From: Maxim Kokryashkin via Tarantool-patches <tarantool-patches@dev.tarantool.org> To: tarantool-patches@dev.tarantool.org, skaplun@tarantool.org, sergeyb@tarantool.org Subject: [Tarantool-patches] [PATCH luajit v2] Fix snapshot PC when linking to BC_JLOOP that was a BC_RET*. Date: Fri, 29 Sep 2023 16:38:29 +0300 [thread overview] Message-ID: <20230929133843.535217-1-m.kokryashkin@tarantool.org> (raw) From: Mike Pall <mike> Reported by Arseny Vakhrushev. Fix contributed by Peter Cawley. As specified in the comment in `lj_record_stop`, all loops must set `J->pc` to the next instruction. However, the chunk of logic in `lj_trace_exit` expects it to be set to `BC_JLOOP` itself if it used to be a `BC_RET`. This wrong pc results in the execution of random data that goes after `BC_JLOOP` in the case of restoration from the snapshot. This patch fixes that behavior by adapting the loop recording logic to this specific case. Maxim Kokryashkin: * added the description and the test for the problem Part of tarantool/tarantool#8825 --- Changes in v2: - Fixed comments as per review by Sergey Kaplun Branch: https://github.com/tarantool/luajit/tree/fckxorg/lj-624-jloop-snapshot-pc PR: https://github.com/tarantool/tarantool/pull/9166 src/lj_record.c | 9 ++- src/lj_snap.c | 3 + .../lj-624-jloop-snapshot-pc.test.lua | 81 +++++++++++++++++++ 3 files changed, 89 insertions(+), 4 deletions(-) create mode 100644 test/tarantool-tests/lj-624-jloop-snapshot-pc.test.lua diff --git a/src/lj_record.c b/src/lj_record.c index 48a5481b..3bdc6134 100644 --- a/src/lj_record.c +++ b/src/lj_record.c @@ -570,10 +570,10 @@ static LoopEvent rec_iterl(jit_State *J, const BCIns iterins) } /* Record LOOP/JLOOP. Now, that was easy. */ -static LoopEvent rec_loop(jit_State *J, BCReg ra) +static LoopEvent rec_loop(jit_State *J, BCReg ra, int skip) { if (ra < J->maxslot) J->maxslot = ra; - J->pc++; + J->pc += skip; return LOOPEV_ENTER; } @@ -2433,7 +2433,7 @@ void lj_record_ins(jit_State *J) rec_loop_interp(J, pc, rec_iterl(J, *pc)); break; case BC_LOOP: - rec_loop_interp(J, pc, rec_loop(J, ra)); + rec_loop_interp(J, pc, rec_loop(J, ra, 1)); break; case BC_JFORL: @@ -2443,7 +2443,8 @@ void lj_record_ins(jit_State *J) rec_loop_jit(J, rc, rec_iterl(J, traceref(J, rc)->startins)); break; case BC_JLOOP: - rec_loop_jit(J, rc, rec_loop(J, ra)); + rec_loop_jit(J, rc, rec_loop(J, ra, + !bc_isret(bc_op(traceref(J, rc)->startins)))); break; case BC_IFORL: diff --git a/src/lj_snap.c b/src/lj_snap.c index 2dc281cb..b50ecfb2 100644 --- a/src/lj_snap.c +++ b/src/lj_snap.c @@ -115,6 +115,9 @@ static MSize snapshot_framelinks(jit_State *J, SnapEntry *map, uint8_t *topslot) #else MSize f = 0; map[f++] = SNAP_MKPC(J->pc); /* The current PC is always the first entry. */ + lj_assertJ(!J->pt || + (J->pc >= proto_bc(J->pt) && + J->pc < proto_bc(J->pt) + J->pt->sizebc), "bad snapshot PC"); #endif while (frame > lim) { /* Backwards traversal of all frames above base. */ if (frame_islua(frame)) { diff --git a/test/tarantool-tests/lj-624-jloop-snapshot-pc.test.lua b/test/tarantool-tests/lj-624-jloop-snapshot-pc.test.lua new file mode 100644 index 00000000..e0c1fa81 --- /dev/null +++ b/test/tarantool-tests/lj-624-jloop-snapshot-pc.test.lua @@ -0,0 +1,81 @@ +local tap = require('tap') +local test = tap.test('lj-624-jloop-snapshot-pc'):skipcond({ + ['Test requires JIT enabled'] = not jit.status(), +}) + +test:plan(1) +-- XXX: The test case below triggers the assertion that was +-- added in the patch if tested without the fix itself. It +-- is hard to create a stable reproducer without turning off +-- ASLR and VM randomizations, which is not suitable for testing. + +-- Reproducer below produces the following traces: +-- ---- TRACE 1 start test.lua:2 +-- 0001 KSHORT 1 2 +-- 0002 ISGE 0 1 +-- 0003 JMP 1 => 0006 +-- 0006 UGET 1 0 ; fib +-- 0007 SUBVN 2 0 0 ; 1 +-- 0008 CALL 1 2 2 +-- 0000 . FUNCF 4 ; test.lua:2 +-- 0001 . KSHORT 1 2 +-- 0002 . ISGE 0 1 +-- 0003 . JMP 1 => 0006 +-- 0006 . UGET 1 0 ; fib +-- 0007 . SUBVN 2 0 0 ; 1 +-- 0008 . CALL 1 2 2 +-- 0000 . . FUNCF 4 ; test.lua:2 +-- 0001 . . KSHORT 1 2 +-- 0002 . . ISGE 0 1 +-- 0003 . . JMP 1 => 0006 +-- 0006 . . UGET 1 0 ; fib +-- 0007 . . SUBVN 2 0 0 ; 1 +-- 0008 . . CALL 1 2 2 +-- 0000 . . . FUNCF 4 ; test.lua:2 +-- ---- TRACE 1 stop -> up-recursion +-- +-- ---- TRACE 1 exit 1 +-- ---- TRACE 2 start 1/1 test.lua:3 +-- 0004 ISTC 1 0 +-- 0005 JMP 1 => 0013 +-- 0013 RET1 1 2 +-- 0009 UGET 2 0 ; fib +-- 0010 SUBVN 3 0 1 ; 2 +-- 0011 CALL 2 2 2 +-- 0000 . JFUNCF 4 1 ; test.lua:2 +-- ---- TRACE 2 stop -> 1 +-- +-- ---- TRACE 2 exit 1 +-- ---- TRACE 3 start 2/1 test.lua:3 +-- 0013 RET1 1 2 +-- 0012 ADDVV 1 1 2 +-- 0013 RET1 1 2 +-- ---- TRACE 3 abort test.lua:3 -- down-recursion, restarting +-- +-- ---- TRACE 3 start test.lua:3 +-- 0013 RET1 1 2 +-- 0009 UGET 2 0 ; fib +-- 0010 SUBVN 3 0 1 ; 2 +-- 0011 CALL 2 2 2 +-- 0000 . JFUNCF 4 1 ; test.lua:2 +-- ---- TRACE 3 stop -> 1 +-- +-- ---- TRACE 2 exit 1 +-- ---- TRACE 4 start 2/1 test.lua:3 +-- 0013 RET1 1 2 +-- 0012 ADDVV 1 1 2 +-- 0013 JLOOP 3 3 +-- +-- During the recording of the latter JLOOP the assertion added +-- in the patch is triggered. + + +jit.opt.start('hotloop=1', 'hotexit=1') +local function fib(n) + return n < 2 and n or fib(n - 1) + fib(n - 2) +end + +fib(5) + +test:ok(true, 'snapshot pc is correct') +test:done(true) -- 2.42.0
next reply other threads:[~2023-09-29 13:38 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-09-29 13:38 Maxim Kokryashkin via Tarantool-patches [this message] 2023-10-03 18:31 ` Sergey Bronnikov via Tarantool-patches
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