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Hi, crossposted to gdb+glibc as the patches closely correlate: currently gdb/glibc cannot access TLS of debugged processes if compiled without libpthread (nonthreaded). Command line `print errno' produces one of: Cannot find thread-local variables on this target Cannot access memory at address 0x8 [ gdb-20060908-tls-0.patch: gdb.threads/tls-print.exp ] It also affects stepping over longjmp() as gdb calculates target address which is PTR_MANGLE()d through TLS-based `pointer_guard' magic, as `next' will now: Cannot insert breakpoint -12. Error accessing memory address 0xb9227d3b: Input/output error. [ gdb-20060908-tls-0.patch: gdb.threads/tls-longjmp.exp ] I would like to get approval of this design acceptance to finish the details. glibc part: * Provide some access to the `tcbhead_t.pointer_guard' field for gdb. Currently implemented by `td_thr_getxregs' providing only `pointer_guard'. New non-Solaris `td_thr_*' function could be provided instead. * All the `libthread_db' functions accessing inferior's `_thread_db*' symbols of `libpthread' fallback to the new `_local_db*' symbols in `libthread_db' itself. `libthread_db'<=>`libpthread' versions must match anyway. I admit I do not know how may `libthread_db' and `libpthread' as there is already required in `td_ta_new' their versions match. Anyway it should be enough for 99% of cases - as the fallback option. gdb part: * `longjmp' decoder attempts to use `td_thr_getxregs', otherwise fallbacks to get the TLS base by `ps_get_thread_area' and the offset value `offsetof (tcbhead_t, pointer_guard)' from debuginfo, otherwise fallbacks to internal constant offset. * `SEC_THREAD_LOCAL' symbols are processed as a new expression data type. * TLS variables access uses legacy `thread_db_get_thread_local_address' as it depends on the `_local_db*' fallback implementation for nonthreaded processes missing `libthread_db' with the legacy `_thread_db*' symbols. `longjmp' decoder can cope without glibc support by using debuginfo instead. I would rather like to drop this workaround and rely on the glibc support. TLS access needs the attached glibc patch for the nonthreaded processes. I could provide gdb decoding without glibc support but I do not like it. It works now only on i386, x86_64 to be debugged if it is accepted this way. Patches still contain several FIXMEs; their fixes should not change the design. glibc part should be arch-dependent, it will now fail to compile on arches without existing `pointer_guard'. Behavior changes depending on: * Application linked with libpthread or without libpthread. * glibc original/patched by this TLS extension. * -ggdb3 (overriding the TLS `errno' resolving just by the macro text). * Debuginfo availability for libpthread (for `longjmp'). Unfortunately the system changes cannot be tested just by the gdb testsuite. Thanks, Jan
Attachment:
glibc-20060828T1903-26-local_db+xregs-0.patch
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Attachment:
gdb-20060908-tls-0.patch
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