Re: [PATCH 1/2] compiler.h: Avoid using inline asm operand modifiers

From: Josh Poimboeuf
Date: Mon Nov 08 2021 - 11:50:27 EST


On Mon, Nov 08, 2021 at 04:40:38PM +0100, Vasily Gorbik wrote:
> > Does this work on s390?
> >
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index 3d5af56337bd..42935500a712 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -115,24 +115,18 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> > * The __COUNTER__ based labels are a hack to make each instance of the macros
> > * unique, to convince GCC not to merge duplicate inline asm statements.
> > */
> > -#define __stringify_label(n) #n
> > -
> > -#define __annotate_reachable(c) ({ \
> > - asm volatile(__stringify_label(c) ":\n\t" \
> > +#define annotate_reachable() ({ \
> > + asm volatile("%c0:\n\t" \
> > ".pushsection .discard.reachable\n\t" \
> > - ".long " __stringify_label(c) "b - .\n\t" \
> > - ".popsection\n\t"); \
> > + ".long %c0b - .\n\t" \
> > + ".popsection\n\t" : : "i" (__COUNTER__ & 0x7f)); \
> > })
>
> hm, could we just add asm input back and not use it? and keep
> __stringify_label(c) as is? would that work as well?

Yeah, that seems to work:

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 3d5af56337bd..429dcebe2b99 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -121,7 +121,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
asm volatile(__stringify_label(c) ":\n\t" \
".pushsection .discard.reachable\n\t" \
".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define annotate_reachable() __annotate_reachable(__COUNTER__)

@@ -129,7 +129,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
asm volatile(__stringify_label(c) ":\n\t" \
".pushsection .discard.unreachable\n\t" \
".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define annotate_unreachable() __annotate_unreachable(__COUNTER__)

diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h
index fa2cd8c63dcc..24359b4a9605 100644
--- a/include/linux/instrumentation.h
+++ b/include/linux/instrumentation.h
@@ -11,7 +11,7 @@
asm volatile(__stringify(c) ": nop\n\t" \
".pushsection .discard.instr_begin\n\t" \
".long " __stringify(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define instrumentation_begin() __instrumentation_begin(__COUNTER__)

@@ -50,7 +50,7 @@
asm volatile(__stringify(c) ": nop\n\t" \
".pushsection .discard.instr_end\n\t" \
".long " __stringify(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define instrumentation_end() __instrumentation_end(__COUNTER__)
#else