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

From: Peter Zijlstra
Date: Tue May 19 2020 - 04:39:03 EST


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