Commit 2058f6d1 authored by Josh Poimboeuf's avatar Josh Poimboeuf
Browse files

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: default avatarPetr Mladek <pmladek@suse.com>
Tested-by: default avatarJoe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
parent ebe864b5

tools/objtool/check.c

+45 −12
Original line number Diff line number Diff line
@@ -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;

	}

tools/objtool/elf.c

+0 −17
Original line number Diff line number Diff line
@@ -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)

tools/objtool/include/objtool/elf.h

+0 −2
Original line number Diff line number Diff line
@@ -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);