objtool: Refactor prefix symbol creation code

The prefix symbol creation code currently ignores all errors, presumably
because some functions don't have the leading NOPs.

Shuffle the code around a bit, improve the error handling and document
why some errors are ignored.

Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8d17d930d0c8c092ab1c00747f6f88041551f838..b2659fbf7bc955b522b30a28b226519eaede9176 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -15,6 +15,7 @@
 #include <objtool/special.h>
 #include <objtool/warn.h>
 #include <objtool/checksum.h>
+#include <objtool/util.h>
 
 #include <linux/objtool_types.h>
 #include <linux/hashtable.h>
@@ -4233,14 +4234,43 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
        return false;
 }
 
-static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
+/*
+ * For FineIBT or kCFI, a certain number of bytes preceding the function may be
+ * NOPs.  Those NOPs may be rewritten at runtime and executed, so give them a
+ * proper function name: __pfx_<func>.
+ *
+ * The NOPs may not exist for the following cases:
+ *
+ *   - compiler cloned functions (*.cold, *.part0, etc)
+ *   - asm functions created with inline asm or without SYM_FUNC_START()
+ *
+ * So return 0 if the NOPs are missing or the function already has a prefix
+ * symbol.
+ */
+static int create_prefix_symbol(struct objtool_file *file, struct symbol *func)
 {
        struct instruction *insn, *prev;
+       char name[SYM_NAME_LEN];
        struct cfi_state *cfi;
 
+       if (!is_func_sym(func) || is_prefix_func(func) ||
+           func->cold || func->static_call_tramp)
+               return 0;
+
+       if ((strlen(func->name) + sizeof("__pfx_") > SYM_NAME_LEN)) {
+               WARN("%s: symbol name too long, can't create __pfx_ symbol",
+                     func->name);
+               return 0;
+       }
+
+       if (snprintf_check(name, SYM_NAME_LEN, "__pfx_%s", func->name))
+               return -1;
+
        insn = find_insn(file, func->sec, func->offset);
-       if (!insn)
+       if (!insn) {
+               WARN("%s: can't find starting instruction", func->name);
                return -1;
+       }
 
        for (prev = prev_insn_same_sec(file, insn);
             prev;
@@ -4248,22 +4278,27 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
                u64 offset;
 
                if (prev->type != INSN_NOP)
-                       return -1;
+                       return 0;
 
                offset = func->offset - prev->offset;
 
                if (offset > opts.prefix)
-                       return -1;
+                       return 0;
 
                if (offset < opts.prefix)
                        continue;
 
-               elf_create_prefix_symbol(file->elf, func, opts.prefix);
+               if (!elf_create_symbol(file->elf, name, func->sec,
+                                      GELF_ST_BIND(func->sym.st_info),
+                                      GELF_ST_TYPE(func->sym.st_info),
+                                      prev->offset, opts.prefix))
+                       return -1;
+
                break;
        }
 
        if (!prev)
-               return -1;
+               return 0;
 
        if (!insn->cfi) {
                /*
@@ -4281,7 +4316,7 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
        return 0;
 }
 
-static int add_prefix_symbols(struct objtool_file *file)
+static int create_prefix_symbols(struct objtool_file *file)
 {
        struct section *sec;
        struct symbol *func;
@@ -4291,10 +4326,8 @@ static int add_prefix_symbols(struct objtool_file *file)
                        continue;
 
                sec_for_each_sym(sec, func) {
-                       if (!is_func_sym(func))
-                               continue;
-
-                       add_prefix_symbol(file, func);
+                       if (create_prefix_symbol(file, func))
+                               return -1;
                }
        }
 
@@ -4921,7 +4954,7 @@ int check(struct objtool_file *file)
        }
 
        if (opts.prefix) {
-               ret = add_prefix_symbols(file);
+               ret = create_prefix_symbols(file);
                if (ret)
                        goto out;
        }

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index e1daae0630be9851b6fc0ff7f1286271a456b6ac..4bb7ce994b6a76ef5ea6dc62345be70441cdcbb4 100644 (file)
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -942,23 +942,6 @@ struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec)
        return sym;
 }
 
-struct symbol *
-elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, size_t size)
-{
-       size_t namelen = strlen(orig->name) + sizeof("__pfx_");
-       char name[SYM_NAME_LEN];
-       unsigned long offset;
-
-       snprintf(name, namelen, "__pfx_%s", orig->name);
-
-       offset = orig->sym.st_value - size;
-
-       return elf_create_symbol(elf, name, orig->sec,
-                                GELF_ST_BIND(orig->sym.st_info),
-                                GELF_ST_TYPE(orig->sym.st_info),
-                                offset, size);
-}
-
 struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
                             unsigned int reloc_idx, unsigned long offset,
                             struct symbol *sym, s64 addend, unsigned int type)

diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index e2cd817fca5221241892b83321b169a3020df9fd..60f844e43c5a2602e85fb67ba7277158d24df9ad 100644 (file)
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -148,8 +148,6 @@ struct symbol *elf_create_symbol(struct elf *elf, const char *name,
                                 unsigned int type, unsigned long offset,
                                 size_t size);
 struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec);
-struct symbol *elf_create_prefix_symbol(struct elf *elf, struct symbol *orig,
-                                       size_t size);
 
 void *elf_add_data(struct elf *elf, struct section *sec, const void *data,
                   size_t size);