[Tarantool-patches] [PATCH luajit v2 4/6] ARM64: Reorder interpreter stack frame and fix unwinding.

[Maksim Kokryashkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

From: Mike Pall <mike>

Reported by Yichun Zhang. Fixes #722.
May help towards fixing #698, too.

(cherry picked from commit 421c4c798791d27b7f967df39891c4e4fa1d107c)

The `_Unwind_Find_FDE` fails to find the FDE (frame descriptor
element) for `lj_vm_ffi_call` in DWARF unwind info, despite
the presence of its data in the `.debug_frame` section.

LuaJIT emits its own DWARF entries for the CFI (call frame
information, section 6.4.1 in DWARF standard)[1]. Also,
DWARF has the augmentation mechanism, which you can use to
provide additional platform-specific info, which affects unwinder.
Normally, DWARF saves and restores the GPRs and the FPRs in the
natural order, starting with the GPRs. However, LuaJIT has
augmentation segment in emitted debug info, which specifies,
that it saves registers in different order and uses GOT in
PC-relative mode. Those debug entries had incorrect offsets.

Reordering of interpreter stack frame fixes the issue,
making offsets consistent with augmentation and the
DWARF-standard itself.

[1]: https://dwarfstd.org/doc/DWARF5.pdf

Maxim Kokryashkin:
* added the description for the problem

Needed for tarantool/tarantool#6096
Part of tarantool/tarantool#7230
---
>> +|.define SAVE_GPR_, 112 // 112+10*8: 64 bit GPR saves
>
>(Not for change, just random thoughts)
>Why it is not .define SAVE_GPR_, SAVE_FPR_+8*8
>
>> +|.define SAVE_FPR_, 48 // 48+8*8: 64 bit FPR saves
I have no clue whatsoever. It is Mike-way of doing things.
Furthermore, normally, FPRs are stored after the GPRs.

>> +| stp d..fpr2, d..fpr1, [sp, # SAVE_FPR_+(14-fpr1)*8]
>> +| stp x..gpr2, x..gpr1, [sp, # SAVE_GPR_+(27-gpr1)*8]
>
>(Not for change, just random thoughts)
>Should those 14 and 27 magic numbers be a define also, describing the idea
>behind them?
Those a just some register numbers (like x14 or x27). I don't
really think they should be defined. Libunwind has several similar
constructions in its source and nothing is defined there.

 src/lj_frame.h    |  12 +--
 src/vm_arm64.dasc | 189 +++++++++++++++++++++++++++++++++++-----------
 2 files changed, 152 insertions(+), 49 deletions(-)

