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| -rw-r--r-- | src/libthread/README.Linux | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/src/libthread/README.Linux b/src/libthread/README.Linux new file mode 100644 index 00000000..cc193eeb --- /dev/null +++ b/src/libthread/README.Linux @@ -0,0 +1,37 @@ +Thread support on Linux is confused by the recent thread local storage (TLS) +support that has been put into the ELF tool chain. The TLS libraries are +installed in /lib/tls on most Linux systems. + +We provide two different implementations of the os-dependent parts +of libthread for Linux. The first is intended for use on Linux 2.4 and earlier +kernels, which do not support TLS. It is in Linux.c and Linuxasm.c and +does not use the pthread interface. The second is intended for Linux 2.6 +and later kernels, which do support TLS. It is in pthread.c and uses the +standard pthread interface. It expects to be linked against the TLS-aware +thread library aka NPTL. + +If you use Linux.c and Linuxasm.c with TLS libraries, they do not +set up the TLS properly so you will get incorrect programs. +For example, there will only be one errno among all the procs +in your program instead of one per proc. The pthread NPTL +implementation is needed to use the TLS libraries properly. + +If you use pthread.c without TLS libraries (i.e., with the old Linux +pthread library known as LinuxThreads), then you will also get +incorrect programs, although more obviously so. The LinuxThreads +library assumes it can look at the stack pointer to distinguish between +threads, but libthread does its own stack management, breaking this +assumption. If you run a pthread-compiled program with the +LinuxThreads library, LinuxThreads itself will cause a segmentation +fault in __pthread_getspecific() the first time it is called from a +non-standard stack. + +So, it is important that you compile binaries that match your +system's choice of TLS vs. not-TLS libraries. The hard part is figuring +out which your system has chosen. Plan9port looks at the kernel +version you are running and assumes that on kernels that support +TLS (2.6+) you will be using TLS. + +Apparently Gentoo and maybe other distributions do not follow this rule. +They use non-TLS libraries even on kernels that can support TLS. + |