pkg/compiler: fix incorrect alignment calculation for padding

We assumed that for ConstType alignment is equal to size,
which is perfectly reasonable for normal int8/16/32/64/ptr.
However, padding is also represented by ConstType of arbitrary size,
so if we added 157 bytes of padding that becomes alignment of
the padding field and as the result of the whole struct.
This affects very few structs, but quite radically and quite
important structs.

Discovered thanks to syz-check.

Update #590

2 files changed, 17 insertions, 6 deletions

diff --git a/pkg/compiler/gen.go b/pkg/compiler/gen.go
index bf7b7a46c..4b50958ac 100644
--- a/pkg/compiler/gen.go
+++ b/pkg/compiler/gen.go
@@ -349,15 +349,17 @@ func (comp *compiler) addAlignment(fields []prog.Type, varlen, packed bool, alig
 }
 
 func (comp *compiler) typeAlign(t0 prog.Type) uint64 {
-	switch t0.(type) {
-	case *prog.IntType, *prog.ConstType, *prog.LenType, *prog.FlagsType, *prog.ProcType,
+	switch t := t0.(type) {
+	case *prog.IntType, *prog.LenType, *prog.FlagsType, *prog.ProcType,
 		*prog.CsumType, *prog.PtrType, *prog.VmaType, *prog.ResourceType:
 		return t0.Size()
+	case *prog.ConstType:
+		if t.IsPad {
+			return 1
+		}
+		return t.Size()
 	case *prog.BufferType:
 		return 1
-	}
-
-	switch t := t0.(type) {
 	case *prog.ArrayType:
 		return comp.typeAlign(t.Type)
 	case *prog.StructType:
diff --git a/pkg/compiler/testdata/all.txt b/pkg/compiler/testdata/all.txt
index 7df52dd2f..380d65319 100644
--- a/pkg/compiler/testdata/all.txt
+++ b/pkg/compiler/testdata/all.txt
@@ -256,7 +256,16 @@ s1 {
 	f1	int8
 } [size[C2]]
 
-foo$s0(a ptr[in, s0], b ptr[in, s1])
+s2 {
+	f1	int8
+	f2	s3
+} [size[101]]
+
+s3 {
+	f1	int8
+} [size[100]]
+
+foo$s0(a ptr[in, s0], b ptr[in, s1], c ptr[in, s2])
 
 # Unions.