Re: [patch V6 00/37] x86/entry: Rework leftovers and merge plan

[Peter Zijlstra]

On Mon, May 18, 2020 at 10:24:53PM +0200, Thomas Gleixner wrote:
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
> > So on top of you entry-v8-full; I had to chase one of those
> > instrumentation_end() escapes an (extended) basic block chase (again!).
> >
> > --- a/arch/x86/include/asm/bug.h
> > +++ b/arch/x86/include/asm/bug.h
> > @@ -79,8 +79,8 @@ do {								\
> >  do {								\
> >  	instrumentation_begin();				\
> >  	_BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags));		\
> > -	instrumentation_end();					\
> >  	annotate_reachable();					\
> > +	instrumentation_end();					\
> >  } while (0)
> 
> I just applied this part and rebuilt:
> 
>  vmlinux.o: warning: objtool: rcu_eqs_enter.constprop.77()+0xa9: call to
>  rcu_preempt_deferred_qs() leaves .noinstr.text section
> 
> Did it go away after you disabled DEBUG_ENTRY perhaps?

Hehe, then all complaints would be gone :-)

So tglx/entry-v8-full + below patch:

$ make O=defconfig-build clean
...
$ make CC=gcc-9 O=defconfig-build/ vmlinux -j40 -s
vmlinux.o: warning: objtool: exc_debug()+0x158: call to trace_hwlat_timestamp() leaves .noinstr.text section
vmlinux.o: warning: objtool: exc_nmi()+0x190: call to trace_hwlat_timestamp() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_machine_check()+0x46: call to mce_rdmsrl() leaves .noinstr.text section
$

(it really isn't defconfig, but your config-fail + DEBUG_ENTRY)

---
 arch/x86/include/asm/bug.h |  2 +-
 include/linux/compiler.h   | 11 ++++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index f128e5c2ed42..fb34ff641e0a 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -79,8 +79,8 @@ do {								\
 do {								\
 	instrumentation_begin();				\
 	_BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags));		\
-	instrumentation_end();					\
 	annotate_reachable();					\
+	instrumentation_end();					\
 } while (0)
 
 #include <asm-generic/bug.h>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 7db5902f8f6e..f6f54e8e0797 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -120,25 +120,30 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 /* Annotate a C jump table to allow objtool to follow the code flow */
 #define __annotate_jump_table __section(.rodata..c_jump_table)
 
+#ifdef CONFIG_DEBUG_ENTRY
 /* Begin/end of an instrumentation safe region */
-#define instrumentation_begin() ({						\
+#define instrumentation_begin() ({					\
 	asm volatile("%c0:\n\t"						\
 		     ".pushsection .discard.instr_begin\n\t"		\
 		     ".long %c0b - .\n\t"				\
 		     ".popsection\n\t" : : "i" (__COUNTER__));		\
 })
 
-#define instrumentation_end() ({							\
-	asm volatile("%c0:\n\t"						\
+#define instrumentation_end() ({					\
+	asm volatile("%c0: nop\n\t"					\
 		     ".pushsection .discard.instr_end\n\t"		\
 		     ".long %c0b - .\n\t"				\
 		     ".popsection\n\t" : : "i" (__COUNTER__));		\
 })
+#endif /* CONFIG_DEBUG_ENTRY */
 
 #else
 #define annotate_reachable()
 #define annotate_unreachable()
 #define __annotate_jump_table
+#endif
+
+#ifndef instrumentation_begin
 #define instrumentation_begin()		do { } while(0)
 #define instrumentation_end()		do { } while(0)
 #endif