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ID Category Severity Reproducibility Date Submitted Last Update
0000041 [libFirm] backend minor always 2009-03-03 01:34 2017-05-08 16:14
Reporter moritz View Status public  
Assigned To
Priority normal Resolution open  
Status confirmed   Product Version 1.16.0
Summary 0000041: TLS does not work on Cygwin
Description In MinGW mode, libFirm generates invalid assembler code for testcase firm_testsuite/opt/thread.c which uses "__thread" modifiers (invalid section declaration: '.section .tbss,"awT",@nobits').
Additional Information Just removing ",@nobits" results in the GAS warning "unknown section attribute 'T'".
The generated code tries to get a TLS pointer from gs:[0] which is simply not valid on Windows.

Trying to build this testcase with gcc 3.4.4 on Cygwin results in this error messages:
opt/thread.c:5: error: thread-local storage not supported for this target
opt/thread.c:6: error: thread-local storage not supported for this target
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-  Notes
(0000061)
Matze (administrator)
2009-03-03 21:16

 so what's the correct solution, disallowing thread local storage on mingw target?
(0000066)
moritz (manager)
2009-03-04 12:26

 Looking at how Visual C compiles thread.c it uses a special .tls PE section:

PUBLIC _tls_i
PUBLIC _tls_j
_TLS SEGMENT
_tls_i DD 0aH DUP (?)
_tls_j DD 05H
_TLS ENDS
PUBLIC _test
EXTRN __tls_array:DWORD
EXTRN __tls_index:DWORD

[...]

; 9 : tls_j = i;

    mov eax, DWORD PTR __tls_index
    mov ecx, DWORD PTR fs:__tls_array
    mov edx, DWORD PTR [ecx+eax*4]
    mov eax, DWORD PTR _i$[ebp]
    mov DWORD PTR _tls_j[edx], eax

More info on this can be found at: http://www.microsoft.com/whdc/system/platform/firmware/PECOFF.mspx [^]

According to http://sourceware.org/ml/binutils/2003-10/msg00369.html [^] and http://gcc.gnu.org/ml/gcc/2006-06/msg00324.html [^] binutils already have some support for the .tls table ("Fortunately, the linker already supports setting the TLS directory entry in the PE header if a symbol named "__tls_used" exists.").
Sadly I didn't find a proper example on how an according .s file should look like. Trying

[...]
    .section .tls
.globl __tls_used
    .long 2
.globl _tls_i
    .p2align 2
_tls_i:
    .space 40
.globl _tls_j
    .p2align 2
_tls_j:
    .long 0x00000005

causes an segmentation fault in ld...
(0000067)
moritz (manager)
2009-03-04 17:11

 The definition of __tls_used was missing. I fixed the bug in ld nonetheless (http://sourceware.org/bugzilla/show_bug.cgi?id=9923). [^]
Now __tls_used must only be filled with some sensible data (IMAGE_TLS_DIRECTORY). A C example can be found here: http://sourceware.org/ml/binutils/2003-10/msg00369.html [^]
(0000288)
travm1 (reporter)
2017-04-07 05:49

 The wiki page for Cygwin has some interesting points: https://www.everipedia.com/Cygwin/ [^]
(0000293)
waldgrasgeniesser (reporter)
2017-05-08 16:14

 I don't care that you broke your elbow.

- Issue History
Date Modified Username Field Change
2009-03-03 01:34 moritz New Issue
2009-03-03 21:16 Matze Note Added: 0000061
2009-03-03 21:16 Matze Status new => confirmed
2009-03-03 21:20 Matze version => 1.16.0
2009-03-04 12:26 moritz Note Added: 0000066
2009-03-04 17:11 moritz Note Added: 0000067
2017-04-07 05:49 travm1 Note Added: 0000288
2017-05-08 16:14 waldgrasgeniesser Note Added: 0000293

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