Fork#39174: Invalid code generated for extern thead_local variables
Open Date: 2019-04-29 19:23
Last Update: 2019-04-29 19:23
URL for this Ticket:
https://osdn.net//projects/mingw/ticket/39174
RSS feed for this Ticket:
https://osdn.net/ticket/ticket_rss.php?group_id=3917&tid=39174
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Last Changes/Comment on this Ticket:
2019-04-29 19:23 Updated by: vagran
* New Ticket "Invalid code generated for extern thead_local variables" created
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Ticket Status:
Reporter: vagran
Owner: (None)
Type: Issues
Status: Open
Priority: 5 - Medium
MileStone: (None)
Component: (None)
Severity: 5 - Medium
Resolution: None
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Ticket details:
Compiler produces some strange code when using C++11 global thread local
variables. The produced binary also permamently crashes when built in some
circumstances. The problem is visible on all optimization levels above -O0, the
binary compiled with -O0 looks good.
I use MSYS2 build environment with gcc 8.3.0 installed. Extract the attached
minimal example and run the following commands:
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make
Then inspect the produced code with the GDB:
gdb sample.exe
(gdb) disas main
Dump of assembler code for function main():
0x0000000000402d20 <+0>: sub $0x28,%rsp
0x0000000000402d24 <+4>: callq 0x401610 <__main>
0x0000000000402d29 <+9>: lea -0x402d30(%rip),%rax # 0x0
0x0000000000402d30 <+16>: test %rax,%rax
0x0000000000402d33 <+19>: je 0x402d3a <main()+26>
0x0000000000402d35 <+21>: callq 0x0
0x0000000000402d3a <+26>: mov 0x160f(%rip),%rcx # 0x404350 <.refptr.__emutls_v.tl>
0x0000000000402d41 <+33>: callq 0x402af0 <__emutls_get_address>
0x0000000000402d46 <+38>: movl $0x2a,(%rax)
0x0000000000402d4c <+44>: xor %eax,%eax
0x0000000000402d4e <+46>: add $0x28,%rsp
0x0000000000402d52 <+50>: retq
The strange thing is instruction at <+9> "lea -0x703813bb(%rip),%rax" which
calculates some address, the result is tested against zero at <+16> and call to
this address is executed at <+21> in case it is non-zero. In this particular
example the result is zero, so it does not crash. But in my case the result was
not zero and still invalid which causes a crash. Unfortunately my example is
not easy reproducible, it probably was triggered after I statically linked my
DLL with large library (ffmpeg) and the calculated address became non-zero.
Besides that even in the attached example the idea behind this strange address
manipulation is not clear and looks like some code optimization bug.
0x000000007771425d <+13>: lea -0x6f254264(%rip),%rax # 0x84c0000
0x0000000077714264 <+20>: mov %rcx,%rbx
0x0000000077714267 <+23>: mov %rdx,%rdi
0x000000007771426a <+26>: mov %r8,%rbp
0x000000007771426d <+29>: mov %r9,%r12
0x0000000077714270 <+32>: test %rax,%rax
0x0000000077714273 <+35>: je 0x7771427a <Func()+42>
0x0000000077714275 <+37>: callq 0x84c0000 // <<<<<<<< Crash here!
0x000000007771427a <+42>: mov 0x813e3f(%rip),%rcx # 0x77f280c0 <.refptr.__emutls_v._ZN4java6jniEnvE>
Compare this code with one compiled with -O0:
cmake -DCMAKE_BUILD_TYPE=Debug ..
