Re: [Patch][AArch64] - Error on load pair to same register

[Ryan Mansfield <rmansfield at qnx dot com>]

On 14-11-18 05:14 AM, Richard Earnshaw wrote:
> On 17/11/14 14:57, Ryan Mansfield wrote:
> > 2014-11-17  Ryan Mansfield  <rmansfield@qnx.com>
> >
> >           * config/tc-aarch64.c (md_assemble): Call warn_unpredictable.
> >           (warn_unpredictable): New.
> >
> > 2014-11-17  Ryan Mansfield  <rmansfield@qnx.com>
> >
> >           * gas/aarch64/diagnostic.s: Add new warnings test patterns.
> >           * gas/aarch64/diagnostic.l: Update expected diagnostic output.
>
> Ryan,
>
> Thanks for the patch.
>
> While I can see merit in handling common cases like loads/stores in one
> function, I'm not entirely convinced that having one common function to
> handle all unpredictable insns is a good idea - the function could get
> very big over time with no real gain to be had from the single
> interface.  As such, I'd rename the function to
> warn_unpredictable_ldst() or something like that.
>
> OK with that change.

I've updated the function name, and the comment to be specific for 
load/stores. If this is OK, would someone please apply the patch on my 
behalf? I don't have write privs.

Here are the updated changelogs and patch:

2014-11-18  Ryan Mansfield  <rmansfield@qnx.com>

        * config/tc-aarch64.c (md_assemble): Call warn_unpredictable_ldst.
        (warn_unpredictable_ldst): New.

2014-11-18  Ryan Mansfield  <rmansfield@qnx.com>

        * gas/aarch64/diagnostic.s: Add new warnings test patterns.
        * gas/aarch64/diagnostic.l: Update expected diagnostic output.


Regards,

Ryan Mansfield

diff --git a/gas/config/tc-aarch64.c b/gas/config/tc-aarch64.c
index 8cecfd0..41378f5 100644
--- a/gas/config/tc-aarch64.c
+++ b/gas/config/tc-aarch64.c
@@ -5490,6 +5490,40 @@ programmer_friendly_fixup (aarch64_instruction *instr)
   return TRUE;
 }
 
+/* Check for loads and stores that will cause unpredictable behavior */
+
+static void
+warn_unpredictable_ldst (aarch64_instruction *instr, char *str)
+{
+  aarch64_inst *base = &instr->base;
+  const aarch64_opcode *opcode = base->opcode;
+  const aarch64_opnd_info *opnds = base->operands;
+  switch (opcode->iclass)
+    {
+    case ldst_pos:
+    case ldst_imm9:
+    case ldst_unscaled:
+    case ldst_unpriv:
+      if (opnds[0].reg.regno == opnds[1].reg.regno
+	  && opnds[1].addr.writeback)
+	as_warn (_("unpredictable register after writeback -- `%s'"), str);
+      break;
+    case ldstpair_off:
+    case ldstnapair_offs:
+    case ldstpair_indexed:
+      if ((opnds[0].reg.regno == opnds[2].reg.regno
+	    || opnds[1].reg.regno == opnds[2].reg.regno)
+	  && opnds[2].addr.writeback)
+	    as_warn (_("unpredictable register after writeback -- `%s'"), str);
+      if ((opcode->opcode & (1 << 22))
+	  && opnds[0].reg.regno == opnds[1].reg.regno)
+	    as_warn (_("unpredictable load of register pair -- `%s'"), str);
+      break;
+    default:
+      break;
+    }
+}
+
 /* A wrapper function to interface with libopcodes on encoding and
    record the error message if there is any.
 
@@ -5622,6 +5656,8 @@ md_assemble (char *str)
 	      return;
 	    }
 
+	  warn_unpredictable_ldst (&inst, str);
+
 	  if (inst.reloc.type == BFD_RELOC_UNUSED
 	      || !inst.reloc.need_libopcodes_p)
 	    output_inst (NULL);
diff --git a/gas/testsuite/gas/aarch64/diagnostic.l b/gas/testsuite/gas/aarch64/diagnostic.l
index 322e3c0..d5fdba8 100644
--- a/gas/testsuite/gas/aarch64/diagnostic.l
+++ b/gas/testsuite/gas/aarch64/diagnostic.l
@@ -105,3 +105,12 @@
 [^:]*:109: Error: operand 5 should be an integer register -- `sys #0,c0,c0,#0,kk'
 [^:]*:110: Error: unexpected comma before the omitted optional operand at operand 5 -- `sys #0,c0,c0,#0,'
 [^:]*:112: Error: selected processor does not support `casp w0,w1,w2,w3,\[x4\]'
+[^:]*:115: Warning: unpredictable load of register pair -- `ldp x0,x0,\[sp\]'
+[^:]*:116: Warning: unpredictable load of register pair -- `ldp d0,d0,\[sp\]'
+[^:]*:117: Warning: unpredictable load of register pair -- `ldp x0,x0,\[sp\],#16'
+[^:]*:118: Warning: unpredictable load of register pair -- `ldnp x0,x0,\[sp\]'
+[^:]*:121: Warning: unpredictable register after writeback -- `ldr x0,\[x0,#8\]!'
+[^:]*:122: Warning: unpredictable register after writeback -- `str x0,\[x0,#8\]!'
+[^:]*:123: Warning: unpredictable register after writeback -- `str x1,\[x1\],#8'
+[^:]*:124: Warning: unpredictable register after writeback -- `stp x0,x1,\[x0,#16\]!'
+[^:]*:125: Warning: unpredictable register after writeback -- `ldp x0,x1,\[x1\],#16'
diff --git a/gas/testsuite/gas/aarch64/diagnostic.s b/gas/testsuite/gas/aarch64/diagnostic.s
index b82ac8b..88001da 100644
--- a/gas/testsuite/gas/aarch64/diagnostic.s
+++ b/gas/testsuite/gas/aarch64/diagnostic.s
@@ -110,3 +110,16 @@
 	sys	#0, c0, c0, #0,
 
 	casp w0,w1,w2,w3,[x4]
+
+	# test warning of unpredictable load pairs
+	ldp     x0, x0, [sp]
+	ldp     d0, d0, [sp]
+	ldp     x0, x0, [sp], #16
+	ldnp    x0, x0, [sp]
+
+	# test warning of unpredictable writeback
+	ldr	x0, [x0, #8]!
+	str	x0, [x0, #8]!
+	str	x1, [x1], #8
+	stp	x0, x1, [x0, #16]!
+	ldp	x0, x1, [x1], #16