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objtool: Detect falling through to the next function 

There are several cases in compiled C code where a function may not
return at the end, and may instead fall through to the next function.

That may indicate a bug in the code, or a gcc bug, or even an objtool
bug.  But in each case, objtool reports an unhelpful warning, something
like:

  drivers/scsi/qla2xxx/qla_attr.o: warning: objtool: qla2x00_get_fc_host_stats()+0x0: duplicate frame pointer save
  drivers/scsi/qla2xxx/qla_attr.o: warning: objtool: qla2x00_get_fc_host_stats()+0x0: frame pointer state mismatch

Detect this situation and print a more useful error message:

  drivers/scsi/qla2xxx/qla_attr.o: warning: objtool: qla2x00_get_host_fabric_name() falls through to next function qla2x00_get_starget_node_name()

Also add some information about this warning and its potential causes to
the documentation.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/caa4ec6c687931db805e692d4e4bf06cd87d33e6.1460729697.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Josh Poimboeuf 2016-04-15 09:17:10 -05:00 committed by Ingo Molnar
parent 7e578441a4
commit b1547d3101
2 changed files with 61 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
tools/objtool/Documentation/stack-validation.txt
View File

@ -299,18 +299,38 @@ they mean, and suggestions for how to fix them.
Errors in .c files
------------------
If you're getting an objtool error in a compiled .c file, chances are
the file uses an asm() statement which has a "call" instruction. An
asm() statement with a call instruction must declare the use of the
stack pointer in its output operand. For example, on x86_64:
1. c_file.o: warning: objtool: funcA() falls through to next function funcB()
register void *__sp asm("rsp");
asm volatile("call func" : "+r" (__sp));
This means that funcA() doesn't end with a return instruction or an
unconditional jump, and that objtool has determined that the function
can fall through into the next function. There could be different
reasons for this:
Otherwise the stack frame may not get created before the call.
1) funcA()'s last instruction is a call to a "noreturn" function like
panic(). In this case the noreturn function needs to be added to
objtool's hard-coded global_noreturns array. Feel free to bug the
objtool maintainer, or you can submit a patch.
Another possible cause for errors in C code is if the Makefile removes
-fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
2) funcA() uses the unreachable() annotation in a section of code
that is actually reachable.
3) If funcA() calls an inline function, the object code for funcA()
might be corrupt due to a gcc bug. For more details, see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
2. If you're getting any other objtool error in a compiled .c file, it
may be because the file uses an asm() statement which has a "call"
instruction. An asm() statement with a call instruction must declare
the use of the stack pointer in its output operand. For example, on
x86_64:
register void *__sp asm("rsp");
asm volatile("call func" : "+r" (__sp));
Otherwise the stack frame may not get created before the call.
3. Another possible cause for errors in C code is if the Makefile removes
-fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
Also see the above section for .S file errors for more information what
the individual error messages mean.

46
tools/objtool/builtin-check.c
View File

@ -54,6 +54,7 @@ struct instruction {
struct symbol *call_dest;
struct instruction *jump_dest;
struct list_head alts;
struct symbol *func;
};
struct alternative {
@ -66,7 +67,7 @@ struct objtool_file {
struct list_head insn_list;
DECLARE_HASHTABLE(insn_hash, 16);
struct section *rodata, *whitelist;
bool ignore_unreachables;
bool ignore_unreachables, c_file;
};
const char *objname;
@ -229,7 +230,7 @@ static int __dead_end_function(struct objtool_file *file, struct symbol *func,
}
}
if (insn->type == INSN_JUMP_DYNAMIC)
if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
/* sibling call */
return 0;
}
@ -249,6 +250,7 @@ static int dead_end_function(struct objtool_file *file, struct symbol *func)
static int decode_instructions(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;
unsigned long offset;
struct instruction *insn;
int ret;
@ -282,6 +284,21 @@ static int decode_instructions(struct objtool_file *file)
hash_add(file->insn_hash, &insn->hash, insn->offset);
list_add_tail(&insn->list, &file->insn_list);
}
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
if (!find_insn(file, sec, func->offset)) {
WARN("%s(): can't find starting instruction",
func->name);
return -1;
}
func_for_each_insn(file, func, insn)
if (!insn->func)
insn->func = func;
}
}
return 0;
@ -824,6 +841,7 @@ static int validate_branch(struct objtool_file *file,
struct alternative *alt;
struct instruction *insn;
struct section *sec;
struct symbol *func = NULL;
unsigned char state;
int ret;
@ -838,6 +856,16 @@ static int validate_branch(struct objtool_file *file,
}
while (1) {
if (file->c_file && insn->func) {
if (func && func != insn->func) {
WARN("%s() falls through to next function %s()",
func->name, insn->func->name);
return 1;
}
func = insn->func;
}
if (insn->visited) {
if (frame_state(insn->state) != frame_state(state)) {
WARN_FUNC("frame pointer state mismatch",
@ -848,13 +876,6 @@ static int validate_branch(struct objtool_file *file,
return 0;
}
/*
* Catch a rare case where a noreturn function falls through to
* the next function.
*/
if (is_fentry_call(insn) && (state & STATE_FENTRY))
return 0;
insn->visited = true;
insn->state = state;
@ -1060,12 +1081,8 @@ static int validate_functions(struct objtool_file *file)
continue;
insn = find_insn(file, sec, func->offset);
if (!insn) {
WARN("%s(): can't find starting instruction",
func->name);
warnings++;
if (!insn)
continue;
}
ret = validate_branch(file, insn, 0);
warnings += ret;
@ -1162,6 +1179,7 @@ int cmd_check(int argc, const char **argv)
file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
file.rodata = find_section_by_name(file.elf, ".rodata");
file.ignore_unreachables = false;
file.c_file = find_section_by_name(file.elf, ".comment");
ret = decode_sections(&file);
if (ret < 0)