From 8e6c2fecfd633171250b7f09ef4aa0328bd5b698 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Thu, 27 Sep 2018 09:09:50 +0930
Subject: [PATCH 1/1] structeq: fix case where we mark padding as unknown.

And change semantics: a negative number means "up to this much padding".

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 ccan/structeq/structeq.h                      |  9 +++--
 .../test/compile_fail-expect-any-padding.c    |  5 ++-
 ...compile_fail-unexpected-negative-padding.c | 20 ++++++++++
 ccan/structeq/test/run-with-unknown-padding.c | 39 +++++++++++++++++++
 4 files changed, 67 insertions(+), 6 deletions(-)
 create mode 100644 ccan/structeq/test/compile_fail-unexpected-negative-padding.c
 create mode 100644 ccan/structeq/test/run-with-unknown-padding.c

diff --git a/ccan/structeq/structeq.h b/ccan/structeq/structeq.h
index 6b90754c..81799539 100644
--- a/ccan/structeq/structeq.h
+++ b/ccan/structeq/structeq.h
@@ -9,14 +9,15 @@
 /**
  * STRUCTEQ_DEF - define an ..._eq function to compare two structures.
  * @sname: name of the structure, and function (<sname>_eq) to define.
- * @padbytes: number of bytes of expected padding, or -1 if unknown.
+ * @padbytes: number of bytes of expected padding, or negative "max".
  * @...: name of every member of the structure.
  *
  * This generates a single memcmp() call in the common case where the
  * structure contains no padding.  Since it can't tell the difference between
  * padding and a missing member, @padbytes can be used to assert that
- * there isn't any, or how many we expect.  -1 means "expect some", since
- * it can be platform dependent.
+ * there isn't any, or how many we expect.  A negative number means
+ * "up to or equal to that amount of padding", as padding can be
+ * platform dependent.
  */
 #define STRUCTEQ_DEF(sname, padbytes, ...)				\
 static inline bool CPPMAGIC_GLUE2(sname, _eq)(const struct sname *_a, \
@@ -25,7 +26,7 @@ static inline bool CPPMAGIC_GLUE2(sname, _eq)(const struct sname *_a, \
 	BUILD_ASSERT(((padbytes) < 0 &&					\
 		      CPPMAGIC_JOIN(+, CPPMAGIC_MAP(STRUCTEQ_MEMBER_SIZE_, \
 						    __VA_ARGS__))	\
-		      > sizeof(*_a))					\
+		      - (padbytes) >= sizeof(*_a))			\
 		     || CPPMAGIC_JOIN(+, CPPMAGIC_MAP(STRUCTEQ_MEMBER_SIZE_, \
 						      __VA_ARGS__))	\
 		     + (padbytes) == sizeof(*_a));			\
diff --git a/ccan/structeq/test/compile_fail-expect-any-padding.c b/ccan/structeq/test/compile_fail-expect-any-padding.c
index 321aef3a..182c8607 100644
--- a/ccan/structeq/test/compile_fail-expect-any-padding.c
+++ b/ccan/structeq/test/compile_fail-expect-any-padding.c
@@ -2,11 +2,12 @@
 
 struct mydata {
 	int start, end;
+	int pad;
 };
 #ifdef FAIL
-#define PADDING -1
+#define PADDING -1 /* We have more than 1 byte padding */
 #else
-#define PADDING 0
+#define PADDING sizeof(int)
 #endif
 
 STRUCTEQ_DEF(mydata, PADDING, start, end);
diff --git a/ccan/structeq/test/compile_fail-unexpected-negative-padding.c b/ccan/structeq/test/compile_fail-unexpected-negative-padding.c
new file mode 100644
index 00000000..2c63b23d
--- /dev/null
+++ b/ccan/structeq/test/compile_fail-unexpected-negative-padding.c
@@ -0,0 +1,20 @@
+#include <ccan/structeq/structeq.h>
+
+struct mydata {
+	int start, end;
+	int pad;
+};
+#ifdef FAIL
+#define PADDING -1
+#else
+#define PADDING -(int)sizeof(int)
+#endif
+
+STRUCTEQ_DEF(mydata, PADDING, start, end);
+
+int main(void)
+{
+	struct mydata a = { 0, 100 };
+
+	return mydata_eq(&a, &a);
+}
diff --git a/ccan/structeq/test/run-with-unknown-padding.c b/ccan/structeq/test/run-with-unknown-padding.c
new file mode 100644
index 00000000..c803e722
--- /dev/null
+++ b/ccan/structeq/test/run-with-unknown-padding.c
@@ -0,0 +1,39 @@
+#include <ccan/structeq/structeq.h>
+#include <ccan/tap/tap.h>
+
+/* In theory, this could be generated without padding, if alignof(int) were 0,
+ * and test would fail.  Call me when that happens. */
+struct mydata {
+	char start;
+	int end;
+};
+
+STRUCTEQ_DEF(mydata, -3, start, end);
+
+struct mydata2 {
+	char start;
+	int end;
+};
+
+STRUCTEQ_DEF(mydata2, -4, start, end);
+
+int main(void)
+{
+	struct mydata a, b;
+
+	/* This is how many tests you plan to run */
+	plan_tests(3);
+
+	a.start = 0;
+	a.end = 100;
+	ok1(mydata_eq(&a, &a));
+
+	b = a;
+	ok1(mydata_eq(&a, &b));
+
+	b.end++;
+	ok1(!mydata_eq(&a, &b));
+
+	/* This exits depending on whether all tests passed */
+	return exit_status();
+}
-- 
2.39.2