Fix some potential unaligned accesses in dtc

Because of the convention of packed representations in property layouts,
it's not uncommon to have integer values in properties which aren't
naturally aligned.  Thus, there are several places in the dtc code where we
cast a potentially unaligned byte pointer into an integer pointer and load
it directly.  On a number of architectures (including sparc64 and arm) this
won't work and will cause a fault.  In some cases it may be trapped and
emulated by the kernel, but not always.

Therefore, replace such direct unaligned reads with a helper which will
handle unaligned data reads (a variant on the fdtXX_ld() functions already
used in libfdt).

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

4 files changed, 38 insertions, 7 deletions

diff --git a/dtc.h b/dtc.h
index 6e74ece..a08f415 100644
--- a/dtc.h
+++ b/dtc.h
@@ -51,6 +51,37 @@ extern int annotate;		/* annotate .dts with input source location */
 
 typedef uint32_t cell_t;
 
+static inline uint16_t dtb_ld16(const void *p)
+{
+	const uint8_t *bp = (const uint8_t *)p;
+
+	return ((uint16_t)bp[0] << 8)
+		| bp[1];
+}
+
+static inline uint32_t dtb_ld32(const void *p)
+{
+	const uint8_t *bp = (const uint8_t *)p;
+
+	return ((uint32_t)bp[0] << 24)
+		| ((uint32_t)bp[1] << 16)
+		| ((uint32_t)bp[2] << 8)
+		| bp[3];
+}
+
+static inline uint64_t dtb_ld64(const void *p)
+{
+	const uint8_t *bp = (const uint8_t *)p;
+
+	return ((uint64_t)bp[0] << 56)
+		| ((uint64_t)bp[1] << 48)
+		| ((uint64_t)bp[2] << 40)
+		| ((uint64_t)bp[3] << 32)
+		| ((uint64_t)bp[4] << 24)
+		| ((uint64_t)bp[5] << 16)
+		| ((uint64_t)bp[6] << 8)
+		| bp[7];
+}
 
 #define streq(a, b)	(strcmp((a), (b)) == 0)
 #define strstarts(s, prefix)	(strncmp((s), (prefix), strlen(prefix)) == 0)
diff --git a/flattree.c b/flattree.c
index bd6977e..07f10d2 100644
--- a/flattree.c
+++ b/flattree.c
@@ -156,7 +156,7 @@ static void asm_emit_data(void *e, struct data d)
 		emit_offset_label(f, m->ref, m->offset);
 
 	while ((d.len - off) >= sizeof(uint32_t)) {
-		asm_emit_cell(e, fdt32_to_cpu(*((fdt32_t *)(d.val+off))));
+		asm_emit_cell(e, dtb_ld32(d.val + off));
 		off += sizeof(uint32_t);
 	}
 
diff --git a/treesource.c b/treesource.c
index c9d980c..2acb920 100644
--- a/treesource.c
+++ b/treesource.c
@@ -110,13 +110,13 @@ static void write_propval_int(FILE *f, const char *p, size_t len, size_t width)
 			fprintf(f, "%02"PRIx8, *(const uint8_t*)p);
 			break;
 		case 2:
-			fprintf(f, "0x%02"PRIx16, fdt16_to_cpu(*(const fdt16_t*)p));
+			fprintf(f, "0x%02"PRIx16, dtb_ld16(p));
 			break;
 		case 4:
-			fprintf(f, "0x%02"PRIx32, fdt32_to_cpu(*(const fdt32_t*)p));
+			fprintf(f, "0x%02"PRIx32, dtb_ld32(p));
 			break;
 		case 8:
-			fprintf(f, "0x%02"PRIx64, fdt64_to_cpu(*(const fdt64_t*)p));
+			fprintf(f, "0x%02"PRIx64, dtb_ld64(p));
 			break;
 		}
 		if (p + width < end)
diff --git a/yamltree.c b/yamltree.c
index 5b6ea8e..4e93c12 100644
--- a/yamltree.c
+++ b/yamltree.c
@@ -59,10 +59,10 @@ static void yaml_propval_int(yaml_emitter_t *emitter, struct marker *markers, ch
 			sprintf(buf, "0x%"PRIx8, *(uint8_t*)(data + off));
 			break;
 		case 2:
-			sprintf(buf, "0x%"PRIx16, fdt16_to_cpu(*(fdt16_t*)(data + off)));
+			sprintf(buf, "0x%"PRIx16, dtb_ld16(data + off));
 			break;
 		case 4:
-			sprintf(buf, "0x%"PRIx32, fdt32_to_cpu(*(fdt32_t*)(data + off)));
+			sprintf(buf, "0x%"PRIx32, dtb_ld32(data + off));
 			m = markers;
 			is_phandle = false;
 			for_each_marker_of_type(m, REF_PHANDLE) {
@@ -73,7 +73,7 @@ static void yaml_propval_int(yaml_emitter_t *emitter, struct marker *markers, ch
 			}
 			break;
 		case 8:
-			sprintf(buf, "0x%"PRIx64, fdt64_to_cpu(*(fdt64_t*)(data + off)));
+			sprintf(buf, "0x%"PRIx64, dtb_ld64(data + off));
 			break;
 		}