clang: mark inline functions unused and add warning options

clang, unlike gcc, will warn on inline functions which are
unused. This can happen if a function is either intended to be used in
the future, or it is only used under certain config options. Mark
those functions with the "unused" attribute; not only does it quiet
the warning, but it also documents it for the user.

Shuffle around the warning options in configure and add a few more
that are specific to clang.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

6 files changed, 88 insertions, 22 deletions

diff --git a/asm/parser.c b/asm/parser.c
index de24103e..3daca0c6 100644
--- a/asm/parser.c
+++ b/asm/parser.c
@@ -234,7 +234,8 @@ static bool parse_braces(decoflags_t *decoflags)
     }
 }
 
-static inline const expr *next_expr(const expr *e, const expr **next_list)
+static inline unused
+const expr *next_expr(const expr *e, const expr **next_list)
 {
     e++;
     if (!e->type) {
diff --git a/asm/preproc.c b/asm/preproc.c
index a2c57883..14ca17d3 100644
--- a/asm/preproc.c
+++ b/asm/preproc.c
@@ -345,7 +345,8 @@ static inline bool tok_text_match(const struct Token *a, const struct Token *b)
     return a->len == b->len && !memcmp(tok_text(a), tok_text(b), a->len);
 }
 
-static inline bool tok_match(const struct Token *a, const struct Token *b)
+static inline unused bool
+tok_match(const struct Token *a, const struct Token *b)
 {
     return a->type == b->type && tok_text_match(a, b);
 }
@@ -763,7 +764,8 @@ static const char *unquote_token_cstr(Token *t)
  * TOK_STRING tokens.
  */
 static Token *quote_any_token(Token *t);
-static inline Token *quote_token(Token *t)
+static inline unused
+Token *quote_token(Token *t)
 {
     if (likely(!tok_is(t, TOK_INTERNAL_STRING)))
 	return t;
diff --git a/config/unconfig.h b/config/unconfig.h
index d01c2b3e..c7d900fc 100644
--- a/config/unconfig.h
+++ b/config/unconfig.h
@@ -60,6 +60,12 @@
 /* Define to 1 if compiled with the `-Wc90-c99-compat' compiler flag */
 /* #undef CFLAGS_WC90_C99_COMPAT */
 
+/* Define to 1 if compiled with the `-Wc99-compat' compiler flag */
+/* #undef CFLAGS_WC99_COMPAT */
+
+/* Define to 1 if compiled with the `-Wc99-extensions' compiler flag */
+/* #undef CFLAGS_WC99_EXTENSIONS */
+
 /* Define to 1 if compiled with the `-Werror' compiler flag */
 /* #undef CFLAGS_WERROR */
 
@@ -225,6 +231,10 @@
    functions */
 /* #undef HAVE_FUNC_ATTRIBUTE_SENTINEL */
 
+/* Define to 1 if your compiler supports __attribute__((unused)) on functions
+   */
+/* #undef HAVE_FUNC_ATTRIBUTE_UNUSED */
+
 /* Define to 1 if your compiler supports __attribute__((alloc_size)) on
    function pointers */
 /* #undef HAVE_FUNC_PTR_ATTRIBUTE1_ALLOC_SIZE */
@@ -265,6 +275,10 @@
    pointers */
 /* #undef HAVE_FUNC_PTR_ATTRIBUTE_SENTINEL */
 
+/* Define to 1 if your compiler supports __attribute__((unused)) on function
+   pointers */
+/* #undef HAVE_FUNC_PTR_ATTRIBUTE_UNUSED */
+
 /* Define to 1 if you have the `getgid' function. */
 /* #undef HAVE_GETGID */
 
@@ -714,6 +728,22 @@
 # endif
 #endif
 
+#ifndef unused_func
+# ifdef HAVE_FUNC_ATTRIBUTE_UNUSED
+#  define unused_func __attribute__((unused))
+# else
+#  define unused_func
+# endif
+#endif
+
+#ifndef unused_func_ptr
+# ifdef HAVE_FUNC_PTR_ATTRIBUTE_UNUSED
+#  define unused_func_ptr __attribute__((unused))
+# else
+#  define unused_func_ptr
+# endif
+#endif
+
 #ifndef never_null
 # ifdef HAVE_FUNC_ATTRIBUTE_RETURNS_NONNULL
 #  define never_null __attribute__((returns_nonnull))
diff --git a/configure.ac b/configure.ac
index 85393d03..d9d45837 100644
--- a/configure.ac
+++ b/configure.ac
@@ -23,12 +23,6 @@ AC_USE_SYSTEM_EXTENSIONS
 AC_SYS_LARGEFILE
 AC_PROG_CC
 AC_PROG_CC_STDC
-AC_PROG_LN_S
-AC_PROG_MAKE_SET
-AC_PROG_INSTALL
-AC_PROG_MKDIR_P
-
-pa_no_optimize=false
 
 dnl If the user did not specify a CFLAGS default, change default
 dnl to -O0 for debugging
@@ -36,6 +30,19 @@ PA_ARG_DISABLED([optimization],
  [compile without optimization (-O0) to help debugging],
  [pa_no_optimize=true])
 
