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https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=185337
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currently for trivia nonthreaded helloworld with no debug info up to -ggdb2 you
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will get:
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(gdb) p errno
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[some error]
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* with -ggdb2 and less "errno" in fact does not exist anywhere as it was
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compiled to "(*__errno_location ())" and the macro definition is not present.
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Unfortunately gdb will find the TLS symbol and it will try to access it but
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as the program has been compiled without -lpthread the TLS base register
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(%gs on i386) is not setup and it will result in:
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Cannot access memory at address 0x8
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Attached suggestion patch how to deal with the most common "errno" symbol
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for the most common under-ggdb3 compiled programs.
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2006-08-25 Jan Kratochvil <jan.kratochvil@redhat.com>
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* target.c (target_translate_tls_address): Provided warnings for TLS
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`errno' on non-TLS targets.
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Index: gdb-6.6/gdb/target.c
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===================================================================
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--- gdb-6.6.orig/gdb/target.c 2007-01-17 01:25:31.000000000 +0100
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+++ gdb-6.6/gdb/target.c 2007-01-20 06:31:36.000000000 +0100
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@@ -898,7 +898,18 @@
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/* It wouldn't be wrong here to try a gdbarch method, too; finding
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TLS is an ABI-specific thing. But we don't do that yet. */
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else
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- error (_("Cannot find thread-local variables on this target"));
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+ {
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+ struct minimal_symbol *msymbol;
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+
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+ msymbol = lookup_minimal_symbol ("errno", NULL, NULL);
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+ if (msymbol != NULL
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+ && SYMBOL_VALUE_ADDRESS (msymbol) == offset
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+ && SYMBOL_BFD_SECTION (msymbol)->owner == objfile->obfd)
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+ error (_("TLS symbol `errno' not resolved for non-TLS program."
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+ " You should use symbol \"(*__errno_location ())\" or"
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+ " compile the program with `gcc -ggdb3' or `gcc -pthread'."));
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+ error (_("Cannot find thread-local variables on this target"));
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+ }
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return addr;
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}
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