gc:arc - SIGSEGV for rawAlloc on windows

[SFR0815]

Hi!

This replaces issue #15954.

Example

I execute a_label.nim (see https://gist.github.com/SFR0815/59cf9a9be74fec43be01a46a0f53a47d) and execute using

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

using

$ nim -v
Nim Compiler Version 1.4.2 [Windows: amd64] 
Compiled at 2020-11-30
Copyright (c) 2006-2020 by Andreas 

Current Output

[Suite] Uiapi List - SubEntitySelectionList 
[OK]  .. 1 
[OK]  .. 2      
[OK]  .. 3   
[OK]  .. 4    
[OK]  .. 5     
[OK]  .. 6      
[OK]  .. 7 
Traceback (most recent call last)                                                                                                                                                                                                                                                                                        ...\ut_label.nim(145) ut_label       
...\ut_label.nim(100) doSomething           
...\iso8601.nim(399) getDateTime  
...\.choosenim\toolchains\nim-1.4.2\lib\pure\times.nim(1643) initTimeFormat                                                                                                                                                                                                                                   SIGSEGV: Illegal storage access. (Attempt to read from nil?)

Expected Output

... like executing using nim c -r a_label.nim ...

[Suite] Uiapi List - SubEntitySelectionList       
[OK]  .. 1   
[OK]  .. 2     
[OK]  .. 3    
[OK]  .. 4  
[OK]  .. 5      
[OK]  .. 6
[OK]  .. 7   
[OK]  .. 8         
[OK]  .. 9        
[OK]  .. 10   
[OK]  .. 11      
[OK]  .. 12      
[OK]  .. 13    
[OK]  .. 14       
[OK]  .. 15        
[OK]  .. 16              
[OK]  .. 17        
[OK]  .. 18

Possible Solution

[timotheecour]

• what happens with nim c -r a_label.nim
• can you minimize as much as possible the code in https://gist.github.com/SFR0815/59cf9a9be74fec43be01a46a0f53a47d ? this will help everyone (and is needed anyway)

[LucasUllon]

compiling the file with nim c --gc: arc -d: useMalloc -g ut_label.nim and using valgrind to see exactly where the code fails you get this: https://gist.github.com/LucasUllon/a55a8f54b0876ac8466d524085362111

[timotheecour]

that's good but I mean minimizing the source code to get a minimum reproducible example, as is the case for most other issues that are reported in this repo

[SFR0815]

1. ad nim c -r a_label.nim: Executes the test as above without any error. No issue in practice. Everything works nicely.

2. ad minimization:
   Hope the following is short enough:

Example

import 
  unittest, strutils

proc getShortName(
              name: string
              ): string =
  result = name
  result.removeSuffix("_something")

proc composeString(
              some_string: string
              ): string = 
  for i in some_string.items:
    result.add ":" & $i
    # derived from times, line 1744 (formatPattern):
    #    result.add h & ":" & m

suite "Dings":
  test " .. 1":
    discard getShortName(name = "name_something")
  test " .. 2":
    discard composeString("something") 
    discard getShortName(name = "name_something")

Output

[Suite] Dings
  [OK]  .. 1
Traceback (most recent call last)
…\ut_label.nim(22) ut_label
…\ut_label.nim(14) composeString
…\.choosenim\toolchains\nim-1.4.2\lib\system\alloc.nim(958) alloc0
…\.choosenim\toolchains\nim-1.4.2\lib\system\alloc.nim(955) alloc
…\.choosenim\toolchains\nim-1.4.2\lib\system\alloc.nim(787) rawAlloc
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

Expected Output

... produced by executing nim c -r a_label.nim ...

[Suite] Dings
  [OK]  .. 1
  [OK]  .. 2

Comments:

• no exceptions raised if procs are executed outside the test suite
• no exceptions raised if the first test is equal to the second (including the composeString)
• no exceptions raised if the second test is equal to the first (excluding the composeString)

[timotheecour]

much better thanks! can't reproduce on osx so maybe it's windows specific

nim r --gc:arc main
[Suite] Dings
  [OK]  .. 1
  [OK]  .. 2

ditto with c -r, ditto with devel 1.5.1 9ef7c01 or 1.4.2

next steps:

• trying on earlier versions to see if it's a regression or if it has always been a bug
• further minimizing, ideally down to zero imports

(not on windows, sorry)

[SFR0815]

We will run on Linux. If not reproducible we will have to investigate further (as original issue showed up on Linux as well).

[SFR0815]

On windows outcome is the same for 1.4.2 (see above), 1.5.1 (most recent) and 1.2.6

[SFR0815]

Example (zero imports)

File "a_label.nim":

template doThis(body) =
  try:
    body
  except:
    discard
  body
 
# Task 1: 
doThis:
  # Task 1_a: 
  var test_string_a = "name_something"
  echo test_string_a.len()
  let new_len_a = test_string_a.len - "_something".len()
  test_string_a.setLen new_len_a
  
  echo "First tasks completed."

# Task 2: 
doThis:
  # Task 2_a 
  var test_string: string
  let some_string = "something"            
  for i in some_string.items:
    test_string.add $i
  
  # Task 2_b
  var test_string_b = "name_something"
  let new_len_b = test_string_b.len - "_something".len()
  test_string_b.setLen new_len_b
  
  echo "Second tasks completed."

Output

First tasks completed.
First tasks completed.
Second tasks completed.
Traceback (most recent call last)
...\ut_label.nim(24) a_label
...\.choosenim\toolchains\nim-#devel\lib\system\alloc.nim(958) alloc0
...\.choosenim\toolchains\nim-#devel\lib\system\alloc.nim(955) alloc
...\.choosenim\toolchains\nim-#devel\lib\system\alloc.nim(787) rawAlloc
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

Observations

The code with the following changes as follows and running with nim c -r --gc:arc a_label.nim does NOT throw an exception:

1. Removing the try/except from doThis
2. Removing Task 1
3. Removing Task 2_b from Task 2
4. Changing the value of test_string_a/b to "e_something" (strings with length < 12 seem to work)
5. Changing test_string.add $i to test_string.add i

nim c -r a_label.nim works without any issue.

[LucasUllon]

Hi @timotheecour , testing the a_label code on Linux I get the same output error, so the error is not only on windows.

OUTPUT

First tasks completed.
First tasks completed.
Second tasks completed.
Traceback (most recent call last)
/home/lucas/Desktop/valgrind test/a_label.nim(24) a_label
/home/lucas/.choosenim/toolchains/nim-1.4.0/lib/system/alloc.nim(976) realloc
/home/lucas/.choosenim/toolchains/nim-1.4.0/lib/system/alloc.nim(955) alloc
/home/lucas/.choosenim/toolchains/nim-1.4.0/lib/system/alloc.nim(787) rawAlloc
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

[Araq]

Almost have a fix ready...

[SFR0815]

Great! Works :-)

Thanks for your help!

Gesegnetes Weihnachtsfest aus Florida in die Heimat!

Regards
Stephan

[Araq]

Danke, gleichfalls!