Asan changes for RISC-V.

We have only riscv64 asan support, there is no riscv32 support as yet.  So I
need to be able to conditionally enable asan support for the riscv target.  I
implemented this by returning zero from the asan_shadow_offset function.  This
requires a change to toplev.c and docs in target.def.

	gcc/
	* config/riscv/riscv.c (riscv_asan_shadow_offset): New.
	(TARGET_ASAN_SHADOW_OFFSET): New.
	* doc/tm.texi: Regenerated.
	* target.def (asan_shadow_offset); Mention that it can return zero.
	* toplev.c (process_options): Check for and handle zero return from
	targetm.asan_shadow_offset call.

Co-Authored-By: cooper.joshua <cooper.joshua@linux.alibaba.com>

gcc/config/riscv/riscv.c

@@ -5299,6 +5299,19 @@ riscv_gpr_save_operation_p (rtx op)
   return true;
 }
 
+/* Implement TARGET_ASAN_SHADOW_OFFSET.  */
+
+static unsigned HOST_WIDE_INT
+riscv_asan_shadow_offset (void)
+{
+  /* We only have libsanitizer support for RV64 at present.
+
+     This number must match kRiscv*_ShadowOffset* in the file
+     libsanitizer/asan/asan_mapping.h which is currently 1<<29 for rv64,
+     even though 1<<36 makes more sense.  */
+  return TARGET_64BIT ? (HOST_WIDE_INT_1 << 29) : 0;
+}
+
 /* Initialize the GCC target structure.  */
 #undef TARGET_ASM_ALIGNED_HI_OP
 #define TARGET_ASM_ALIGNED_HI_OP "\t.half\t"
@@ -5482,6 +5495,9 @@ riscv_gpr_save_operation_p (rtx op)
 #undef TARGET_NEW_ADDRESS_PROFITABLE_P
 #define TARGET_NEW_ADDRESS_PROFITABLE_P riscv_new_address_profitable_p
 
+#undef TARGET_ASAN_SHADOW_OFFSET
+#define TARGET_ASAN_SHADOW_OFFSET riscv_asan_shadow_offset
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-riscv.h"

gcc/doc/tm.texi

@@ -12094,7 +12094,8 @@ is zero, which disables this optimization.
 @deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_ASAN_SHADOW_OFFSET (void)
 Return the offset bitwise ored into shifted address to get corresponding
 Address Sanitizer shadow memory address.  NULL if Address Sanitizer is not
-supported by the target.
+supported by the target.  May return 0 if Address Sanitizer is not supported
+by a subtarget.
 @end deftypefn
 
 @deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_MEMMODEL_CHECK (unsigned HOST_WIDE_INT @var{val})

gcc/target.def

@@ -4462,7 +4462,8 @@ DEFHOOK
 (asan_shadow_offset,
  "Return the offset bitwise ored into shifted address to get corresponding\n\
 Address Sanitizer shadow memory address.  NULL if Address Sanitizer is not\n\
-supported by the target.",
+supported by the target.  May return 0 if Address Sanitizer is not supported\n\
+by a subtarget.",
  unsigned HOST_WIDE_INT, (void),
  NULL)
 

gcc/toplev.c

@@ -1834,7 +1834,8 @@ process_options (void)
     }
 
   if ((flag_sanitize & SANITIZE_USER_ADDRESS)
-      && targetm.asan_shadow_offset == NULL)
+      && ((targetm.asan_shadow_offset == NULL)
+	  || (targetm.asan_shadow_offset () == 0)))
     {
       warning_at (UNKNOWN_LOCATION, 0,
 		  "%<-fsanitize=address%> not supported for this target");