[codegen] --gc:arc does not properly emit cstring, results in SIGSEGV

[zevv]

Code:

let a = "hello".cstring

Default nim generates:

N_LIB_PRIVATE NIM_CONST NCSTRING a__xxx= "hello";

but with --gc:arc this results in:

static  struct {                                                                          
  NI cap; NIM_CHAR data[5+1];                                       
} TM__xxx = { 5 | NIM_STRLIT_FLAG, "hello" };            
N_LIB_PRIVATE NIM_CONST NCSTRING a__yyy = {5, (NimStrPayload*)&TM__xxx};

(mangling replaced by xxx and yyy for readability)

Using the cstring results in a SIGSEGV:

let a = "hello".cstring
echo a

nim c --gc:arc -r t2.nim

==168972== Memcheck, a memory error detector
==168972== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==168972== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==168972== Command: ./t2
==168972== 
==168972== Invalid read of size 1
==168972==    at 0x4839C62: strlen (vg_replace_strmem.c:461)
==168972==    by 0x10A462: nimCStrLen (stdlib_system.nim.c:1089)
==168972==    by 0x10D1A8: cstrToNimstr (stdlib_system.nim.c:2010)
==168972==    by 0x112568: NimMainModule (@mt2.nim.c:153)
==168972==    by 0x11243B: NimMainInner (@mt2.nim.c:119)
==168972==    by 0x112468: NimMain (@mt2.nim.c:127)
==168972==    by 0x1124A2: main (@mt2.nim.c:134)
==168972==  Address 0x5 is not stack'd, malloc'd or (recently) free'd
==168972== 
Traceback (most recent call last)

[zevv]

Is this a valid fix?

diff --git compiler/ccgexprs.nim compiler/ccgexprs.nim
index 10b17663e..632e4bb31 100644
--- compiler/ccgexprs.nim
+++ compiler/ccgexprs.nim
@@ -2974,7 +2974,7 @@ proc genBracedInit(p: BProc, n: PNode; isConst: bool): Rope =
     of tyObject:
       result = genConstObjConstr(p, n, isConst)
     of tyString, tyCString:
-      if optSeqDestructors in p.config.globalOptions and n.kind != nkNilLit:
+      if optSeqDestructors in p.config.globalOptions and n.kind != nkNilLit and ty == tyString:
         result = genStringLiteralV2Const(p.module, n, isConst)
       else:
         var d: TLoc

[Araq]

@zevv I think so, worth a try.