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mecej4
Joined: 31 Oct 2006
Posts: 1886
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 Posted: Wed Jan 20, 2016 3:53 pm Post subject: Bug with NAMELIST in contained procedure |
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When a namelist is declared in the main program or an external subroutine/function, the namelist is treated properly. However, when the namelist is declared, its members defined and the namelist printed in an internal procedure, the compiler outputs buggy code. Here is a reproducer:
| Code: |
program buggy
implicit none
call sub()
contains
subroutine sub()
integer i1,i2
namelist /nml/i1,i2
i1=23
i2=32
write(*,nml=nml)
return
end subroutine
end program
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An access violation occurs at location program base+0030H. The exp-list obscures the bug by displaying only the symbol 'NML':
| Code: |
00000000(3/1/1) push ebp
00000001(4/1/1) mov ebp,esp
00000003(5/1/1) push ebx
00000004(6/1/1) push esi
00000005(7/1/1) push edi
00000006(8/1/1) push eax
00000007(9/1/1) lea ecx,2
0000000d(10/1/1) push ecx
0000000e(11/1/1) lea esi,[ebp+8] ; Get command line arguments
00000011(12/1/1) push esi
00000012(13/1/1) call __FTN95INIT1_
00000017(14/1/1) add esp,=8
0000001a(15/1/1) sub esp,=16 ; Adjusted later if temporaries allocated
00000020(16/1/1) sub esp,=36 ; Grab space for NAMELIST block
00000023(17/1/1) mov edi,esp
00000025(18/1/1) lea esi,(/2,Z'4c4d4e04',Z'3149030e',1211906,1065,Z'030e0000',Z'03023249',Z'0451c389',0/)
0000002b(19/1/1) mov ecx,=9
00000030(20/1/1) mov NML,edi ; <<=== BUG HERE!
00000033(21/1/1) rep
00000034(22/1/1) movs
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Dumping the OBJ file with the MS Dumpbin utility gives:
| Code: |
_BUGGY:
00000000: 55 push ebp
00000001: 89 E5 mov ebp,esp
00000003: 53 push ebx
00000004: 56 push esi
00000005: 57 push edi
00000006: 50 push eax
00000007: 8D 0D 00 00 00 00 lea ecx,[_BUGGY]; linker will provide address
0000000D: 51 push ecx
0000000E: 8D 75 08 lea esi,[ebp+8]
00000011: 56 push esi
00000012: E8 00 00 00 00 call 00000017; linker will provide address
00000017: 83 C4 08 add esp,8
0000001A: 81 EC 10 00 00 00 sub esp,10h
00000020: 83 EC 24 sub esp,24h
00000023: 89 E7 mov edi,esp
00000025: 8D 35 04 00 00 00 lea esi,ds:[4]
0000002B: B9 09 00 00 00 mov ecx,9
00000030: 89 7B F0 mov dword ptr [ebx-10h],edi; <<== BUG HERE!
00000033: F3 A5 rep movs dword ptr [edi],dword ptr [esi]
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At offset 0030, the contents of register EBX are undefined; this is the first instruction where the register is used at all in the program, not counting the PUSH at the main program entry. Secondly, is it not a bit odd that the namelist, which is local to the internal subroutine, is referred to in the caller?
Last edited by mecej4 on Wed Jan 20, 2016 4:06 pm; edited 1 time in total |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 7924
Location: Salford, UK
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| Posted: Wed Jan 20, 2016 4:05 pm Post subject: |
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Thank you. I have logged this for investigation.
It runs OK with 64 bit FTN95 so that's really encouraging. |
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John-Silver
Joined: 30 Jul 2013
Posts: 1520
Location: Aerospace Valley
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| Posted: Mon Jan 25, 2016 10:15 am Post subject: |
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just an observation, is it a good idea to name the NAMELIST nml when the keyword is NML/nml ???
doesn't affect the problem which persists but a question of good coding practice I'd have thought.
Come to think of it, shouldn't it be flagged via the compiler, at least as a Warning ?
Secondly, congratulations on FTN95 64bit having been conceived to be the first compiler in the world with the foresight to predict and solve bugs !!! 
Dan will be pleased , LOL, all that devilry obliterated in an instant ! |
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mecej4
Joined: 31 Oct 2006
Posts: 1886
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| Posted: Tue Jan 26, 2016 2:29 am Post subject: Re: |
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| John-Silver wrote: | just an observation, is it a good idea to name the NAMELIST nml when the keyword is NML/nml ??? doesn't affect the problem which persists but a question of good coding practice I'd have thought.
Come to think of it, shouldn't it be flagged via the compiler, at least as a Warning ?
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Among programming languages, Fortran is the long-suffering burro -- see the concluding paragraph of https://www.computer.org/csdl/proceedings/afips/1982/5089/00/50890817.pdf . Fortran has no reserved words.
Consider this Fortran-90 quine: http://wwwep.stewartsplace.org.uk/quines/f90.html . If you rename variables and/or reformat the source code to make it comely in your view, it will probably be neither a quine nor equine. |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 7924
Location: Salford, UK
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| Posted: Wed Jun 08, 2016 7:44 am Post subject: |
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| This has now been fixed for the next release. |
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