genksyms: track symbol checksum changes

Sometimes it is preferable to avoid changes of exported symbol checksums
(to avoid breaking externally provided modules).  When a checksum change
occurs, it can be hard to figure out what caused this change: underlying
types may have changed, or additional type information may simply have
become available at the point where a symbol is exported.

Add a new --reference option to genksyms which allows it to report why
checksums change, based on the type information dumps it creates with the
--dump-types flag.  Genksyms will read in such a dump from a previous run,
and report which symbols have changed (and why).

The behavior can be controlled for an entire build as follows: If
KBUILD_SYMTYPES is set, genksyms uses --dump-types to produce *.symtypes
dump files.  If any *.symref files exist, those will be used as the
reference to check against.  If KBUILD_PRESERVE is set, checksum changes
will fail the build.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

3 files changed, 239 insertions, 19 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 468fbc9016c7..d21f0eac2e52 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -153,12 +153,18 @@ $(obj)/%.i: $(src)/%.c FORCE
 
 quiet_cmd_cc_symtypes_c = SYM $(quiet_modtag) $@
 cmd_cc_symtypes_c          = \
+                set -e;                                                 \
                 $(CPP) -D__GENKSYMS__ $(c_flags) $<                     \
-                | $(GENKSYMS) -T $@ >/dev/null;                         \
+                | $(GENKSYMS) -T $@                                     \
+                              -r $(firstword $(wildcard                 \
+                                     $(@:.symtypes=.symref) /dev/null)) \
+                              $(if $(KBUILD_PRESERVE),-p)               \
+                              -a $(ARCH)                                \
+                  >/dev/null;                                           \
                 test -s $@ || rm -f $@
 
 $(obj)/%.symtypes : $(src)/%.c FORCE
-        $(call if_changed_dep,cc_symtypes_c)
+        $(call cmd,cc_symtypes_c)
 
 # C (.c) files
 # The C file is compiled and updated dependency information is generated.
@@ -187,7 +193,11 @@ cmd_modversions =							\
         if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then     \
                 $(CPP) -D__GENKSYMS__ $(c_flags) $<                     \
                 | $(GENKSYMS) $(if $(KBUILD_SYMTYPES),                  \
-                              -T $(@D)/$(@F:.o=.symtypes)) -a $(ARCH)   \
+                                   -T $(@:.o=.symtypes))                \
+                              -r $(firstword $(wildcard                 \
+                                     $(@:.o=.symref) /dev/null))        \
+                              $(if $(KBUILD_PRESERVE),-p)               \
+                              -a $(ARCH)                                \
                 > $(@D)/.tmp_$(@F:.o=.ver);                             \
                                                                         \
                 $(LD) $(LDFLAGS) -r -o $@ $(@D)/.tmp_$(@F)              \
diff --git a/scripts/genksyms/genksyms.c b/scripts/genksyms/genksyms.c
index c249274e005a..ddac1746908e 100644
--- a/scripts/genksyms/genksyms.c
+++ b/scripts/genksyms/genksyms.c
@@ -42,7 +42,8 @@ static FILE *debugfile;
 int cur_line = 1;
 char *cur_filename;
 
-static int flag_debug, flag_dump_defs, flag_dump_types, flag_warnings;
+static int flag_debug, flag_dump_defs, flag_reference, flag_dump_types,
+           flag_preserve, flag_warnings;
 static const char *arch = "";
 static const char *mod_prefix = "";
 
@@ -58,6 +59,8 @@ static const char *const symbol_type_name[] = {
 
 static int equal_list(struct string_list *a, struct string_list *b);
 static void print_list(FILE * f, struct string_list *list);
+static void print_location(void);
+static void print_type_name(enum symbol_type type, const char *name);
 
 /*----------------------------------------------------------------------*/
 
@@ -151,27 +154,68 @@ struct symbol *find_symbol(const char *name, enum symbol_type ns)
 
         for (sym = symtab[h]; sym; sym = sym->hash_next)
                 if (map_to_ns(sym->type) == map_to_ns(ns) &&
-                    strcmp(name, sym->name) == 0)
+                    strcmp(name, sym->name) == 0 &&
+                    sym->is_declared)
                         break;
 
