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Re: [PATCH v4] tcg: Toggle page execution for Apple Silicon


From: BALATON Zoltan
Subject: Re: [PATCH v4] tcg: Toggle page execution for Apple Silicon
Date: Sat, 23 Jan 2021 19:33:37 +0100 (CET)

On Sat, 23 Jan 2021, Roman Bolshakov wrote:
On Sat, Jan 23, 2021 at 02:53:49PM +0300, Roman Bolshakov wrote:
On Thu, Jan 21, 2021 at 08:47:52AM -1000, Richard Henderson wrote:
From: Roman Bolshakov <r.bolshakov@yadro.com>

Pages can't be both write and executable at the same time on Apple
Silicon. macOS provides public API to switch write protection [1] for
JIT applications, like TCG.

1. 
https://developer.apple.com/documentation/apple_silicon/porting_just-in-time_compilers_to_apple_silicon

Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Message-Id: <20210113032806.18220-1-r.bolshakov@yadro.com>
[rth: Inline the qemu_thread_jit_* functions;
 drop the MAP_JIT change for a follow-on patch.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---

Supercedes: <20210113032806.18220-1-r.bolshakov@yadro.com>

This is the version of Roman's patch that I'm queuing to tcg-next.
What's missing from the full "Fix execution" patch is setting MAP_JIT
for !splitwx in alloc_code_gen_buffer().


Richard, thanks for updating the patch. I have no objections against
moving the functions and inlining them. However I'm seeing an issue that
wasn't present in v3:

Process 37109 stopped                                                           
                                                               * thread #6, 
stop reason = EXC_BAD_ACCESS (code=1, address=0xfffffffffffffd4f)
    frame #0: 0x00000001002f1c90 
qemu-system-x86_64`tcg_emit_op(opc=INDEX_op_add_i64) at tcg.c:2531:5 [opt]      
                                 2528 TCGOp *tcg_emit_op(TCGOpcode opc)
   2529 {                                                                       
                                                                  2530     
TCGOp *op = tcg_op_alloc(opc);
-> 2531     QTAILQ_INSERT_TAIL(&tcg_ctx->ops, op, link);
   2532     return op;
   2533 }
   2534
Target 0: (qemu-system-x86_64) stopped.
(lldb) bt
* thread #6, stop reason = EXC_BAD_ACCESS (code=1, address=0xfffffffffffffd4f)
  * frame #0: 0x00000001002f1c90 
qemu-system-x86_64`tcg_emit_op(opc=INDEX_op_add_i64) at tcg.c:2531:5 [opt]
    frame #1: 0x000000010026f040 qemu-system-x86_64`tcg_gen_addi_i64 [inlined] 
tcg_gen_op3(opc=INDEX_op_add_i64, a1=4430334952, a2=4430333440,
a3=4430361496) at tcg-op.c:60:17 [opt]
    frame #2: 0x000000010026f038 qemu-system-x86_64`tcg_gen_addi_i64 [inlined] 
tcg_gen_op3_i64(opc=INDEX_op_add_i64, a1=<unavailable>, a2=<unav
ailable>, a3=<unavailable>) at tcg-op.h:94 [opt]
    frame #3: 0x000000010026f030 qemu-system-x86_64`tcg_gen_addi_i64 [inlined] 
tcg_gen_add_i64(ret=<unavailable>, arg1=<unavailable>, arg2=<una
vailable>) at tcg-op.h:618 [opt]
    frame #4: 0x000000010026f030 qemu-system-x86_64`tcg_gen_addi_i64(ret=<unavailable>, 
arg1=<unavailable>, arg2=<unavailable>) at tcg-op.c:123
5 [opt]
    frame #5: 0x000000010021d1e0 
qemu-system-x86_64`gen_lea_modrm_1(s=<unavailable>, a=(def_seg = 2, base = 5, 
index = -1, scale = 0, disp = -6
89)) at translate.c:2101:9 [opt]
    frame #6: 0x000000010020eeec qemu-system-x86_64`disas_insn [inlined] 
gen_lea_modrm(env=0x0000000118610870, s=0x00000001700b6b00, modrm=<una
vailable>) at translate.c:2111:15 [opt]
    frame #7: 0x000000010020eec0 qemu-system-x86_64`disas_insn(s=0x00000001700b6b00, 
cpu=<unavailable>) at translate.c:5509 [opt]
    frame #8: 0x000000010020bb44 
qemu-system-x86_64`i386_tr_translate_insn(dcbase=0x00000001700b6b00, 
cpu=<unavailable>) at translate.c:8573:15
 [opt]
    frame #9: 0x00000001002fbcf8 
qemu-system-x86_64`translator_loop(ops=0x0000000100b209c8, 
db=0x00000001700b6b00, cpu=0x0000000118608000, tb=0
x0000000120017200, max_insns=512) at translator.c:0 [opt]
    frame #10: 0x000000010020b73c 
qemu-system-x86_64`gen_intermediate_code(cpu=<unavailable>, tb=<unavailable>, 
max_insns=<unavailable>) at tra
nslate.c:8635:5 [opt]
    frame #11: 0x0000000100257970 
qemu-system-x86_64`tb_gen_code(cpu=0x0000000118608000, pc=<unavailable>, 
cs_base=0, flags=4194483, cflags=-16
777216) at translate-all.c:1931:5 [opt]
    frame #12: 0x00000001002deb90 qemu-system-x86_64`cpu_exec [inlined] 
tb_find(cpu=0x0000000118608000, last_tb=0x0000000000000000, tb_exit=<un
available>, cf_mask=0) at cpu-exec.c:456:14 [opt]
    frame #13: 0x00000001002deb54 
qemu-system-x86_64`cpu_exec(cpu=0x0000000118608000) at cpu-exec.c:812 [opt]
    frame #14: 0x00000001002bc0d0 
qemu-system-x86_64`tcg_cpus_exec(cpu=0x0000000118608000) at tcg-cpus.c:57:11 
[opt]
    frame #15: 0x000000010024c2cc 
qemu-system-x86_64`rr_cpu_thread_fn(arg=<unavailable>) at tcg-cpus-rr.c:217:21 
[opt]
    frame #16: 0x00000001004b00b4 
qemu-system-x86_64`qemu_thread_start(args=<unavailable>) at 
qemu-thread-posix.c:521:9 [opt]
    frame #17: 0x0000000191c4d06c libsystem_pthread.dylib`_pthread_start + 320

I'm looking into the issue but perhaps we'll need v5.