make
(gdb) disas main
Dump of assembler code for function main():
0x0000000000401560 <+0>: push %rbp
0x0000000000401561 <+1>: mov %rsp,%rbp
0x0000000000401564 <+4>: sub $0x20,%rsp
0x0000000000401568 <+8>: callq 0x401640 <__main>
0x000000000040156d <+13>: callq 0x402d50 <_ZTW2tl> // "TLS wrapper function for tl"
0x0000000000401572 <+18>: movl $0x2a,(%rax)
0x0000000000401578 <+24>: mov $0x0,%eax
0x000000000040157d <+29>: add $0x20,%rsp
0x0000000000401581 <+33>: pop %rbp
0x0000000000401582 <+34>: retq
(gdb) disas _ZTW2tl
Dump of assembler code for function _ZTW2tl:
0x0000000000402d50 <+0>: push %rbp
0x0000000000402d51 <+1>: mov %rsp,%rbp
0x0000000000402d54 <+4>: sub $0x20,%rsp
0x0000000000402d58 <+8>: mov 0x15a1(%rip),%rax # 0x404300 <.refptr._ZTH2tl> //"TLS init function for tl"
0x0000000000402d5f <+15>: test %rax,%rax
0x0000000000402d62 <+18>: je 0x402d69 <_ZTW2tl+25>
0x0000000000402d64 <+20>: callq 0x0
0x0000000000402d69 <+25>: mov 0x15e0(%rip),%rcx # 0x404350 <.refptr.__emutls_v.tl>
0x0000000000402d70 <+32>: callq 0x402b20 <__emutls_get_address>
0x0000000000402d75 <+37>: add $0x20,%rsp
0x0000000000402d79 <+41>: pop %rbp
0x0000000000402d7a <+42>: retq
It is seen that TLS wrapper is not inlined in this case and instead of
calculating some address, some real variable read is generated at <+8> which
looks more correct. The calling address at <+20> is probably replaced with a
correct one when runtime-linked to some process context. In my case it looks
like this:
(gdb) disas _ZTWN4java6jniEnvE
Dump of assembler code for function _ZTWN4java6jniEnvE:
0x000000005c4aa790 <+0>: push %rbp
0x000000005c4aa791 <+1>: mov %rsp,%rbp
0x000000005c4aa794 <+4>: sub $0x20,%rsp
0x000000005c4aa798 <+8>: mov 0xa1cf1(%rip),%rax # 0x5c54c490 <.refptr._ZTHN4java6jniEnvE>
0x000000005c4aa79f <+15>: test %rax,%rax
0x000000005c4aa7a2 <+18>: je 0x5c4aa7a9 <_ZTWN4java6jniEnvE+25>
0x000000005c4aa7a4 <+20>: callq 0xffffffffec9a0000
0x000000005c4aa7a9 <+25>: mov 0xa1ff0(%rip),%rcx # 0x5c54c7a0 <.refptr.__emutls_v._ZN4java6jniEnvE>
0x000000005c4aa7b0 <+32>: callq 0x5c1a0268 <__emutls_get_address>
0x000000005c4aa7b5 <+37>: add $0x20,%rsp
0x000000005c4aa7b9 <+41>: pop %rbp
0x000000005c4aa7ba <+42>: retq
And it does not crash and works as expected, and crashing if compiled with -O1,
-O2 or -O3. It would be nice to know what is the idea behind the address
calculation instead of variable reading in debug build, which also
significantly changes application logic between release and debug build which
is very suspicious. For now, it looks like some optimization bug.
gcc -v
Using built-in specs.
COLLECT_GCC=C:\msys\mingw64\bin\gcc.exe
COLLECT_LTO_WRAPPER=C:/msys/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.3.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../gcc-8.3.0/configure --prefix=/mingw64 --with-local-prefix=/mingw64/local --build=x86_64-w64-mingw32 --host=x86_64-w64-mingw32 --target=x86_64-w64-mingw32 --with-native-system-header-dir=/mingw64/x86_64-w64-mingw32/include --libexecdir=/mingw64/lib --enable-bootstrap --with-arch=x86-64 --with-tune=generic --enable-languages=ada,c,lto,c++,objc,obj-c++,fortran --enable-shared --enable-static --enable-libatomic --enable-threads=posix --enable-graphite --enable-fully-dynamic-string --enable-libstdcxx-filesystem-ts=yes --enable-libstdcxx-time=yes --disable-libstdcxx-pch --disable-libstdcxx-debug --disable-isl-version-check --enable-lto --enable-libgomp --disable-multilib --enable-checking=release --disable-rpath --disable-win32-registry --disable-nls --disable-werror --disable-symvers --with-libiconv --with-system-zlib --with-gmp=/mingw64 --with-mpfr=/mingw64 --with-mpc=/mingw64 --with-isl=/mingw64 --with-pkgversion='Rev2, Built by MSYS2 project' --with-bugurl=https://sourceforge.net/projects/msys2 --with-gnu-as --with-gnu-ld
Thread model: posix
gcc version 8.3.0 (Rev2, Built by MSYS2 project)
uname -a
MSYS_NT-6.1 artyom-VM 2.11.2(0.329/5/3) 2018-11-26 09:22 x86_64 Msys
I also tried to compile the sample with clang, it failed to link:
[100%] Linking CXX executable sample.exe
/usr/bin/cmake.exe -E cmake_link_script CMakeFiles/sample.dir/link.txt --verbose=1
/mingw64/bin/clang++.exe -g -O3 -DNDEBUG -Wl,--enable-auto-import CMakeFiles/sample.dir/main.cpp.o CMakeFiles/sample.dir/tls.cpp.o -o sample.exe -Wl,--out-implib,libsample.dll.a -Wl,--major-image-version,0,--minor-image-version,0
CMakeFiles/sample.dir/tls.cpp.o:(.text+0x0): multiple definition of `TLS wrapper function for tl'
CMakeFiles/sample.dir/main.cpp.o:(.text+0x50): first defined here
clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)
$ clang++ -v
clang version 7.0.1 (tags/RELEASE_701/final)
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:\msys\mingw64\bin
--
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