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objtool: Fix gcov check for older versions of GCC

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Objtool tries to silence 'unreachable instruction' warnings when it
detects gcov is enabled, because gcov produces a lot of unreachable
instructions and they don't really matter.

However, the 0-day bot is still reporting some unreachable instruction
warnings with CONFIG_GCOV_KERNEL=y on GCC 4.6.4.

As it turns out, objtool's gcov detection doesn't work with older
versions of GCC because they don't create a bunch of symbols with the
'gcov.' prefix like newer versions of GCC do.

Move the gcov check out of objtool and instead just create a new
'--no-unreachable' flag which can be passed in by the kernel Makefile
when CONFIG_GCOV_KERNEL is defined.

Also rename the 'nofp' variable to 'no_fp' for consistency with the new
'no_unreachable' variable.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9cfffb1168 ("objtool: Skip all "unreachable instruction" warnings for gcov kernels")
Link: http://lkml.kernel.org/r/c243dc78eb2ffdabb6e927844dea39b6033cd395.1500939244.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Josh Poimboeuf 2017-07-24 18:34:14 -05:00 committed by Ingo Molnar
parent 9683a64fc3
commit 867ac9d737
5 changed files with 17 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
scripts/Makefile.build
View File

@ -262,6 +262,9 @@ objtool_args = check
ifndef CONFIG_FRAME_POINTER
objtool_args += --no-fp
endif
ifdef CONFIG_GCOV_KERNEL
objtool_args += --no-unreachable
endif
# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file

7
tools/objtool/builtin-check.c
View File

@ -29,7 +29,7 @@
#include "builtin.h"
#include "check.h"
bool nofp;
bool no_fp, no_unreachable;
static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@ -37,7 +37,8 @@ static const char * const check_usage[] = {
};
const struct option check_options[] = {
OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
OPT_BOOLEAN('f', "no-fp", &no_fp, "Skip frame pointer validation"),
OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"),
OPT_END(),
};
@ -52,5 +53,5 @@ int cmd_check(int argc, const char **argv)
objname = argv[0];
return check(objname, nofp, false);
return check(objname, no_fp, no_unreachable, false);
}

4
tools/objtool/builtin-orc.c
View File

@ -37,7 +37,7 @@ static const char *orc_usage[] = {
};
extern const struct option check_options[];
extern bool nofp;
extern bool no_fp, no_unreachable;
int cmd_orc(int argc, const char **argv)
{
@ -51,7 +51,7 @@ int cmd_orc(int argc, const char **argv)
objname = argv[0];
return check(objname, nofp, true);
return check(objname, no_fp, no_unreachable, true);
}

36
tools/objtool/check.c
View File

@ -33,7 +33,7 @@ struct alternative {
};
const char *objname;
static bool nofp;
static bool no_fp;
struct cfi_state initial_func_cfi;
struct instruction *find_insn(struct objtool_file *file,
@ -59,19 +59,6 @@ static struct instruction *next_insn_same_sec(struct objtool_file *file,
return next;
}
static bool gcov_enabled(struct objtool_file *file)
{
struct section *sec;
struct symbol *sym;
for_each_sec(file, sec)
list_for_each_entry(sym, &sec->symbol_list, list)
if (!strncmp(sym->name, "__gcov_.", 8))
return true;
return false;
}
#define func_for_each_insn(file, func, insn) \
for (insn = find_insn(file, func->sec, func->offset); \
insn && &insn->list != &file->insn_list && \
@ -1174,7 +1161,7 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
regs[CFI_BP].base = CFI_BP;
regs[CFI_BP].offset = -state->stack_size;
state->bp_scratch = false;
} else if (!nofp) {
} else if (!no_fp) {
WARN_FUNC("unknown stack-related register move",
insn->sec, insn->offset);
@ -1345,7 +1332,7 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
}
/* detect when asm code uses rbp as a scratch register */
if (!nofp && insn->func && op->src.reg == CFI_BP &&
if (!no_fp && insn->func && op->src.reg == CFI_BP &&
cfa->base != CFI_BP)
state->bp_scratch = true;
break;
@ -1593,7 +1580,7 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
/* fallthrough */
case INSN_CALL_DYNAMIC:
if (!nofp && func && !has_valid_stack_frame(&state)) {
if (!no_fp && func && !has_valid_stack_frame(&state)) {
WARN_FUNC("call without frame pointer save/setup",
sec, insn->offset);
return 1;
@ -1779,15 +1766,6 @@ static int validate_reachable_instructions(struct objtool_file *file)
if (insn->visited || ignore_unreachable_insn(insn))
continue;
/*
* gcov produces a lot of unreachable instructions. If we get
* an unreachable warning and the file has gcov enabled, just
* ignore it, and all other such warnings for the file. Do
* this here because this is an expensive function.
*/
if (gcov_enabled(file))
return 0;
WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
return 1;
}
@ -1812,13 +1790,13 @@ static void cleanup(struct objtool_file *file)
elf_close(file->elf);
}
int check(const char *_objname, bool _nofp, bool orc)
int check(const char *_objname, bool _no_fp, bool no_unreachable, bool orc)
{
struct objtool_file file;
int ret, warnings = 0;
objname = _objname;
nofp = _nofp;
no_fp = _no_fp;
file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
if (!file.elf)
@ -1829,7 +1807,7 @@ int check(const char *_objname, bool _nofp, bool orc)
file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
file.rodata = find_section_by_name(file.elf, ".rodata");
file.c_file = find_section_by_name(file.elf, ".comment");
file.ignore_unreachables = false;
file.ignore_unreachables = no_unreachable;
file.hints = false;
arch_initial_func_cfi_state(&initial_func_cfi);

2
tools/objtool/check.h
View File

@ -61,7 +61,7 @@ struct objtool_file {
bool ignore_unreachables, c_file, hints;
};
int check(const char *objname, bool nofp, bool orc);
int check(const char *objname, bool no_fp, bool no_unreachable, bool orc);
struct instruction *find_insn(struct objtool_file *file,
struct section *sec, unsigned long offset);