support pre-assigning indexes for functions that are called indirectly (#616)

This patch adds support for an ".indidx" primitive that pre-assigns table indexes for functions that are called indirectly. It is used by the upstream LLVM WebAssembly backend to support fine-grained control-flow integrity for indirect function calls by emitting instrumentation at each indirect call site to check that the destination index is within certain ranges that correspond to disjoint equivalence classes of indirect call targets. The reason that this primitive is necessary is because the layout of the table section isn't determined until the WebAssembly linker is executed, but indirect function to table index mappings need to be known when opt is executed to generate the correct range checking in the LLVM IR.

2 files changed, 150 insertions, 0 deletions

diff --git a/test/dot_s/indidx.s b/test/dot_s/indidx.s
new file mode 100644
index 000000000..4ebd28af1
--- /dev/null
+++ b/test/dot_s/indidx.s
@@ -0,0 +1,93 @@
+	.text
+	.file	"cfi-wasm.bs.bc"
+	.type	a,@function
+a:                                      # @a
+	.indidx  	3
+	.result 	i32
+# BB#0:                                 # %entry
+	i32.const	$push0=, 0
+                                        # fallthrough-return: $pop0
+	.endfunc
+.Lfunc_end0:
+	.size	a, .Lfunc_end0-a
+
+	.type	b,@function
+b:                                      # @b
+	.indidx  	1
+	.result 	i32
+# BB#0:                                 # %entry
+	i32.const	$push0=, 1
+                                        # fallthrough-return: $pop0
+	.endfunc
+.Lfunc_end1:
+	.size	b, .Lfunc_end1-b
+
+	.type	c,@function
+c:                                      # @c
+	.indidx  	0
+	.result 	i32
+# BB#0:                                 # %entry
+	i32.const	$push0=, 2
+                                        # fallthrough-return: $pop0
+	.endfunc
+.Lfunc_end2:
+	.size	c, .Lfunc_end2-c
+
+	.type	d,@function
+d:                                      # @d
+	.indidx  	2
+	.result 	i32
+# BB#0:                                 # %entry
+	i32.const	$push0=, 3
+                                        # fallthrough-return: $pop0
+	.endfunc
+.Lfunc_end3:
+	.size	d, .Lfunc_end3-d
+
+	.hidden	main
+	.globl	main
+	.type	main,@function
+main:                                   # @main
+	.param  	i32, i32
+	.result 	i32
+	.local  	i32
+# BB#0:                                 # %entry
+	block
+	i32.call	$push1=, getchar@FUNCTION
+	i32.const	$push0=, 2
+	i32.shl 	$push2=, $pop1, $pop0
+	i32.const	$push3=, .Lmain.fp-192
+	i32.add 	$push4=, $pop2, $pop3
+	i32.load	$push9=, 0($pop4)
+	tee_local	$push8=, $2=, $pop9
+	i32.const	$push5=, 4
+	i32.ge_u	$push6=, $pop8, $pop5
+	br_if   	0, $pop6        # 0: down to label0
+# BB#1:                                 # %cont
+	i32.call_indirect	$push7=, $2
+	return  	$pop7
+.LBB4_2:                                # %trap
+	end_block                       # label0:
+	unreachable
+	unreachable
+	.endfunc
+.Lfunc_end4:
+	.size	main, .Lfunc_end4-main
+
+	.type	.Lmain.fp,@object       # @main.fp
+	.section	.data.rel.ro,"aw",@progbits
+	.p2align	4
+.Lmain.fp:
+	.int32	a@FUNCTION
+	.int32	b@FUNCTION
+	.int32	c@FUNCTION
+	.int32	d@FUNCTION
+	.size	.Lmain.fp, 16
+
+	.type	.L__unnamed_1,@object   # @0
+	.section	.rodata,"a",@progbits
+.L__unnamed_1:
+	.size	.L__unnamed_1, 0
+
+
+	.ident	"clang version 3.9.0 (trunk 271314) (llvm/trunk 271322)"
diff --git a/test/dot_s/indidx.wast b/test/dot_s/indidx.wast
new file mode 100644
index 000000000..7d0a56f66
--- /dev/null
+++ b/test/dot_s/indidx.wast
@@ -0,0 +1,57 @@
+(module
+  (memory 1
+    (segment 16 "\03\00\00\00\01\00\00\00\00\00\00\00\02\00\00\00")
+  )
+  (export "memory" memory)
+  (type $FUNCSIG$i (func (result i32)))
+  (import $getchar "env" "getchar" (result i32))
+  (export "main" $main)
+  (export "dynCall_i" $dynCall_i)
+  (table $c $b $d $a)
+  (func $a (type $FUNCSIG$i) (result i32)
+    (i32.const 0)
+  )
+  (func $b (type $FUNCSIG$i) (result i32)
+    (i32.const 1)
+  )
+  (func $c (type $FUNCSIG$i) (result i32)
+    (i32.const 2)
+  )
+  (func $d (type $FUNCSIG$i) (result i32)
+    (i32.const 3)
+  )
+  (func $main (param $0 i32) (param $1 i32) (result i32)
+    (local $2 i32)
+    (block $label$0
+      (br_if $label$0
+        (i32.ge_u
+          (set_local $2
+            (i32.load
+              (i32.add
+                (i32.shl
+                  (call_import $getchar)
+                  (i32.const 2)
+                )
+                (i32.const -176)
+              )
+            )
+          )
+          (i32.const 4)
+        )
+      )
+      (return
+        (call_indirect $FUNCSIG$i
+          (get_local $2)
+        )
+      )
+    )
+    (unreachable)
+    (unreachable)
+  )
+  (func $dynCall_i (param $fptr i32) (result i32)
+    (call_indirect $FUNCSIG$i
+      (get_local $fptr)
+    )
+  )
+)
+;; METADATA: { "asmConsts": {},"staticBump": 32, "initializers": [] }