         return sym;
 }
 
-struct symbol *add_symbol(const char *name, enum symbol_type type,
-                          struct string_list *defn, int is_extern)
+static int is_unknown_symbol(struct symbol *sym)
+{
+        struct string_list *defn;
+
+        return ((sym->type == SYM_STRUCT ||
+                 sym->type == SYM_UNION ||
+                 sym->type == SYM_ENUM) &&
+                (defn = sym->defn)  && defn->tag == SYM_NORMAL &&
+                        strcmp(defn->string, "}") == 0 &&
+                (defn = defn->next) && defn->tag == SYM_NORMAL &&
+                        strcmp(defn->string, "UNKNOWN") == 0 &&
+                (defn = defn->next) && defn->tag == SYM_NORMAL &&
+                        strcmp(defn->string, "{") == 0);
+}
+
+struct symbol *__add_symbol(const char *name, enum symbol_type type,
+                            struct string_list *defn, int is_extern,
+                            int is_reference)
 {
         unsigned long h = crc32(name) % HASH_BUCKETS;
         struct symbol *sym;
+        enum symbol_status status = STATUS_UNCHANGED;
 
         for (sym = symtab[h]; sym; sym = sym->hash_next) {
-                if (map_to_ns(sym->type) == map_to_ns(type)
-                    && strcmp(name, sym->name) == 0) {
-                        if (!equal_list(sym->defn, defn))
+                if (map_to_ns(sym->type) == map_to_ns(type) &&
+                    strcmp(name, sym->name) == 0) {
+                        if (is_reference)
+                                /* fall through */ ;
+                        else if (sym->type == type &&
+                                 equal_list(sym->defn, defn)) {
+                                sym->is_declared = 1;
+                                return sym;
+                        } else if (!sym->is_declared) {
+                                status = is_unknown_symbol(sym) ?
+                                        STATUS_DEFINED : STATUS_MODIFIED;
+                        } else {
                                 error_with_pos("redefinition of %s", name);
-                        return sym;
+                                return sym;
+                        }
+                        break;
                 }
         }
 
+        if (sym) {
+                struct symbol **psym;
+
+                for (psym = &symtab[h]; *psym; psym = &(*psym)->hash_next) {
+                        if (*psym == sym) {
+                                *psym = sym->hash_next;
+                                break;
+                        }
+                }
+                --nsyms;
+        }
+
         sym = xmalloc(sizeof(*sym));
         sym->name = name;
         sym->type = type;
@@ -183,6 +227,9 @@ struct symbol *add_symbol(const char *name, enum symbol_type type,
         sym->hash_next = symtab[h];
         symtab[h] = sym;
 
+        sym->is_declared = !is_reference;
+        sym->status = status;
+
         if (flag_debug) {
                 fprintf(debugfile, "Defn for %s %s == <",
                         symbol_type_name[type], name);
@@ -196,6 +243,18 @@ struct symbol *add_symbol(const char *name, enum symbol_type type,
         return sym;
 }
 
+struct symbol *add_symbol(const char *name, enum symbol_type type,
+                          struct string_list *defn, int is_extern)
+{
+        return __add_symbol(name, type, defn, is_extern, 0);
+}
+
+struct symbol *add_reference_symbol(const char *name, enum symbol_type type,
+                                    struct string_list *defn, int is_extern)
+{
+        return __add_symbol(name, type, defn, is_extern, 1);
+}
+
 /*----------------------------------------------------------------------*/
 
 void free_node(struct string_list *node)
@@ -236,6 +295,82 @@ static int equal_list(struct string_list *a, struct string_list *b)
         return !a && !b;
 }
 
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+
+struct string_list *read_node(FILE *f)
+{
+        char buffer[256];
+        struct string_list node = {
+                .string = buffer,
+                .tag = SYM_NORMAL };
+        int c;
+
+        while ((c = fgetc(f)) != EOF) {
+                if (c == ' ') {
+                        if (node.string == buffer)
+                                continue;
+                        break;
+                } else if (c == '\n') {
+                        if (node.string == buffer)
+                                return NULL;
+                        ungetc(c, f);
+                        break;
+                }
+                if (node.string >= buffer + sizeof(buffer) - 1) {
+                        fprintf(stderr, "Token too long\n");
+                        exit(1);
+                }
+                *node.string++ = c;
+        }
+        if (node.string == buffer)
+                return NULL;
+        *node.string = 0;
+        node.string = buffer;
+
+        if (node.string[1] == '#') {
+                int n;
+
+                for (n = 0; n < ARRAY_SIZE(symbol_type_name); n++) {
+                        if (node.string[0] == symbol_type_name[n][0]) {
+                                node.tag = n;
+                                node.string += 2;
+                                return copy_node(&node);
+                        }
+                }
+                fprintf(stderr, "Unknown type %c\n", node.string[0]);
+                exit(1);
+        }
+        return copy_node(&node);
+}
+
+static void read_reference(FILE *f)
+{
+        while (!feof(f)) {
+                struct string_list *defn = NULL;
+                struct string_list *sym, *def;
+                int is_extern = 0;
+
+                sym = read_node(f);
+                if (!sym)
+                        continue;
+                def = read_node(f);
+                if (def && def->tag == SYM_NORMAL &&
+                    !strcmp(def->string, "extern")) {
+                        is_extern = 1;
+                        free_node(def);
+                        def = read_node(f);
+                }
+                while (def) {
+                        def->next = defn;
+                        defn = def;
+                        def = read_node(f);
+                }
+                add_reference_symbol(xstrdup(sym->string), sym->tag,
+                                              defn, is_extern);
+                free_node(sym);
+        }
+}
+
 static void print_node(FILE * f, struct string_list *list)
 {
         if (list->tag != SYM_NORMAL) {
@@ -311,6 +446,7 @@ static unsigned long expand_and_crc_sym(struct symbol *sym, unsigned long crc)
 
