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sysprog21 · Nov 21, 2023 · edde5a8 · edde5a8
1 parent e771c22
commit edde5a8
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Showing 3 changed files with 26 additions and 6 deletions.
diff --git a/src/arm-codegen.c b/src/arm-codegen.c
@@ -10,9 +10,9 @@ void emit(int code)
 void cfg_flatten()
 {
     func_t *func = find_func("__syscall");
-    func->fn->bbs->elf_offset = 44;
+    func->fn->bbs->elf_offset = 44; /* offset of start + exit in codegen */
 
-    elf_offset = 80;
+    elf_offset = 80; /* offset of start + exit + syscall in codegen */
     GLOBAL_FUNC.fn->bbs->elf_offset = elf_offset;
 
     ph2_ir_t *ph2_ir;
@@ -37,6 +37,7 @@ void cfg_flatten()
     for (fn = FUNC_LIST.head; fn; fn = fn->next) {
         ph2_ir_t *flatten_ir;
 
+        /* reserve stack */
         flatten_ir = add_ph2_ir(OP_define);
         flatten_ir->src0 = fn->func->stack_size;
 
@@ -171,19 +172,22 @@ void code_generate()
 {
     int elf_data_start = elf_code_start + elf_offset;
 
+    /* start */
     emit(__movw(__AL, __r8, GLOBAL_FUNC.stack_size));
     emit(__movt(__AL, __r8, GLOBAL_FUNC.stack_size));
     emit(__sub_r(__AL, __sp, __sp, __r8));
     emit(__mov_r(__AL, __r12, __sp));
     emit(__bl(__AL, GLOBAL_FUNC.fn->bbs->elf_offset - elf_code_idx));
 
+    /* exit */
     emit(__movw(__AL, __r8, GLOBAL_FUNC.stack_size));
     emit(__movt(__AL, __r8, GLOBAL_FUNC.stack_size));
     emit(__add_r(__AL, __sp, __sp, __r8));
     emit(__mov_r(__AL, __r0, __r0));
     emit(__mov_i(__AL, __r7, 1));
     emit(__svc());
 
+    /* syscall */
     emit(__mov_r(__AL, __r7, __r0));
     emit(__mov_r(__AL, __r0, __r1));
     emit(__mov_r(__AL, __r1, __r2));
@@ -219,6 +223,7 @@ void code_generate()
             abort();
         }
     }
+    /* jump to main */
     emit(__b(__AL, MAIN_BB->elf_offset - elf_code_idx));
 
     int i;

diff --git a/src/cfront.c b/src/cfront.c
@@ -2622,6 +2622,7 @@ basic_block_t *read_body_statement(block_t *parent, basic_block_t *bb)
             lex_expect(T_colon);
 
             if (is_default)
+                /* there's no condition if it is a default label */
                 bb_connect(bb, true_body_, NEXT);
             else
                 bb_connect(bb, true_body_, THEN);
@@ -2644,7 +2645,13 @@ basic_block_t *read_body_statement(block_t *parent, basic_block_t *bb)
                 true_body_ = read_body_statement(parent, true_body_);
                 control = 1;
             }
+
             if (control && true_body_) {
+                /**
+                 * Create a new body block for next case, and connect the last
+                 * body block which lacks `break` to it to make that one ignore
+                 * the upcoming cases.
+                 */
                 basic_block_t *n = bb_create(parent);
                 bb_connect(true_body_, n, NEXT);
                 true_body_ = n;
@@ -2659,9 +2666,13 @@ basic_block_t *read_body_statement(block_t *parent, basic_block_t *bb)
                 if (is_default)
                     error("Label default should be the last one");
 
+                /* create a new conditional block for next case */
                 basic_block_t *n = bb_create(parent);
                 bb_connect(bb, n, ELSE);
                 bb = n;
+
+                /* create a new body block for next case if the last body block
+                 * exits `switch` */
                 if (!true_body_)
                     true_body_ = bb_create(parent);
             } else if (!is_default) {
@@ -2678,6 +2689,7 @@ basic_block_t *read_body_statement(block_t *parent, basic_block_t *bb)
         lex_expect(T_close_curly);
 
         if (true_body_)
+            /* if the last label has no explicit break, connect it to the end */
             bb_connect(true_body_, switch_end, NEXT);
 
         strcpy(var_break->var_name, vd->var_name);

diff --git a/src/riscv-codegen.c b/src/riscv-codegen.c
@@ -10,9 +10,9 @@ void emit(int code)
 void cfg_flatten()
 {
     func_t *func = find_func("__syscall");
-    func->fn->bbs->elf_offset = 32;
+    func->fn->bbs->elf_offset = 32; /* offset of start + exit in codegen */
 
-    elf_offset = 68;
+    elf_offset = 68; /* offset of start + exit + syscall in codegen */
     GLOBAL_FUNC.fn->bbs->elf_offset = elf_offset;
 
     ph2_ir_t *ph2_ir;
@@ -37,6 +37,7 @@ void cfg_flatten()
     for (fn = FUNC_LIST.head; fn; fn = fn->next) {
         ph2_ir_t *flatten_ir;
 
+        /* reserve stack */
         flatten_ir = add_ph2_ir(OP_define);
         flatten_ir->src0 = fn->func->stack_size;
 
@@ -139,18 +140,19 @@ void code_generate()
 {
     int elf_data_start = elf_code_start + elf_offset;
 
+    /* start */
     emit(__addi(__sp, __sp, -GLOBAL_FUNC.stack_size));
     emit(__addi(__gp, __sp, 0));
-
     emit(__jal(__ra, GLOBAL_FUNC.fn->bbs->elf_offset - elf_code_idx));
 
+    /* exit */
     emit(__addi(__gp, __gp, GLOBAL_FUNC.stack_size));
     emit(__addi(__sp, __gp, 0));
-
     emit(__addi(__a0, __a0, 0));
     emit(__addi(__a7, __zero, 93));
     emit(__ecall());
 
+    /* syscall */
     emit(__addi(__a7, __a0, 0));
     emit(__addi(__a0, __a1, 0));
     emit(__addi(__a1, __a2, 0));
@@ -186,6 +188,7 @@ void code_generate()
             abort();
         }
     }
+    /* jump to main */
     emit(__jal(__zero, MAIN_BB->elf_offset - elf_code_idx));
 
     int i;