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Date: Tue, 8 May 2018 08:34:47 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: damian <damian.tometzki@...oud.com>, peterz@...radead.org,
linux-kernel@...r.kernel.org
Subject: Re: Kernel build with gcc 8 a lot of warnings
On Tue, May 08, 2018 at 07:51:26AM +0200, Greg KH wrote:
> On Sun, May 06, 2018 at 11:54:53PM -0500, Josh Poimboeuf wrote:
> > On Sat, May 05, 2018 at 09:21:12PM +0200, damian wrote:
> > > Helllo together,
> > >
> > > Hello everybody,
> > >
> > > is something special to note when kernel build with gcc 8? I receive various warnings from the objtool:
> > > With GCC 7 works all fine.
> > >
> > > kernel/cgroup/cgroup.o: warning: objtool: parse_cgroup_root_flags()+0x40: sibling call from callable instruction with modified stack frame
> > > kernel/cgroup/cgroup.o: warning: objtool: cgroup_addrm_files()+0x2a3: sibling call from callable instruction with modified stack frame
> > > kernel/cgroup/cgroup.o: warning: objtool: cgroup_apply_control_enable()+0x20b: sibling call from callable instruction with modified stack frame
> > > kernel/cgroup/cgroup.o: warning: objtool: rebind_subsystems()+0x296: sibling call from callable instruction with modified stack frame
> > > kernel/cgroup/cgroup.o: warning: objtool: cgroup_sk_alloc_disable()+0x10: sibling call from callable instruction with modified stack frame
> > > kernel/cgroup/cgroup.o: warning: objtool: parse_cgroup_root_flags.cold.45()+0xa: call without frame pointer save/setup
> > > kernel/cgroup/cgroup.o: warning: objtool: cgroup_addrm_files.cold.46()+0x17: call without frame pointer save/setup
> > > kernel/cgroup/cgroup.o: warning: objtool: cgroup_apply_control_enable.cold.47()+0x24: call without frame pointer save/setup
> > > kernel/cgroup/cgroup.o: warning: objtool: rebind_subsystems.cold.48()+0x10: call without frame pointer save/setup
> > > kernel/cgroup/cgroup.o: warning: objtool: cgroup_sk_alloc_disable.cold.49()+0x7: call without frame pointer save/setup
> > > CC kernel/cgroup/stat.o
> > > CC [M] arch/x86/kvm/../../../virt/kvm/kvm_main.o
> > > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_register_lapic()+0x10: sibling call from callable instruction with modified stack frame
> > > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_map_cpu()+0x2c: sibling call from callable instruction with modified stack frame
> > > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_register_lapic.cold.6()+0x7: call without frame pointer save/setup
> > > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_map_cpu.cold.7()+0x7: call without frame pointer save/setup
> >
> > Thanks, this is a known issue with GCC 8 that I haven't gotten a chance
> > to fix yet. They're related to the fact that GCC 8 is splitting out
> > 'unlikely' code into 'cold' subfunctions in .text.unlikely.
> >
> > I've got some old patches that fix it. Now that GCC 8 is out, I'll need
> > get the patches dusted off and cleaned up for merging.
>
> Any pointers to these patches? Archi linux just changed their default
> compiler to gcc 8 and now I'm seeing this in my local builds :(
I'm still dusting the code off, but this fixes most of the warnings.
The rest of the code should hopefully be ready soon.
From: Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [PATCH] objtool: Detect GCC 8 cold subfunctions
GCC 8 moves a lot of unlikely code out of line to "cold" subfunctions in
.text.unlikely. Properly detect the new subfunctions and treat them as
extensions of the original functions.
This fixes a bunch of warnings like:
kernel/cgroup/cgroup.o: warning: objtool: parse_cgroup_root_flags()+0x33: sibling call from callable instruction with modified stack frame
kernel/cgroup/cgroup.o: warning: objtool: cgroup_addrm_files()+0x290: sibling call from callable instruction with modified stack frame
kernel/cgroup/cgroup.o: warning: objtool: cgroup_apply_control_enable()+0x25b: sibling call from callable instruction with modified stack frame
kernel/cgroup/cgroup.o: warning: objtool: rebind_subsystems()+0x325: sibling call from callable instruction with modified stack frame
Reported-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
tools/objtool/check.c | 7 ++++---
tools/objtool/elf.c | 3 +++
tools/objtool/elf.h | 1 +
3 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 264522d4e4af..a8b3a8613b5e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1753,7 +1753,6 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
while (1) {
next_insn = next_insn_same_sec(file, insn);
-
if (file->c_file && func && insn->func && func != insn->func) {
WARN("%s() falls through to next function %s()",
func->name, insn->func->name);
@@ -1869,7 +1868,9 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
case INSN_JUMP_UNCONDITIONAL:
if (insn->jump_dest &&
(!func || !insn->jump_dest->func ||
- func == insn->jump_dest->func)) {
+ func == insn->jump_dest->func ||
+ insn->func->subfunc ||
+ insn->jump_dest->func->subfunc)) {
ret = validate_branch(file, insn->jump_dest,
state);
if (ret)
@@ -2064,7 +2065,7 @@ static int validate_functions(struct objtool_file *file)
for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
- if (func->type != STT_FUNC)
+ if (func->type != STT_FUNC || func->subfunc)
continue;
insn = find_insn(file, sec, func->offset);
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index c1c338661699..0c0c7ab4a014 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -260,6 +260,9 @@ static int read_symbols(struct elf *elf)
sym->offset = sym->sym.st_value;
sym->len = sym->sym.st_size;
+ if (sym->type == STT_FUNC && strstr(sym->name, ".cold."))
+ sym->subfunc = true;
+
/* sorted insert into a per-section list */
entry = &sym->sec->symbol_list;
list_for_each_prev(tmp, &sym->sec->symbol_list) {
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index d86e2ff14466..dc411f9859b1 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -61,6 +61,7 @@ struct symbol {
unsigned char bind, type;
unsigned long offset;
unsigned int len;
+ bool subfunc;
};
struct rela {
--
2.17.0
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