                 case SYM_TYPEDEF:
                         subsym = find_symbol(cur->string, cur->tag);
+                        /* FIXME: Bad reference files can segfault here. */
                         if (subsym->expansion_trail) {
                                 if (flag_dump_defs)
                                         fprintf(debugfile, "%s ", cur->string);
@@ -347,9 +483,22 @@ static unsigned long expand_and_crc_sym(struct symbol *sym, unsigned long crc)
                                 t = n;
 
                                 n = xmalloc(sizeof(*n));
-                                n->string = xstrdup("{ UNKNOWN }");
+                                n->string = xstrdup("{");
                                 n->tag = SYM_NORMAL;
                                 n->next = t;
+                                t = n;
+
+                                n = xmalloc(sizeof(*n));
+                                n->string = xstrdup("UNKNOWN");
+                                n->tag = SYM_NORMAL;
+                                n->next = t;
+                                t = n;
+
+                                n = xmalloc(sizeof(*n));
+                                n->string = xstrdup("}");
+                                n->tag = SYM_NORMAL;
+                                n->next = t;
+                                t = n;
 
                                 subsym =
                                     add_symbol(cur->string, cur->tag, n, 0);
@@ -397,20 +546,42 @@ void export_symbol(const char *name)
                 error_with_pos("export undefined symbol %s", name);
         else {
                 unsigned long crc;
+                int has_changed = 0;
 
                 if (flag_dump_defs)
                         fprintf(debugfile, "Export %s == <", name);
 
                 expansion_trail = (struct symbol *)-1L;
 
+                sym->expansion_trail = expansion_trail;
+                expansion_trail = sym;
                 crc = expand_and_crc_sym(sym, 0xffffffff) ^ 0xffffffff;
 
                 sym = expansion_trail;
                 while (sym != (struct symbol *)-1L) {
                         struct symbol *n = sym->expansion_trail;
+
+                        if (sym->status != STATUS_UNCHANGED) {
+                                if (!has_changed) {
+                                        print_location();
+                                        fprintf(stderr, "%s: %s: modversion "
+                                                "changed because of changes "
+                                                "in ", flag_preserve ? "error" :
+                                                       "warning", name);
+                                } else
+                                        fprintf(stderr, ", ");
+                                print_type_name(sym->type, sym->name);
+                                if (sym->status == STATUS_DEFINED)
+                                        fprintf(stderr, " (became defined)");
+                                has_changed = 1;
+                                if (flag_preserve)
+                                        errors++;
+                        }
                         sym->expansion_trail = 0;
                         sym = n;
                 }
+                if (has_changed)
+                        fprintf(stderr, "\n");
 
                 if (flag_dump_defs)
                         fputs(">\n", debugfile);
@@ -421,13 +592,26 @@ void export_symbol(const char *name)
 }
 
 /*----------------------------------------------------------------------*/
+
+static void print_location(void)
+{
+        fprintf(stderr, "%s:%d: ", cur_filename ? : "<stdin>", cur_line);
+}
+
+static void print_type_name(enum symbol_type type, const char *name)
+{
+        if (type != SYM_NORMAL)
+                fprintf(stderr, "%s %s", symbol_type_name[type], name);
+        else
+                fprintf(stderr, "%s", name);
+}
+
 void error_with_pos(const char *fmt, ...)
 {
         va_list args;
 
         if (flag_warnings) {
-                fprintf(stderr, "%s:%d: ", cur_filename ? : "<stdin>",
-                        cur_line);
+                print_location();
 
