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#ifndef OS_CPU_LINUX_S390_ATOMIC_LINUX_S390_HPP
#define OS_CPU_LINUX_S390_ATOMIC_LINUX_S390_HPP
#include "runtime/atomic.hpp"
#include "runtime/os.hpp"
#include "runtime/vm_version.hpp"
// Note that the compare-and-swap instructions on System z perform
// a serialization function before the storage operand is fetched
// and again after the operation is completed.
//
// Used constraint modifiers:
// = write-only access: Value on entry to inline-assembler code irrelevant.
// + read/write access: Value on entry is used; on exit value is changed.
// read-only access: Value on entry is used and never changed.
// & early-clobber access: Might be modified before all read-only operands
// have been used.
// a address register operand (not GR0).
// d general register operand (including GR0)
// Q memory operand w/o index register.
// 0..9 operand reference (by operand position).
// Used for operands that fill multiple roles. One example would be a
// write-only operand receiving its initial value from a read-only operand.
// Refer to cmpxchg(..) operand #0 and variable cmp_val for a real-life example.
//
// On System z, all store operations are atomic if the address where the data is stored into
// is an integer multiple of the data length. Furthermore, all stores are ordered:
// a store which occurs conceptually before another store becomes visible to other CPUs
// before the other store becomes visible.
//------------
// Atomic::add
//------------
// These methods force the value in memory to be augmented by the passed increment.
// Both, memory value and increment, are treated as 32bit signed binary integers.
// No overflow exceptions are recognized, and the condition code does not hold
// information about the value in memory.
//
// The value in memory is updated by using a compare-and-swap instruction. The
// instruction is retried as often as required.
//
// The return value of the method is the value that was successfully stored. At the
// time the caller receives back control, the value in memory may have changed already.
// New atomic operations only include specific-operand-serialization, not full
// memory barriers. We can use the Fast-BCR-Serialization Facility for them.
inline void z196_fast_sync() {
__asm__ __volatile__ ("bcr 14, 0" : : : "memory");
}
template<size_t byte_size>
struct Atomic::PlatformAdd
: Atomic::AddAndFetch<Atomic::PlatformAdd<byte_size> >
{
template<typename I, typename D>
D add_and_fetch(I add_value, D volatile* dest, atomic_memory_order order) const;
};
template<>
template<typename I, typename D>
inline D Atomic::PlatformAdd<4>::add_and_fetch(I inc, D volatile* dest,
atomic_memory_order order) const {
STATIC_ASSERT(4 == sizeof(I));
STATIC_ASSERT(4 == sizeof(D));
D old, upd;
if (VM_Version::has_LoadAndALUAtomicV1()) {
if (order == memory_order_conservative) { z196_fast_sync(); }
__asm__ __volatile__ (
" LGFR 0,%[inc] \n\t" // save increment
" LA 3,%[mem] \n\t" // force data address into ARG2
// " LAA %[upd],%[inc],%[mem] \n\t" // increment and get old value
// " LAA 2,0,0(3) \n\t" // actually coded instruction
" .byte 0xeb \n\t" // LAA main opcode
" .byte 0x20 \n\t" // R1,R3
" .byte 0x30 \n\t" // R2,disp1
" .byte 0x00 \n\t" // disp2,disp3
" .byte 0x00 \n\t" // disp4,disp5
" .byte 0xf8 \n\t" // LAA minor opcode
" AR 2,0 \n\t" // calc new value in register
" LR %[upd],2 \n\t" // move to result register
//---< outputs >---
: [upd] "=&d" (upd) // write-only, updated counter value
, [mem] "+Q" (*dest) // read/write, memory to be updated atomically
//---< inputs >---
: [inc] "a" (inc) // read-only.
