LEB128 decoder and section parsing

src/leb128.inc

@@ -0,0 +1,38 @@
+; esi = pointer to LEB128 bytes
+; eax = decoded value, esi advanced past encoded bytes
+decode_leb128_core:
+	xor	eax, eax
+	xor	ecx, ecx
+.next_byte:
+	movzx	edx, byte [esi]
+	inc	esi
+	mov	bl, dl
+	and	edx, 0x7F
+	shl	edx, cl
+	or	eax, edx
+	add	cl, 7
+	test	bl, 0x80
+	jnz	.next_byte
+	ret
+
+decode_leb128_u32:
+	push	ebx ecx
+	call	decode_leb128_core
+	pop	ecx ebx
+	ret
+
+decode_leb128_s32:
+	push	ebx ecx
+	call	decode_leb128_core
+	cmp	cl, 32
+	jae	.no_extend
+	test	bl, 0x40
+	jz	.no_extend
+	push	edx
+	mov	edx, 0xFFFFFFFF
+	shl	edx, cl
+	or	eax, edx
+	pop	edx
+.no_extend:
+	pop	ecx ebx
+	ret

src/sections.inc

@@ -0,0 +1,68 @@
+SECT_CUSTOM	= 0
+SECT_TYPE	= 1
+SECT_IMPORT	= 2
+SECT_FUNCTION	= 3
+SECT_TABLE	= 4
+SECT_MEMORY	= 5
+SECT_GLOBAL	= 6
+SECT_EXPORT	= 7
+SECT_START	= 8
+SECT_ELEMENT	= 9
+SECT_CODE	= 10
+SECT_DATA	= 11
+SECT_DATACOUNT	= 12
+
+parse_sections:
+	pushad
+	mov	esi, file_buf + WASM_HEADER_SZ
+	mov	edi, file_buf
+	add	edi, [file_size]
+
+.next:
+	cmp	esi, edi
+	jae	.done
+
+	movzx	eax, byte [esi]
+	inc	esi
+	mov	[sec_id], eax
+
+	call	decode_leb128_u32
+	mov	[sec_size], eax
+
+	mov	[sec_content], esi
+	add	eax, esi
+	mov	[sec_next], eax
+
+	push	esi
+	mov	esi, msg_sec_hdr
+	call	print_str
+	mov	eax, [sec_id]
+	call	print_dec
+	call	print_sec_name
+	mov	esi, msg_sec_comma_sz
+	call	print_str
+	mov	eax, [sec_size]
+	call	print_dec
+	mov	esi, msg_bytes
+	call	print_str
+	pop	esi
+
+	mov	esi, [sec_next]
+	jmp	.next
+
+.done:
+	popad
+	ret
+
+print_sec_name:
+	push	esi eax
+	mov	eax, [sec_id]
+	cmp	eax, 12
+	ja	.unknown
+	mov	esi, [sec_name_tbl + eax*4]
+	call	print_str
+	pop	eax esi
+	ret
+.unknown:
+	pop	eax esi
+	ret

src/wasm.asm

@@ -64,6 +64,8 @@ start:
 	mov	esi, msg_bytes
 	call	print_str
 
+	call	parse_sections
+
 	xor	ebx, ebx
 	jmp	.exit
 
@@ -113,6 +115,9 @@ start:
 	mov	eax, SYS_EXIT
 	int	0x80
 
+include 'leb128.inc'
+include 'sections.inc'
+
 ; esi = null-terminated string
 print_str:
 	push	eax ebx ecx edx esi
@@ -200,6 +205,26 @@ msg_size	db 'File size: ', 0
 msg_bytes	db ' bytes', 10, 0
 msg_newline	db 10, 0
 
+msg_sec_hdr	db 'Section ', 0
+msg_sec_comma_sz db ', size: ', 0
+
+sec_name_tbl	dd sn_custom, sn_type, sn_import, sn_func, sn_table
+		dd sn_memory, sn_global, sn_export, sn_start, sn_element
+		dd sn_code, sn_data, sn_datacount
+sn_custom	db ' (Custom)', 0
+sn_type		db ' (Type)', 0
+sn_import	db ' (Import)', 0
+sn_func		db ' (Function)', 0
+sn_table	db ' (Table)', 0
+sn_memory	db ' (Memory)', 0
+sn_global	db ' (Global)', 0
+sn_export	db ' (Export)', 0
+sn_start	db ' (Start)', 0
+sn_element	db ' (Element)', 0
+sn_code		db ' (Code)', 0
+sn_data		db ' (Data)', 0
+sn_datacount	db ' (DataCount)', 0
+
 hex_chars	db '0123456789ABCDEF'
 hex_buf		rb 12
 dec_buf		rb 12
@@ -207,4 +232,9 @@ dec_buf		rb 12
 file_fd		dd 0
 file_size	dd 0
 
+sec_id		dd 0
+sec_size	dd 0
+sec_content	dd 0
+sec_next	dd 0
+
 file_buf	rb FILE_BUF_SIZE

test/run_tests.sh

@@ -28,6 +28,7 @@ check "no arguments"    "Usage:"               $WASM
 check "valid wasm"      "Valid wasm file"       $WASM test/wasm/valid.wasm
 check "bad magic"       "invalid wasm magic"    $WASM test/wasm/badmagic.wasm
 check "bad version"     "unsupported wasm"      $WASM test/wasm/badver.wasm
+check "section list"    "(Type)"                $WASM test/wasm/valid.wasm
 
 echo ""
 echo "Results: $PASS/$TESTS passed, $FAIL failed"