Nope. The issue is not directly related to the patch and W^X. I think it
can be applied.

tcg_ctx->ops is somehow getting corrupted despite it's initialized
properly during TCG start:

(lldb) p tcg_ctx->ops
(TCGContext::(anonymous union)) $18 = {
 tqh_first = 0x0000008401010000
 tqh_circ = {
   tql_next = 0x0000008401010000
   tql_prev = 0xfffffffffffffd4f
 }
}

I've bisected it (with v3 of Apple Silicon fix for TCG) to:

commit 8fe35e0444be88de4e3ab80a2a0e210a1f6d663d
Author: Richard Henderson <richard.henderson@linaro.org>
Date:   Mon Mar 30 20:42:43 2020 -0700

   tcg/optimize: Use tcg_constant_internal with constant folding

Yes, known problem, see https://bugs.launchpad.net/qemu/+bug/1912065

Regards,
BALATON Zoltan

   Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/optimize.c | 108 ++++++++++++++++++++++++++-------------------------------
1 file changed, 49 insertions(+), 59 deletions(-)

Although, it crashes with a bit different backtrace than provided above:

Process 17251 stopped
* thread #6, stop reason = EXC_BAD_ACCESS (code=1, address=0x10)
   frame #0: 0x00000001002727a8 qemu-system-x86_64`tcg_opt_gen_mov [inlined] 
ts_is_copy(ts=<unavailable>) at optimize.c:68:25 [opt]
  65
  66   static inline bool ts_is_copy(TCGTemp *ts)
  67   {
-> 68       return ts_info(ts)->next_copy != ts;
  69   }
  70
  71   /* Reset TEMP's state, possibly removing the temp for the list of 
copies.  */
Target 0: (qemu-system-x86_64) stopped.
(lldb) bt
* thread #6, stop reason = EXC_BAD_ACCESS (code=1, address=0x10)
 * frame #0: 0x00000001002727a8 qemu-system-x86_64`tcg_opt_gen_mov [inlined] 
ts_is_copy(ts=<unavailable>) at optimize.c:68:25 [opt]
   frame #1: 0x00000001002727a4 qemu-system-x86_64`tcg_opt_gen_mov [inlined] 
ts_are_copies(ts1=0x00000001202e8e50, ts2=0x00000001202ef398) at optimize.c:163 
[opt]
   frame #2: 0x000000010027278c 
qemu-system-x86_64`tcg_opt_gen_mov(s=0x00000001202e8000, op=0x0000000119157710, 
dst=4834889296, src=4834915224) at optimize.c:191 [opt]
   frame #3: 0x0000000100271740 
qemu-system-x86_64`tcg_optimize(s=<unavailable>) at optimize.c:0:9 [opt]
   frame #4: 0x00000001002f39c4 
qemu-system-x86_64`tcg_gen_code(s=0x00000001202e8000, tb=0x0000000128020800) at 
tcg.c:4407:5 [opt]
   frame #5: 0x00000001002b2688 
qemu-system-x86_64`tb_gen_code(cpu=0x0000000118428000, pc=<unavailable>, 
cs_base=0, flags=4194483, cflags=-16777216) at translate-all.c:1961:21 [opt]
   frame #6: 0x0000000100279460 qemu-system-x86_64`cpu_exec [inlined] 
tb_find(cpu=0x0000000118428000, last_tb=0x0000000000000000, 
tb_exit=<unavailable>, cf_mask=0) at cpu-exec.c:456:14 [opt]
   frame #7: 0x0000000100279424 
qemu-system-x86_64`cpu_exec(cpu=0x0000000118428000) at cpu-exec.c:812 [opt]
   frame #8: 0x000000010026ea74 
qemu-system-x86_64`tcg_cpus_exec(cpu=0x0000000118428000) at tcg-cpus.c:57:11 
[opt]
   frame #9: 0x0000000100284efc 
qemu-system-x86_64`rr_cpu_thread_fn(arg=<unavailable>) at tcg-cpus-rr.c:217:21 
[opt]
   frame #10: 0x00000001004cffe8 
qemu-system-x86_64`qemu_thread_start(args=<unavailable>) at 
qemu-thread-posix.c:521:9 [opt]
   frame #11: 0x0000000191c4d06c libsystem_pthread.dylib`_pthread_start + 320

The problem is that ts2 in ts_are_copies() contains NULL state_ptr:

(lldb) p *ts2
(TCGTemp) $2 = {
 reg = TCG_REG_X0
 val_type = TEMP_VAL_DEAD
 base_type = TCG_TYPE_I64
 type = TCG_TYPE_I64
 kind = TEMP_CONST
 indirect_reg = 0
 indirect_base = 0
 mem_coherent = 0
 mem_allocated = 0
 temp_allocated = 1
 val = -690
 mem_base = 0x0000000000000000
 mem_offset = 0
 name = 0x0000000000000000
 state = 0
 state_ptr = 0x0000000000000000
}

-Roman





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