//---< clobbered >---
: "cc", "r0", "r2", "r3", "memory"
);
if (order == memory_order_conservative) { z196_fast_sync(); }
} else {
__asm__ __volatile__ (
" LLGF %[old],%[mem] \n\t" // get old value
"0: LA %[upd],0(%[inc],%[old]) \n\t" // calc result
" CS %[old],%[upd],%[mem] \n\t" // try to xchg res with mem
" JNE 0b \n\t" // no success? -> retry
//---< outputs >---
: [old] "=&a" (old) // write-only, old counter value
, [upd] "=&d" (upd) // write-only, updated counter value
, [mem] "+Q" (*dest) // read/write, memory to be updated atomically
//---< inputs >---
: [inc] "a" (inc) // read-only.
//---< clobbered >---
: "cc", "memory"
);
}
return upd;
}
template<>
template<typename I, typename D>
inline D Atomic::PlatformAdd<8>::add_and_fetch(I inc, D volatile* dest,
atomic_memory_order order) const {
STATIC_ASSERT(8 == sizeof(I));
STATIC_ASSERT(8 == sizeof(D));
D old, upd;
if (VM_Version::has_LoadAndALUAtomicV1()) {
if (order == memory_order_conservative) { z196_fast_sync(); }
__asm__ __volatile__ (
" LGR 0,%[inc] \n\t" // save increment
" LA 3,%[mem] \n\t" // force data address into ARG2
// " LAAG %[upd],%[inc],%[mem] \n\t" // increment and get old value
// " LAAG 2,0,0(3) \n\t" // actually coded instruction
" .byte 0xeb \n\t" // LAA main opcode
" .byte 0x20 \n\t" // R1,R3
" .byte 0x30 \n\t" // R2,disp1
" .byte 0x00 \n\t" // disp2,disp3
" .byte 0x00 \n\t" // disp4,disp5
" .byte 0xe8 \n\t" // LAA minor opcode
" AGR 2,0 \n\t" // calc new value in register
" LGR %[upd],2 \n\t" // move to result register
//---< outputs >---
: [upd] "=&d" (upd) // write-only, updated counter value
, [mem] "+Q" (*dest) // read/write, memory to be updated atomically
//---< inputs >---
: [inc] "a" (inc) // read-only.
//---< clobbered >---
: "cc", "r0", "r2", "r3", "memory"
);
if (order == memory_order_conservative) { z196_fast_sync(); }
} else {
__asm__ __volatile__ (
" LG %[old],%[mem] \n\t" // get old value
"0: LA %[upd],0(%[inc],%[old]) \n\t" // calc result
" CSG %[old],%[upd],%[mem] \n\t" // try to xchg res with mem
" JNE 0b \n\t" // no success? -> retry
//---< outputs >---
: [old] "=&a" (old) // write-only, old counter value
, [upd] "=&d" (upd) // write-only, updated counter value
, [mem] "+Q" (*dest) // read/write, memory to be updated atomically
//---< inputs >---
: [inc] "a" (inc) // read-only.
//---< clobbered >---
: "cc", "memory"
);
}
return upd;
}
//-------------
// Atomic::xchg
//-------------
// These methods force the value in memory to be replaced by the new value passed
// in as argument.
//
// The value in memory is replaced by using a compare-and-swap instruction. The
// instruction is retried as often as required. This makes sure that the new
// value can be seen, at least for a very short period of time, by other CPUs.
//
// If we would use a normal "load(old value) store(new value)" sequence,
// the new value could be lost unnoticed, due to a store(new value) from
// another thread.