diff --git a/src/lj_frame.h b/src/lj_frame.h
index 9fd63fa2..1e4adaa3 100644
--- a/src/lj_frame.h
+++ b/src/lj_frame.h
@@ -192,12 +192,12 @@ enum { LJ_CONT_TAILCALL, LJ_CONT_FFI_CALLBACK };  /* Special continuations. */
 #endif
 #define CFRAME_SHIFT_MULTRES	3
 #elif LJ_TARGET_ARM64
-#define CFRAME_OFS_ERRF		196
-#define CFRAME_OFS_NRES		200
-#define CFRAME_OFS_PREV		160
-#define CFRAME_OFS_L		176
-#define CFRAME_OFS_PC		168
-#define CFRAME_OFS_MULTRES	192
+#define CFRAME_OFS_ERRF		36
+#define CFRAME_OFS_NRES		40
+#define CFRAME_OFS_PREV		0
+#define CFRAME_OFS_L		16
+#define CFRAME_OFS_PC		8
+#define CFRAME_OFS_MULTRES	32
 #define CFRAME_SIZE		208
 #define CFRAME_SHIFT_MULTRES	3
 #elif LJ_TARGET_PPC
diff --git a/src/vm_arm64.dasc b/src/vm_arm64.dasc
index 313cc94f..ad57bca3 100644
--- a/src/vm_arm64.dasc
+++ b/src/vm_arm64.dasc
@@ -81,47 +81,49 @@
 |
 |.define CFRAME_SPACE,	208
 |//----- 16 byte aligned, <-- sp entering interpreter
-|// Unused		[sp, #204]	// 32 bit values
-|.define SAVE_NRES,	[sp, #200]
-|.define SAVE_ERRF,	[sp, #196]
-|.define SAVE_MULTRES,	[sp, #192]
-|.define TMPD,		[sp, #184]	// 64 bit values
-|.define SAVE_L,	[sp, #176]
-|.define SAVE_PC,	[sp, #168]
-|.define SAVE_CFRAME,	[sp, #160]
-|.define SAVE_FPR_,	96		// 96+8*8: 64 bit FPR saves
-|.define SAVE_GPR_,	16		// 16+10*8: 64 bit GPR saves
-|.define SAVE_LR,	[sp, #8]
-|.define SAVE_FP,	[sp]
+|.define SAVE_LR,	[sp, #200]
+|.define SAVE_FP,	[sp, #192]
+|.define SAVE_GPR_,	112		// 112+10*8: 64 bit GPR saves
+|.define SAVE_FPR_,	48		// 48+8*8: 64 bit FPR saves
+|// Unused		[sp, #44]	// 32 bit values
+|.define SAVE_NRES,	[sp, #40]
+|.define SAVE_ERRF,	[sp, #36]
+|.define SAVE_MULTRES,	[sp, #32]
+|.define TMPD,		[sp, #24]	// 64 bit values
+|.define SAVE_L,	[sp, #16]
+|.define SAVE_PC,	[sp, #8]
+|.define SAVE_CFRAME,	[sp, #0]
 |//----- 16 byte aligned, <-- sp while in interpreter.
 |
-|.define TMPDofs,	#184
+|.define TMPDofs,	#24
 |
 |.macro save_, gpr1, gpr2, fpr1, fpr2
-|  stp d..fpr1, d..fpr2, [sp, # SAVE_FPR_+(fpr1-8)*8]
-|  stp x..gpr1, x..gpr2, [sp, # SAVE_GPR_+(gpr1-19)*8]
+|  stp d..fpr2, d..fpr1, [sp, # SAVE_FPR_+(14-fpr1)*8]
+|  stp x..gpr2, x..gpr1, [sp, # SAVE_GPR_+(27-gpr1)*8]
 |.endmacro
 |.macro rest_, gpr1, gpr2, fpr1, fpr2
-|  ldp d..fpr1, d..fpr2, [sp, # SAVE_FPR_+(fpr1-8)*8]
-|  ldp x..gpr1, x..gpr2, [sp, # SAVE_GPR_+(gpr1-19)*8]
+|  ldp d..fpr2, d..fpr1, [sp, # SAVE_FPR_+(14-fpr1)*8]
+|  ldp x..gpr2, x..gpr1, [sp, # SAVE_GPR_+(27-gpr1)*8]
 |.endmacro
 |
 |.macro saveregs
-|  stp fp, lr, [sp, #-CFRAME_SPACE]!
+|  sub sp, sp, # CFRAME_SPACE
+|  stp fp, lr, SAVE_FP
 |  add fp, sp, #0
-|  stp x19, x20, [sp, # SAVE_GPR_]
+|  stp x20, x19, [sp, # SAVE_GPR_+(27-19)*8]
