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Re: TLS question
On Thu, 2012-03-22 at 19:13 -0400, Ian Lance Taylor wrote:
> Alireza Moshtaghi <firstname.lastname@example.org> writes:
> > STT_TLS is not set for my extern __thread symbol.
> > and my linker ends up emitting:
> > TLS definition in /tmp/cccF5k6P.o section .tbss mismatches non-TLS
> > reference in /tmp/ccMzRAeS.o
> > What is responsible for setting this flag? the compiler? or it is set
> > while the elf is being read? I'm sure I have failed to implement
> > something in my port.
> (Please don't top-post. Thanks.)
> The STT_TLS symbol type is in the symbol table in the .o file--you can
> see it using readelf -s. Normally the assembler, which generates the .o
> file, is responsible for setting this symbol type when it sees a
> TLS-specific relocation applied to the symbol.
> If you are using gas look for S_SET_THREAD_LOCAL.
Thank you Ian,
That did it.
Appreciate your help
> > On Thu, 2012-03-22 at 14:53 -0400, Ian Lance Taylor wrote:
> >> Alireza Moshtaghi <email@example.com> writes:
> >> > An extern variable is defined as an UND symbol in the elf file, however,
> >> > when it is classified with __thread, the linker needs to match it up
> >> > with the correct definition from another object file.
> >> > The way that I have implemented TLS support in my port of binutils, the
> >> > linker complains that the extern symbol is not TLS and it can not link
> >> > it to the definition from the other object file.
> >> >
> >> > The only thing that I can think of is to teach ld to look at the
> >> > relocation for that symbol and if it is a TLS relocation, it should be
> >> > able to match the two, but I don't know how to teach ld to do so.
> >> >
> >> > Question is: where in the linker I must modify?
> >> An extern __thread variable should be SHN_UNDEF, STB_GLOBAL, STT_TLS.
> >> In other words, you don't have to look at relocations, you just have to
> >> look at the symbol type.
> >> Ian