rfc:tls

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rfc:tls [2008/08/26 14:23] – . lbarnaudrfc:tls [2008/08/26 14:28] – . lbarnaud
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 ==== Static model ==== ==== Static model ====
  
-Each block is allocated at a fixed (linker-defined) offset from an address specific to each thread. As this address can be accessed very quickly, this allows very quick access to each TLS block. For instance, on Linux/IA-32, this thread-specific-address is the Thread Control Block, whose address is stored in offset 0 of the %gs segment register.+Each block is allocated at a fixed (loader-defined) offset from an address specific to each thread. As this address can be accessed very quickly, this allows very quick access to each TLS block. For instance, on Linux/IA-32, this thread-specific-address is the Thread Control Block, whose address is stored in offset 0 of the %gs segment register.
  
 The way the static model works requires that the memory needed by each TLS variable to be allocated before program startup. This means that the static model can not be used in shared libraries loaded at runtime.  The way the static model works requires that the memory needed by each TLS variable to be allocated before program startup. This means that the static model can not be used in shared libraries loaded at runtime. 
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 Linux, Solaris, FreeBSD, Windows. Linux, Solaris, FreeBSD, Windows.
  
-Linux, Solaris and FreeBSD implementations allocate a fixed amount of surplus memory especially to allow dynamically loaded libraries to use the static model. Linux allocates 1664 bytes, FreeBSD 64 and Solaris 512. This amount of memory is always allocated in addition of the memory allocated for TLS before program startup, and is always available (this memory can be used only by dlopen()ed modules using static TLS). These behaviors are undocumented. This has been tested with a test program and verified by reading the relevant code on Linux and FreeBSD.+Linux, Solaris and FreeBSD implementations allocate a fixed amount of surplus memory especially to allow dynamically loaded libraries to use the static model. Linux allocates 1664 bytes, FreeBSD 64 and Solaris 512. This amount of memory is always allocated in addition of the memory allocated for TLS before program startup, and is always available (this memory can be used only by dlopen()ed modules using static TLS). These behaviors are undocumented (except by comments in Linux and FreeBSD loaders/linkers code). This has been tested with a test program and verified by reading the relevant code on Linux and FreeBSD.
  
 On GCC this model can be selected by using -ftls-model=initial-exec. On SunStudio: -xthreadvar=no%dynamic. For both, this model is the default one when building non-PIC code. On GCC this model can be selected by using -ftls-model=initial-exec. On SunStudio: -xthreadvar=no%dynamic. For both, this model is the default one when building non-PIC code.
rfc/tls.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1

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