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Date: Fri, 29 Mar 2024 16:08:10 -0700
From: "Paul E. McKenney" <paulmck@kernel.org>
To: kernel test robot <lkp@intel.com>
Cc: oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [paulmck-rcu:dev.2024.03.27b 61/69] lib/cmpxchg-emu.c:24:11:
 warning: no previous prototype for 'cmpxchg_emu_u8'
Message-ID: <e4b7ecac-719e-40f5-80b5-7a1c63e72b33@paulmck-laptop>
Reply-To: paulmck@kernel.org
References: <202403300508.Xz7XNp71-lkp@intel.com>
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In-Reply-To: <202403300508.Xz7XNp71-lkp@intel.com>

On Sat, Mar 30, 2024 at 05:26:12AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2024.03.27b
> head:   786fab3085d764055a78edb54023420920344333
> commit: b48ffed4c636b96d2be7a93806870772ce34961f [61/69] csky: Emulate one-byte and two-byte cmpxchg
> config: csky-allnoconfig (https://download.01.org/0day-ci/archive/20240330/202403300508.Xz7XNp71-lkp@intel.com/config)
> compiler: csky-linux-gcc (GCC) 13.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240330/202403300508.Xz7XNp71-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202403300508.Xz7XNp71-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> lib/cmpxchg-emu.c:24:11: warning: no previous prototype for 'cmpxchg_emu_u8' [-Wmissing-prototypes]
>       24 | uintptr_t cmpxchg_emu_u8(volatile u8 *p, uintptr_t old, uintptr_t new)
>          |           ^~~~~~~~~~~~~~
> >> lib/cmpxchg-emu.c:51:11: warning: no previous prototype for 'cmpxchg_emu_u16' [-Wmissing-prototypes]
>       51 | uintptr_t cmpxchg_emu_u16(volatile u16 *p, uintptr_t old, uintptr_t new)
>          |           ^~~~~~~~~~~~~~~

Again, good catch, and thank you for the testing!  Does the patch at the
end of this email fix things for you?

							Thanx, Paul

> vim +/cmpxchg_emu_u8 +24 lib/cmpxchg-emu.c
> 
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  22  
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  23  /* Emulate one-byte cmpxchg() in terms of 4-byte cmpxchg. */
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17 @24  uintptr_t cmpxchg_emu_u8(volatile u8 *p, uintptr_t old, uintptr_t new)
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  25  {
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  26  	u32 *p32 = (u32 *)(((uintptr_t)p) & ~0x3);
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  27  	int i = ((uintptr_t)p) & 0x3;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  28  	union u8_32 old32;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  29  	union u8_32 new32;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  30  	u32 ret;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  31  
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  32  	old32.w = READ_ONCE(*p32);
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  33  	do {
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  34  		if (old32.b[i] != old)
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  35  			return old32.b[i];
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  36  		new32.w = old32.w;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  37  		new32.b[i] = new;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  38  		instrument_atomic_read_write(p, 1);
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  39  		ret = data_race(cmpxchg(p32, old32.w, new32.w));
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  40  	} while (ret != old32.w);
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  41  	return old;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  42  }
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  43  EXPORT_SYMBOL_GPL(cmpxchg_emu_u8);
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  44  
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  45  union u16_32 {
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  46  	u16 h[2];
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  47  	u32 w;
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  48  };
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  49  
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17  50  /* Emulate two-byte cmpxchg() in terms of 4-byte cmpxchg. */
> 0bbce967f3ecfc Paul E. McKenney 2024-03-17 @51  uintptr_t cmpxchg_emu_u16(volatile u16 *p, uintptr_t old, uintptr_t new)
> 
> :::::: The code at line 24 was first introduced by commit
> :::::: 0bbce967f3ecfc6da1e7e8756b0d398e791b8dee lib: Add one-byte and two-byte cmpxchg() emulation functions
> 
> :::::: TO: Paul E. McKenney <paulmck@kernel.org>
> :::::: CC: Paul E. McKenney <paulmck@kernel.org>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki

commit a326496eb88936b291adea830c2e59e74ca1d373
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Fri Mar 29 16:06:45 2024 -0700

    squash! lib: Add one-byte and two-byte cmpxchg() emulation functions
    
    [ paulmck: Apply kernel test robot feedback. ]
    
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/lib/cmpxchg-emu.c b/lib/cmpxchg-emu.c
index abdd451767220..a88c4f3c88430 100644
--- a/lib/cmpxchg-emu.c
+++ b/lib/cmpxchg-emu.c
@@ -14,6 +14,7 @@
 #include <linux/panic.h>
 #include <linux/bug.h>
 #include <asm-generic/rwonce.h>
+#include <linux/cmpxchg-emu.h>
 
 union u8_32 {
 	u8 b[4];