 |  save_ 21, 22, 8, 9
 |  save_ 23, 24, 10, 11
 |  save_ 25, 26, 12, 13
 |  save_ 27, 28, 14, 15
 |.endmacro
 |.macro restoreregs
-|  ldp x19, x20, [sp, # SAVE_GPR_]
+|  ldp x20, x19, [sp, # SAVE_GPR_+(27-19)*8]
 |  rest_ 21, 22, 8, 9
 |  rest_ 23, 24, 10, 11
 |  rest_ 25, 26, 12, 13
 |  rest_ 27, 28, 14, 15
-|  ldp fp, lr, [sp], # CFRAME_SPACE
+|  ldp fp, lr, SAVE_FP
+|  add sp, sp, # CFRAME_SPACE
 |.endmacro
 |
 |// Type definitions. Some of these are only used for documentation.
@@ -2125,9 +2127,9 @@ static void build_subroutines(BuildCtx *ctx)
   |  // Caveat: needs special frame unwinding, see below.
   |.if FFI
   |  .type CCSTATE, CCallState, x19
-  |  stp fp, lr, [sp, #-32]!
+  |  stp x20, CCSTATE, [sp, #-32]!
+  |  stp fp, lr, [sp, #16]
   |  add fp, sp, #0
-  |  str CCSTATE, [sp, #16]
   |  mov CCSTATE, x0
   |  ldr TMP0w, CCSTATE:x0->spadj
   |   ldrb TMP1w, CCSTATE->nsp
@@ -2156,8 +2158,8 @@ static void build_subroutines(BuildCtx *ctx)
   |  stp x0, x1, CCSTATE->gpr[0]
   |   stp d0, d1, CCSTATE->fpr[0]
   |   stp d2, d3, CCSTATE->fpr[2]
-  |  ldr CCSTATE, [sp, #16]
-  |  ldp fp, lr, [sp], #32
+  |  ldp fp, lr, [sp, #16]
+  |  ldp x20, CCSTATE, [sp], #32
   |  ret
   |.endif
   |// Note: vm_ffi_call must be the last function in this object file!
@@ -2887,7 +2889,7 @@ static void build_ins(BuildCtx *ctx, BCOp op, int defop)
   case BC_GGET:
     |  // RA = dst, RC = str_const (~)
   case BC_GSET:
-    |  // RA = dst, RC = str_const (~)
+    |  // RA = src, RC = str_const (~)
     |  ldr LFUNC:CARG1, [BASE, FRAME_FUNC]
     |   mvn RC, RC
     |  and LFUNC:CARG1, CARG1, #LJ_GCVMASK
@@ -3863,7 +3865,7 @@ static int build_backend(BuildCtx *ctx)
 static void emit_asm_debug(BuildCtx *ctx)
 {
   int fcofs = (int)((uint8_t *)ctx->glob[GLOB_vm_ffi_call] - ctx->code);
-  int i, cf = CFRAME_SIZE >> 3;
+  int i;
   switch (ctx->mode) {
   case BUILD_elfasm:
     fprintf(ctx->fp, "\t.section .debug_frame,\"\",%%progbits\n");
@@ -3888,14 +3890,14 @@ static void emit_asm_debug(BuildCtx *ctx)
 	"\t.quad .Lbegin\n"
 	"\t.quad %d\n"
 	"\t.byte 0xe\n\t.uleb128 %d\n"		/* def_cfa_offset */
-	"\t.byte 0x9d\n\t.uleb128 %d\n"		/* offset fp */
-	"\t.byte 0x9e\n\t.uleb128 %d\n",	/* offset lr */
-	fcofs, CFRAME_SIZE, cf, cf-1);
+	"\t.byte 0x9e\n\t.uleb128 1\n"		/* offset lr */
+	"\t.byte 0x9d\n\t.uleb128 2\n",		/* offset fp */
+	fcofs, CFRAME_SIZE);
     for (i = 19; i <= 28; i++)  /* offset x19-x28 */
-      fprintf(ctx->fp, "\t.byte 0x%x\n\t.uleb128 %d\n", 0x80+i, cf-i+17);
+      fprintf(ctx->fp, "\t.byte 0x%x\n\t.uleb128 %d\n", 0x80+i, i+(3-19));
     for (i = 8; i <= 15; i++)  /* offset d8-d15 */
       fprintf(ctx->fp, "\t.byte 5\n\t.uleb128 0x%x\n\t.uleb128 %d\n",