+dnl LLVM doesn't error out on invalid -W options unless this option is
+dnl specified first.  Enable this so this script can actually discover
+dnl which -W options are possible for this compiler.
+PA_ADD_CFLAGS([-Werror=unknown-warning-option])
+
+dnl Other programs
+AC_PROG_LN_S
+AC_PROG_MAKE_SET
+AC_PROG_INSTALL
+AC_PROG_MKDIR_P
+
+pa_no_optimize=false
+
 dnl Compile and link with dwarf debug
 PA_ARG_ENABLED([gdb],
  [disable optimization and compile with extra debug information for GDB debugger],
@@ -282,6 +289,7 @@ PA_FUNC_ATTRIBUTE(format, [printf,1,2], int, [const char *, ...], ["%d",1])
 PA_FUNC_ATTRIBUTE(const)
 PA_FUNC_ATTRIBUTE(pure)
 PA_FUNC_ATTRIBUTE(cold,,,,,unlikely_func)
+PA_FUNC_ATTRIBUTE(unused)
 PA_FUNC_ATTRIBUTE_ERROR
 
 dnl
@@ -320,22 +328,25 @@ PA_ARG_ENABLED([sanitizer],
 
 dnl
 dnl Don't make symbols visible, there is no point and it just
-dnl makes the code slower.
+dnl makes the code slower. This mainly affects ELF.
 dnl
 PA_ADD_CFLAGS([-fvisibility=hidden])
 
-dnl If we have gcc, add appropriate code cleanliness options
+dnl
+dnl If we have gcc, add appropriate code cleanliness options.  Do this
+dnl here at the end, because configure relies on being able to use
+dnl some very, very old C constructs.
+dnl
 PA_ADD_CFLAGS([-Wall])
 PA_ARG_DISABLED([pedantic],
 [disable some extra paranoid compiler warnings],
 [],
 [PA_ADD_CFLAGS([-W])
  PA_ADD_CFLAGS([-pedantic])
- PA_ADD_CFLAGS([-Wc90-c99-compat])])
-dnl LLVM doesn't error out on invalid -W options unless this option is
-dnl specified first.  Enable this so this script can actually discover
-dnl which -W options are possible for this compiler.
-PA_ADD_CFLAGS([-Werror=unknown-warning-option])
+ PA_ADD_CFLAGS([-Wc90-c99-compat])
+ PA_ADD_CFLAGS([-Wc99-compat])
+ PA_ADD_CFLAGS([-Wc99-extensions])
+])
 dnl Suppress format warning on Windows targets due to their <inttypes.h>
 PA_ADD_CFLAGS([-Wpedantic-ms-format],[-Wno-pedantic-ms-format])
 PA_ADD_CFLAGS([-Wlong-long],[-Wno-long-long])
@@ -347,6 +358,7 @@ dnl on compilers with gcc-like command line syntax we pass the -fwrapv
 dnl option for exactly that reason.
 PA_ADD_CFLAGS([-Wshift-negative-value],[-Wno-shift-negative-value])
 
+dnl Want to turn this on at some point...
 dnl PA_ADD_CFLAGS([-Wwrite-strings])
 PA_ARG_ENABLED([werror],
  [compile with -Werror to error out on any warning],
diff --git a/include/compiler.h b/include/compiler.h
index 43984338..a1905d27 100644
--- a/include/compiler.h
+++ b/include/compiler.h
@@ -1,5 +1,5 @@
 /* ----------------------------------------------------------------------- *
- *   
+ *
  *   Copyright 2007-2018 The NASM Authors - All Rights Reserved
  *   See the file AUTHORS included with the NASM distribution for
  *   the specific copyright holders.
@@ -14,7 +14,7 @@
  *     copyright notice, this list of conditions and the following
  *     disclaimer in the documentation and/or other materials provided
  *     with the distribution.
- *     
+ *
  *     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
  *     CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
  *     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
@@ -310,6 +310,27 @@ static inline void *mempcpy(void *dst, const void *src, size_t n)
 #define printf_func(fmt, list)     format_func3(printf,fmt,list)
 #define printf_func_ptr(fmt, list) format_func3_ptr(printf,fmt,list)
 
+/*
+ * A static [inline] function which either is currently unused but
+ * likely to be used in the future, or used only under some #if
+ * combinations.  Mark with this option to suppress compiler
+ * warnings.
+ *
+ * This is better than #if(def) because it still lets the compiler
+ * analyze the function for validity, and it works even for the
+ * conditional use case.
+ *
+ * The macro UNUSED is set to 1 if the unused macro is meaningful,
+ * otherwise 0; this may be useful in some #if statements.
+ */
+#ifdef HAVE_FUNC_ATTRIBUTE_UNUSED
+# define unused __attribute__((unused))
+# define UNUSED 1
+#else
+# define unused
+# define UNUSED 0
+#endif
+
 /* Determine probabilistically if something is a compile-time constant */
 #ifdef HAVE___BUILTIN_CONSTANT_P
 # if defined(__GNUC__) && (__GNUC__ >= 5)
diff --git a/include/strlist.h b/include/strlist.h
index 2c80d0be..f1775abd 100644
--- a/include/strlist.h
+++ b/include/strlist.h
@@ -1,6 +1,6 @@
 /* ----------------------------------------------------------------------- *
  *
- *   Copyright 1996-2018 The NASM Authors - All Rights Reserved
+ *   Copyright 1996-2020 The NASM Authors - All Rights Reserved
  *   See the file AUTHORS included with the NASM distribution for
  *   the specific copyright holders.
  *
@@ -78,10 +78,10 @@ static inline size_t strlist_size(const struct strlist *list)
 }
 
 struct strlist safe_alloc *strlist_alloc(bool uniq);
-const struct strlist_entry * never_null strlist_add(struct strlist *list, const char *str);
-const struct strlist_entry * printf_func(2, 3) never_null
+const struct strlist_entry *strlist_add(struct strlist *list, const char *str);
+const struct strlist_entry * printf_func(2, 3)
 	strlist_printf(struct strlist *list, const char *fmt, ...);
-const struct strlist_entry * never_null
+const struct strlist_entry *
 	strlist_vprintf(struct strlist *list, const char *fmt, va_list ap);
 const struct strlist_entry *
 strlist_find(const struct strlist *list, const char *str);