On Thu, 21 May 2020, Randy Dunlap wrote:
> On 5/21/20 7:12 AM, Stephen Rothwell wrote:
> > Hi all,
> >
> > Changes since 20200519:
> >
These are indeed caused by -flive-patching
> on x86_64:
>
> fs/open.o: warning: objtool: chmod_common()+0x104: unreachable instruction
> fs/namei.o: warning: objtool: do_renameat2()+0x482: unreachable instruction
Two "funny" ones. When CONFIG_FILE_LOCKING is not set, break_deleg_wait()
is just BUG(). GCC decides to isra optimize it to break_deleg_wait.isra.0
and call it in chmod_common() and do_renameat2() instead of just inline
it.
chmod_common() with -flive-patching:
981: e8 f7 fe ff ff callq 87d <break_deleg_wait.isra.0>
986: 41 89 c4 mov %eax,%r12d
989: 85 c0 test %eax,%eax
98b: 0f 84 76 ff ff ff je 907 <chmod_common+0x7b>
991: 48 89 df mov %rbx,%rdi
994: e8 00 00 00 00 callq 999 <chmod_common+0x10d>
995: R_X86_64_PLT32 __tsan_read8-0x4
without:
985: e8 f3 fe ff ff callq 87d <break_deleg_wait.isra.0>
98a: 48 89 df mov %rbx,%rdi
98d: e8 00 00 00 00 callq 992 <chmod_common+0x106>
98e: R_X86_64_PLT32 __tsan_read8-0x4
The error checking of break_deleg_wait() is correctly compiled out,
because it is unreachable.
I wondered how come objtool (correctly) says the instructions are
unreachable. It means it knows that break_deleg_wait.isra.0 is a dead end
(dead_end_function() returns true while checking INSN_CALL). And of course
"return 0;" in break_deleg_wait() is compiled out.
000000000000087d <break_deleg_wait.isra.0>:
87d: 55 push %rbp
87e: 48 89 e5 mov %rsp,%rbp
881: 48 8b 7d 08 mov 0x8(%rbp),%rdi
885: e8 00 00 00 00 callq 88a <break_deleg_wait.isra.0+0xd>
886: R_X86_64_PLT32 __tsan_func_entry-0x4
88a: 0f 0b ud2
One way to fix it is to mark break_deleg_wait() as __always_inline. Then
it all works.
Note: there are more functions calling break_deleg_wait() with this
pattern.
I'll try to find out which optimization does this, because it is a
slightly different scenario than hiding __noreturn from the callees.
Probably -fno-ipa-pure-const again.
> kernel/exit.o: warning: objtool: __ia32_sys_exit_group()+0x2e: unreachable instruction
Easy one. do_group_exit() is noreturn and should be marked as such.
> Full randconfig file is attached.
>
>
> --
> ~Randy
> Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Thanks for reporting, Randy.
Miroslav
---
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ac8bd95b5fe8..2b79932e924d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2546,7 +2546,7 @@ static inline int try_break_deleg(struct inode *inode, struct inode **delegated_
return 0;
}
-static inline int break_deleg_wait(struct inode **delegated_inode)
+static __always_inline int break_deleg_wait(struct inode **delegated_inode)
{
BUG();
return 0;
diff --git a/kernel/exit.c b/kernel/exit.c
index ed56917d50e3..9437c1ca37c5 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -876,7 +876,7 @@ SYSCALL_DEFINE1(exit, int, error_code)
* Take down every thread in the group. This is called by fatal signals
* as well as by sys_exit_group (below).
*/
-void
+void __noreturn
do_group_exit(int exit_code)
{
struct signal_struct *sig = current->signal;