-	      64+i, cf-i-4);
+	      64+i, i+(3+(28-19+1)-8));
     fprintf(ctx->fp,
 	"\t.align 3\n"
 	".LEFDE0:\n\n");
@@ -3908,9 +3910,11 @@ static void emit_asm_debug(BuildCtx *ctx)
 	"\t.quad lj_vm_ffi_call\n"
 	"\t.quad %d\n"
 	"\t.byte 0xe\n\t.uleb128 32\n"		/* def_cfa_offset */
-	"\t.byte 0x9d\n\t.uleb128 4\n"		/* offset fp */
-	"\t.byte 0x9e\n\t.uleb128 3\n"		/* offset lr */
-	"\t.byte 0x93\n\t.uleb128 2\n"		/* offset x19 */
+	"\t.byte 0x9e\n\t.uleb128 1\n"		/* offset lr */
+	"\t.byte 0x9d\n\t.uleb128 2\n"		/* offset fp */
+	"\t.byte 0x93\n\t.uleb128 3\n"		/* offset x19 */
+	"\t.byte 0x94\n\t.uleb128 4\n"		/* offset x20 */
+	"\t.byte 0xd\n\t.uleb128 0x1d\n"	/* def_cfa_register fp */
 	"\t.align 3\n"
 	".LEFDE1:\n\n", (int)ctx->codesz - fcofs);
 #endif
@@ -3941,14 +3945,14 @@ static void emit_asm_debug(BuildCtx *ctx)
 	"\t.long %d\n"
 	"\t.uleb128 0\n"			/* augmentation length */
 	"\t.byte 0xe\n\t.uleb128 %d\n"		/* def_cfa_offset */
-	"\t.byte 0x9d\n\t.uleb128 %d\n"		/* offset fp */
-	"\t.byte 0x9e\n\t.uleb128 %d\n",	/* offset lr */
-	fcofs, CFRAME_SIZE, cf, cf-1);
+	"\t.byte 0x9e\n\t.uleb128 1\n"		/* offset lr */
+	"\t.byte 0x9d\n\t.uleb128 2\n",		/* offset fp */
+	fcofs, CFRAME_SIZE);
     for (i = 19; i <= 28; i++)  /* offset x19-x28 */
-      fprintf(ctx->fp, "\t.byte 0x%x\n\t.uleb128 %d\n", 0x80+i, cf-i+17);
+      fprintf(ctx->fp, "\t.byte 0x%x\n\t.uleb128 %d\n", 0x80+i, i+(3-19));
     for (i = 8; i <= 15; i++)  /* offset d8-d15 */
       fprintf(ctx->fp, "\t.byte 5\n\t.uleb128 0x%x\n\t.uleb128 %d\n",
-	      64+i, cf-i-4);
+	      64+i, i+(3+(28-19+1)-8));
     fprintf(ctx->fp,
 	"\t.align 3\n"
 	".LEFDE2:\n\n");
@@ -3977,13 +3981,112 @@ static void emit_asm_debug(BuildCtx *ctx)
 	"\t.long %d\n"
 	"\t.uleb128 0\n"			/* augmentation length */
 	"\t.byte 0xe\n\t.uleb128 32\n"		/* def_cfa_offset */
-	"\t.byte 0x9d\n\t.uleb128 4\n"		/* offset fp */
-	"\t.byte 0x9e\n\t.uleb128 3\n"		/* offset lr */
-	"\t.byte 0x93\n\t.uleb128 2\n"		/* offset x19 */
+	"\t.byte 0x9e\n\t.uleb128 1\n"		/* offset lr */
+	"\t.byte 0x9d\n\t.uleb128 2\n"		/* offset fp */
+	"\t.byte 0x93\n\t.uleb128 3\n"		/* offset x19 */
+	"\t.byte 0x94\n\t.uleb128 4\n"		/* offset x20 */
+	"\t.byte 0xd\n\t.uleb128 0x1d\n"	/* def_cfa_register fp */
 	"\t.align 3\n"
 	".LEFDE3:\n\n", (int)ctx->codesz - fcofs);
 #endif
     break;
+#if !LJ_NO_UNWIND
+  case BUILD_machasm: {
+#if LJ_HASFFI
+    int fcsize = 0;
+#endif
+    int j;
+    fprintf(ctx->fp, "\t.section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support\n");
+    fprintf(ctx->fp,
+	"EH_frame1:\n"
+	"\t.set L$set$x,LECIEX-LSCIEX\n"
+	"\t.long L$set$x\n"
+	"LSCIEX:\n"
+	"\t.long 0\n"
+	"\t.byte 0x1\n"