                 va_start(args, fmt);
                 vfprintf(stderr, fmt, args);
@@ -445,7 +629,9 @@ static void genksyms_usage(void)
               "  -a, --arch            Select architecture\n"
               "  -d, --debug           Increment the debug level (repeatable)\n"
               "  -D, --dump            Dump expanded symbol defs (for debugging only)\n"
-              "  -T, --dump-types file Dump expanded types into file (for debugging only)\n"
+              "  -r, --reference file  Read reference symbols from a file\n"
+              "  -T, --dump-types file Dump expanded types into file\n"
+              "  -p, --preserve        Preserve reference modversions or fail\n"
               "  -w, --warnings        Enable warnings\n"
               "  -q, --quiet           Disable warnings (default)\n"
               "  -h, --help            Print this message\n"
@@ -454,7 +640,9 @@ static void genksyms_usage(void)
               "  -a                    Select architecture\n"
               "  -d                    Increment the debug level (repeatable)\n"
               "  -D                    Dump expanded symbol defs (for debugging only)\n"
-              "  -T file               Dump expanded types into file (for debugging only)\n"
+              "  -r file               Read reference symbols from a file\n"
+              "  -T file               Dump expanded types into file\n"
+              "  -p                    Preserve reference modversions or fail\n"
               "  -w                    Enable warnings\n"
               "  -q                    Disable warnings (default)\n"
               "  -h                    Print this message\n"
@@ -465,7 +653,7 @@ static void genksyms_usage(void)
 
 int main(int argc, char **argv)
 {
-        FILE *dumpfile = NULL;
+        FILE *dumpfile = NULL, *ref_file = NULL;
         int o;
 
 #ifdef __GNU_LIBRARY__
@@ -475,16 +663,18 @@ int main(int argc, char **argv)
                 {"warnings", 0, 0, 'w'},
                 {"quiet", 0, 0, 'q'},
                 {"dump", 0, 0, 'D'},
+                {"reference", 1, 0, 'r'},
                 {"dump-types", 1, 0, 'T'},
+                {"preserve", 0, 0, 'p'},
                 {"version", 0, 0, 'V'},
                 {"help", 0, 0, 'h'},
                 {0, 0, 0, 0}
         };
 
-        while ((o = getopt_long(argc, argv, "a:dwqVDT:h",
+        while ((o = getopt_long(argc, argv, "a:dwqVDr:T:ph",
                                 &long_opts[0], NULL)) != EOF)
 #else                           /* __GNU_LIBRARY__ */
-        while ((o = getopt(argc, argv, "a:dwqVDT:h")) != EOF)
+        while ((o = getopt(argc, argv, "a:dwqVDr:T:ph")) != EOF)
 #endif                          /* __GNU_LIBRARY__ */
                 switch (o) {
                 case 'a':
@@ -505,6 +695,14 @@ int main(int argc, char **argv)
                 case 'D':
                         flag_dump_defs = 1;
                         break;
+                case 'r':
+                        flag_reference = 1;
+                        ref_file = fopen(optarg, "r");
+                        if (!ref_file) {
+                                perror(optarg);
+                                return 1;
+                        }
+                        break;
                 case 'T':
                         flag_dump_types = 1;
                         dumpfile = fopen(optarg, "w");
@@ -513,6 +711,9 @@ int main(int argc, char **argv)
                                 return 1;
                         }
                         break;
+                case 'p':
+                        flag_preserve = 1;
+                        break;
                 case 'h':
                         genksyms_usage();
                         return 0;
@@ -533,6 +734,9 @@ int main(int argc, char **argv)
                 /* setlinebuf(debugfile); */
         }
 
+        if (flag_reference)
+                read_reference(ref_file);
+
         yyparse();
 
         if (flag_dump_types && visited_symbols) {
diff --git a/scripts/genksyms/genksyms.h b/scripts/genksyms/genksyms.h
index 2668287aa498..2831158426cd 100644
--- a/scripts/genksyms/genksyms.h
+++ b/scripts/genksyms/genksyms.h
@@ -29,6 +29,10 @@ enum symbol_type {
         SYM_NORMAL, SYM_TYPEDEF, SYM_ENUM, SYM_STRUCT, SYM_UNION
 };
 
+enum symbol_status {
+        STATUS_UNCHANGED, STATUS_DEFINED, STATUS_MODIFIED
+};
+
 struct string_list {
         struct string_list *next;
         enum symbol_type tag;
@@ -43,6 +47,8 @@ struct symbol {
         struct symbol *expansion_trail;
         struct symbol *visited;
         int is_extern;
+        int is_declared;
+        enum symbol_status status;
 };
 
 typedef struct string_list **yystype;