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X-BeenThere: tarantool-patches@dev.tarantool.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Sergey Kaplun via Tarantool-patches Reply-To: Sergey Kaplun Cc: tarantool-patches@dev.tarantool.org Errors-To: tarantool-patches-bounces@dev.tarantool.org Sender: "Tarantool-patches" From: Mike Pall Thanks to cuiweixie. (cherry picked from commit b58b07189521e82c7a8e8bc43fc3c271f89832fd) The metamethod for FFI pointer subtraction casts the result value to a 32-bit value, which leads to invalid results. This patch removes the excess cast. Sergey Kaplun: * added the description and the test for the problem Part of tarantool/tarantool#12880 --- Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1449-fix-ptr-diff-64-bit Related issues: * https://github.com/LuaJIT/LuaJIT/issues/1449 * https://github.com/tarantool/tarantool/issues/12880 src/lj_carith.c | 2 +- .../lj-1449-fix-ptr-diff-64-bit.test.lua | 39 +++++++++++++++++++ 2 files changed, 40 insertions(+), 1 deletion(-) create mode 100644 test/tarantool-tests/lj-1449-fix-ptr-diff-64-bit.test.lua diff --git a/src/lj_carith.c b/src/lj_carith.c index eb56d552..3384c2cd 100644 --- a/src/lj_carith.c +++ b/src/lj_carith.c @@ -120,7 +120,7 @@ static int carith_ptr(lua_State *L, CTState *cts, CDArith *ca, MMS mm) /* All valid pointer differences on x64 are in (-2^47, +2^47), ** which fits into a double without loss of precision. */ - setintptrV(L->top-1, (int32_t)diff); + setintptrV(L->top-1, diff); return 1; } else if (mm == MM_lt) { /* Pointer comparison (unsigned). */ setboolV(L->top-1, ((uintptr_t)pp < (uintptr_t)pp2)); diff --git a/test/tarantool-tests/lj-1449-fix-ptr-diff-64-bit.test.lua b/test/tarantool-tests/lj-1449-fix-ptr-diff-64-bit.test.lua new file mode 100644 index 00000000..032b9b4d --- /dev/null +++ b/test/tarantool-tests/lj-1449-fix-ptr-diff-64-bit.test.lua @@ -0,0 +1,39 @@ +local tap = require('tap') + +-- Test file to demonstrate LuaJIT's incorrect 64-bit pointer +-- subtraction. +-- See also: https://github.com/LuaJIT/LuaJIT/issues/1449. + +local test = tap.test('lj-1449-fix-ptr-diff-64-bit') + +local ffi = require('ffi') + +test:plan(2) + +local diff = 0x80000001ULL +local base = 0x700000000000ULL +local p0 = ffi.cast('char *', base) +local p1 = ffi.cast('char *', base + diff) + +test:is(p1 - p0, diff, 'correct pointer difference between 64-bit pointers') + +test:skipcond({ + ['Test requires JIT enabled'] = not jit.status(), +}) + +local results = {} + +jit.opt.start('hotloop=1') + +for i = 1, 4 do + -- Use constants on trace. + local delta = 0x80000001ULL + local b = 0x700000000000ULL + local pt0 = ffi.cast('char *', b) + local pt1 = ffi.cast('char *', b + delta) + results[i] = pt1 - pt0 +end + +test:samevalues(results, 'consistent JIT and VM behaviour for ptr subtraction') + +test:done(true) -- 2.55.0