+	"\t.ascii \"zPR\\0\"\n"
+	"\t.byte 0x1\n"
+	"\t.byte 128-8\n"
+	"\t.byte 30\n"				/* Return address is in lr. */
+	"\t.byte 6\n"				/* augmentation length */
+	"\t.byte 0x9b\n"			/* indirect|pcrel|sdata4 */
+	"\t.long _lj_err_unwind_dwarf@GOTPCREL\n"
+	"\t.byte 0x1b\n"			/* pcrel|sdata4 */
+	"\t.byte 0xc\n\t.byte 31\n\t.byte 0\n"	/* def_cfa sp */
+	"\t.align 3\n"
+	"LECIEX:\n\n");
+    for (j = 0; j < ctx->nsym; j++) {
+      const char *name = ctx->sym[j].name;
+      int32_t size = ctx->sym[j+1].ofs - ctx->sym[j].ofs;
+      if (size == 0) continue;
+#if LJ_HASFFI
+      if (!strcmp(name, "_lj_vm_ffi_call")) { fcsize = size; continue; }
+#endif
+      fprintf(ctx->fp,
+	"%s.eh:\n"
+	"LSFDE%d:\n"
+	"\t.set L$set$%d,LEFDE%d-LASFDE%d\n"
+	"\t.long L$set$%d\n"
+	"LASFDE%d:\n"
+	"\t.long LASFDE%d-EH_frame1\n"
+	"\t.long %s-.\n"
+	"\t.long %d\n"
+	"\t.byte 0\n"				/* augmentation length */
+	"\t.byte 0xe\n\t.byte %d\n\t.byte 1\n"	/* def_cfa_offset */
+	"\t.byte 0x9e\n\t.byte 1\n"		/* offset lr */
+	"\t.byte 0x9d\n\t.byte 2\n",		/* offset fp */
+	name, j, j, j, j, j, j, j, name, size, CFRAME_SIZE);
+      for (i = 19; i <= 28; i++)  /* offset x19-x28 */
+	fprintf(ctx->fp, "\t.byte 0x%x\n\t.byte %d\n", 0x80+i, i+(3-19));
+      for (i = 8; i <= 15; i++)  /* offset d8-d15 */
+	fprintf(ctx->fp, "\t.byte 5\n\t.byte 0x%x\n\t.byte %d\n",
+		64+i, i+(3+(28-19+1)-8));
+      fprintf(ctx->fp,
+	"\t.align 3\n"
+	"LEFDE%d:\n\n", j);
+    }
+#if LJ_HASFFI
+    if (fcsize) {
+      fprintf(ctx->fp,
+	"EH_frame2:\n"
+	"\t.set L$set$y,LECIEY-LSCIEY\n"
+	"\t.long L$set$y\n"
+	"LSCIEY:\n"
+	"\t.long 0\n"
+	"\t.byte 0x1\n"
+	"\t.ascii \"zR\\0\"\n"
+	"\t.byte 0x1\n"
+	"\t.byte 128-8\n"
+	"\t.byte 30\n"				/* Return address is in lr. */
+	"\t.byte 1\n"				/* augmentation length */
+	"\t.byte 0x1b\n"			/* pcrel|sdata4 */
+	"\t.byte 0xc\n\t.byte 31\n\t.byte 0\n"	/* def_cfa sp */
+	"\t.align 3\n"
+	"LECIEY:\n\n");
+      fprintf(ctx->fp,
+	"_lj_vm_ffi_call.eh:\n"
+	"LSFDEY:\n"
+	"\t.set L$set$yy,LEFDEY-LASFDEY\n"
+	"\t.long L$set$yy\n"
+	"LASFDEY:\n"
+	"\t.long LASFDEY-EH_frame2\n"
+	"\t.long _lj_vm_ffi_call-.\n"
+	"\t.long %d\n"
+	"\t.byte 0\n"				/* augmentation length */
+	"\t.byte 0xe\n\t.byte 32\n"		/* def_cfa_offset */
+	"\t.byte 0x9e\n\t.byte 1\n"		/* offset lr */
+	"\t.byte 0x9d\n\t.byte 2\n"		/* offset fp */
+	"\t.byte 0x93\n\t.byte 3\n"		/* offset x19 */
+	"\t.byte 0x94\n\t.byte 4\n"		/* offset x20 */
+	"\t.byte 0xd\n\t.uleb128 0x1d\n"	/* def_cfa_register fp */
+	"\t.align 3\n"
+	"LEFDEY:\n\n", fcsize);
+    }
+#endif
+    fprintf(ctx->fp, ".subsections_via_symbols\n");
+    }
+    break;
+#endif
   default:
     break;
   }
--
2.32.1 (Apple Git-133)