asmthumb: Fix ubsan diagnostics.

jepler · jepler · commit c458e9fb05cf · 2025-08-29T10:12:36.000-05:00
This fixes the diagnostic "runtime error: left shift of negative
value -1" and ensures the correct instruction is assembled.

Signed-off-by: Jeff Epler &lt;jepler@gmail.com&gt;
diff --git a/py/asmthumb.c b/py/asmthumb.c
@@ -246,7 +246,7 @@ void asm_thumb_mov_reg_reg(asm_thumb_t *as, uint reg_dest, uint reg_src) {
 void asm_thumb_mov_reg_i16(asm_thumb_t *as, uint mov_op, uint reg_dest, int i16_src) {
     assert(reg_dest < ASM_THUMB_REG_R15);
     // mov[wt] reg_dest, #i16_src
-    asm_thumb_op32(as, mov_op | ((i16_src >> 1) & 0x0400) | ((i16_src >> 12) & 0xf), ((i16_src << 4) & 0x7000) | (reg_dest << 8) | (i16_src & 0xff));
+    asm_thumb_op32(as, mov_op | ((i16_src >> 1) & 0x0400) | ((i16_src >> 12) & 0xf), (((uint16_t)i16_src << 4) & 0x7000) | (reg_dest << 8) | (i16_src & 0xff));
 }
 
 static void asm_thumb_mov_rlo_i16(asm_thumb_t *as, uint rlo_dest, int i16_src) {

Original file line number	Diff line number	Diff line change
`@@ -246,7 +246,7 @@ void asm_thumb_mov_reg_reg(asm_thumb_t *as, uint reg_dest, uint reg_src) {`
`246`	`246`	`void asm_thumb_mov_reg_i16(asm_thumb_t *as, uint mov_op, uint reg_dest, int i16_src) {`
`247`	`247`	`assert(reg_dest < ASM_THUMB_REG_R15);`
`248`	`248`	`// mov[wt] reg_dest, #i16_src`
`249`		`- asm_thumb_op32(as, mov_op \| ((i16_src >> 1) & 0x0400) \| ((i16_src >> 12) & 0xf), ((i16_src << 4) & 0x7000) \| (reg_dest << 8) \| (i16_src & 0xff));`
	`249`	`+ asm_thumb_op32(as, mov_op \| ((i16_src >> 1) & 0x0400) \| ((i16_src >> 12) & 0xf), (((uint16_t)i16_src << 4) & 0x7000) \| (reg_dest << 8) \| (i16_src & 0xff));`
`250`	`250`	`}`
`251`	`251`
`252`	`252`	`static void asm_thumb_mov_rlo_i16(asm_thumb_t *as, uint rlo_dest, int i16_src) {`