Hi,
This fixes ARC port to support configs lacking llock/scond using kernel assisted cmpxchg.
Thx, -Vineet
Vineet Gupta (3): NPTL/ARC: implement __arch_exchange_32_acq using native EX ARC: introduce explicit support for atomics NPTL/ARC: provide a kernel assisted atomic cmpxchg
extra/Configs/Config.arc | 8 +++++ libc/sysdeps/linux/arc/bits/atomic.h | 61 ++++++++++++++++++++++++++++++++++-- 2 files changed, 67 insertions(+), 2 deletions(-)
ARC EX instruction maps directly to this primitive, thus helps elide the llock/scond based retry loop where possible.
Signed-off-by: Vineet Gupta vgupta@synopsys.com --- libc/sysdeps/linux/arc/bits/atomic.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)
diff --git a/libc/sysdeps/linux/arc/bits/atomic.h b/libc/sysdeps/linux/arc/bits/atomic.h index 1fdc83f70f6b..48f37879c5c4 100644 --- a/libc/sysdeps/linux/arc/bits/atomic.h +++ b/libc/sysdeps/linux/arc/bits/atomic.h @@ -58,3 +58,27 @@ void __arc_link_error (void);
#define __arch_compare_and_exchange_val_64_acq(mem, newval, oldval) \ ({ __arc_link_error (); oldval; }) + +/* Store NEWVALUE in *MEM and return the old value. + Atomic EX is present in all configurations + */ + +#define __arch_exchange_32_acq(mem, newval) \ + ({ \ + __typeof__(*(mem)) val = newval; \ + \ + __asm__ __volatile__( \ + "ex %0, [%1]" \ + : "+r" (val) \ + : "r" (mem) \ + : "memory" ); \ + \ + val; \ + }) + +#define atomic_exchange_acq(mem, newval) \ + ({ \ + if (sizeof(*(mem)) != 4) \ + abort(); \ + __arch_exchange_32_acq(mem, newval); \ + })
Signed-off-by: Vineet Gupta vgupta@synopsys.com --- extra/Configs/Config.arc | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/extra/Configs/Config.arc b/extra/Configs/Config.arc index 0c0bc71ce2fc..c263dbf46028 100644 --- a/extra/Configs/Config.arc +++ b/extra/Configs/Config.arc @@ -28,6 +28,14 @@ config CONFIG_ARC_CPU_HS
endchoice
+config CONFIG_ARC_HAS_ATOMICS + bool "Support for LLOCK/SCOND instructions" + default y + help + LLOCK/SCOND instructions are needed to implement atomic r-m-w + Otherwise libc needs kernel assisted atomic cmpxchg available + since v4.9 kernel + choice prompt "MMU Page Size" default CONFIG_ARC_PAGE_SIZE_8K
For hardware configurations lacking LLOCK/SCOND (say ARC750), use a syscall to atomically do the cmpxchg. This is costly and painful, but really the only way out.
Note that kenrel only guarantees this to work in a UP configuraion
Reported-by: Avinash Patil avinashp@quantenna.com Signed-off-by: Vineet Gupta vgupta@synopsys.com --- libc/sysdeps/linux/arc/bits/atomic.h | 37 ++++++++++++++++++++++++++++++++++-- 1 file changed, 35 insertions(+), 2 deletions(-)
diff --git a/libc/sysdeps/linux/arc/bits/atomic.h b/libc/sysdeps/linux/arc/bits/atomic.h index 48f37879c5c4..587860964744 100644 --- a/libc/sysdeps/linux/arc/bits/atomic.h +++ b/libc/sysdeps/linux/arc/bits/atomic.h @@ -38,6 +38,11 @@ void __arc_link_error (void); #define __arch_compare_and_exchange_val_16_acq(mem, newval, oldval) \ ({ __arc_link_error (); oldval; })
+#define __arch_compare_and_exchange_val_64_acq(mem, newval, oldval) \ + ({ __arc_link_error (); oldval; }) + +#ifdef __CONFIG_ARC_HAS_ATOMICS__ + #define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval) \ ({ \ __typeof(oldval) prev; \ @@ -56,8 +61,36 @@ void __arc_link_error (void); prev; \ })
-#define __arch_compare_and_exchange_val_64_acq(mem, newval, oldval) \ - ({ __arc_link_error (); oldval; }) +#else + +#ifndef __NR_arc_usr_cmpxchg +#error "__NR_arc_usr_cmpxchg missing: Please upgrade to kernel 4.9+ headers" +#endif + +/* With lack of hardware assist, use kernel to do the atomic operation + This will only work in a UP configuration + */ +#define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval) \ + ({ \ + /* opecode INTERNAL_SYSCALL as it lacks cc clobber */ \ + register int __ret __asm__("r0") = (int)(mem); \ + register int __a1 __asm__("r1") = (int)(oldval); \ + register int __a2 __asm__("r2") = (int)(newval); \ + register int _sys_num __asm__("r8") = __NR_arc_usr_cmpxchg; \ + \ + __asm__ volatile ( \ + ARC_TRAP_INSN \ + : "+r" (__ret) \ + : "r"(_sys_num), "r"(__ret), "r"(__a1), "r"(__a2) \ + : "memory", "cc"); \ + \ + /* syscall returns previous value */ \ + /* Z bit is set if cmpxchg succeeded (we don't use that yet) */ \ + \ + (__typeof(oldval)) __ret; \ + }) + +#endif
/* Store NEWVALUE in *MEM and return the old value. Atomic EX is present in all configurations
-
Vineet Gupta -
Waldemar Brodkorb