se_foo:" } } */
+/* { dg-final { scan-assembler-not "__acle_se_bar:" } } */
+/* { dg-final { scan-assembler "baz:" } } */
+/* { dg-final { scan-assembler "__acle_se_baz:" } } */
diff --git a/gcc/testsuite/gcc.target/arm/cmse/cmse-9.c b/gcc/testsuite/gcc.target/arm/cmse/cmse-9.c
new file mode 100644
index 0000000000000000000000000000000000000000..1d97f0e1a37209bd129ffe96ce92a86bc2e0d5d1
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/cmse/cmse-9.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-skip-if "Testing exclusion of -mcmse" { arm-*-* } { "-mcmse" } { "" } }  */
+
+
+int __attribute__ ((cmse_nonsecure_entry))
+foo (int a)
+{ /* { dg-warning "attribute ignored without -mcmse option" } */
+  return a + 1;
+}
+
+/* { dg-final { scan-assembler "foo:" } } */
+/* { dg-final { scan-assembler-not "__acle_se_foo:" } } */