//
// The return value is the (unchanged) value from memory as it was when the
// replacement succeeded.
template<>
template<typename T>
inline T Atomic::PlatformXchg<4>::operator()(T exchange_value,
T volatile* dest,
atomic_memory_order unused) const {
STATIC_ASSERT(4 == sizeof(T));
T old;
__asm__ __volatile__ (
" LLGF %[old],%[mem] \n\t" // get old value
"0: CS %[old],%[upd],%[mem] \n\t" // try to xchg upd with mem
" JNE 0b \n\t" // no success? -> retry
//---< outputs >---
: [old] "=&d" (old) // write-only, prev value irrelevant
, [mem] "+Q" (*dest) // read/write, memory to be updated atomically
//---< inputs >---
: [upd] "d" (exchange_value) // read-only, value to be written to memory
//---< clobbered >---
: "cc", "memory"
);
return old;
}
template<>
template<typename T>
inline T Atomic::PlatformXchg<8>::operator()(T exchange_value,
T volatile* dest,
atomic_memory_order unused) const {
STATIC_ASSERT(8 == sizeof(T));
T old;
__asm__ __volatile__ (
" LG %[old],%[mem] \n\t" // get old value
"0: CSG %[old],%[upd],%[mem] \n\t" // try to xchg upd with mem
" JNE 0b \n\t" // no success? -> retry
//---< outputs >---
: [old] "=&d" (old) // write-only, init from memory
, [mem] "+Q" (*dest) // read/write, memory to be updated atomically
//---< inputs >---
: [upd] "d" (exchange_value) // read-only, value to be written to memory
//---< clobbered >---
: "cc", "memory"
);
return old;
}
//----------------
// Atomic::cmpxchg
//----------------
// These methods compare the value in memory with a given compare value.
// If both values compare equal, the value in memory is replaced with
// the exchange value.
//
// The value in memory is compared and replaced by using a compare-and-swap
// instruction. The instruction is NOT retried (one shot only).
//
// The return value is the (unchanged) value from memory as it was when the
// compare-and-swap instruction completed. A successful exchange operation
// is indicated by (return value == compare_value). If unsuccessful, a new
// exchange value can be calculated based on the return value which is the
// latest contents of the memory location.
//
// Inspecting the return value is the only way for the caller to determine
// if the compare-and-swap instruction was successful:
// - If return value and compare value compare equal, the compare-and-swap
// instruction was successful and the value in memory was replaced by the
// exchange value.
// - If return value and compare value compare unequal, the compare-and-swap
// instruction was not successful. The value in memory was left unchanged.
//
// The s390 processors always fence before and after the csg instructions.
// Thus we ignore the memory ordering argument. The docu says: "A serialization
// function is performed before the operand is fetched and again after the
// operation is completed."
// No direct support for cmpxchg of bytes; emulate using int.
template<>
struct Atomic::PlatformCmpxchg<1> : Atomic::CmpxchgByteUsingInt {};
template<>
template<typename T>
inline T Atomic::PlatformCmpxchg<4>::operator()(T xchg_val,
T volatile* dest,
T cmp_val,
atomic_memory_order unused) const {
STATIC_ASSERT(4 == sizeof(T));
T old;
__asm__ __volatile__ (
" CS %[old],%[upd],%[mem] \n\t" // Try to xchg upd with mem.
// outputs
: [old] "=&d" (old) // Write-only, prev value irrelevant.
, [mem] "+Q" (*dest) // Read/write, memory to be updated atomically.
// inputs
: [upd] "d" (xchg_val)
, "0" (cmp_val) // Read-only, initial value for [old] (operand #0).
// clobbered
: "cc", "memory"
);
return old;
}
template<>
template<typename T>
inline T Atomic::PlatformCmpxchg<8>::operator()(T xchg_val,
T volatile* dest,
T cmp_val,
atomic_memory_order unused) const {
STATIC_ASSERT(8 == sizeof(T));
T old;
__asm__ __volatile__ (
" CSG %[old],%[upd],%[mem] \n\t" // Try to xchg upd with mem.
// outputs
: [old] "=&d" (old) // Write-only, prev value irrelevant.
, [mem] "+Q" (*dest) // Read/write, memory to be updated atomically.
// inputs
: [upd] "d" (xchg_val)
, "0" (cmp_val) // Read-only, initial value for [old] (operand #0).
// clobbered
: "cc", "memory"
);
return old;
}
#endif // OS_CPU_LINUX_S390_ATOMIC_LINUX_S390_HPP