Do not depend on the evaluation order of C arguments

mame · hsbt · commit fcffed23ada9 · 2024-12-10T10:54:04.000+09:00
The evaluation order of C arguments is unspecified.
`RSTRING_LEN(str)` would fails if the conversion to a String by
`StringValuePtr` is not done yet.

Coverity Scan found this issue.
diff --git a/ext/fiddle/pointer.c b/ext/fiddle/pointer.c
@@ -827,7 +827,8 @@ rb_fiddle_ptr_read_mem(VALUE klass, VALUE address, VALUE len)
 static VALUE
 rb_fiddle_ptr_write_mem(VALUE klass, VALUE addr, VALUE str)
 {
-    memcpy(NUM2PTR(addr), StringValuePtr(str), RSTRING_LEN(str));
+    const char *ptr = StringValuePtr(str);
+    memcpy(NUM2PTR(addr), ptr, RSTRING_LEN(str));
     return str;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -827,7 +827,8 @@ rb_fiddle_ptr_read_mem(VALUE klass, VALUE address, VALUE len)`
`827`	`827`	`static VALUE`
`828`	`828`	`rb_fiddle_ptr_write_mem(VALUE klass, VALUE addr, VALUE str)`
`829`	`829`	`{`
`830`		`- memcpy(NUM2PTR(addr), StringValuePtr(str), RSTRING_LEN(str));`
	`830`	`+ const char *ptr = StringValuePtr(str);`
	`831`	`+ memcpy(NUM2PTR(addr), ptr, RSTRING_LEN(str));`
`831`	`832`	`return str;`
`832`	`833`	`}`
`833`	`834`