[llvm] r227411 - [LPM] Clean up the use of TLS in pretty stack trace and disable it

[Eric Christopher]

*nod* You might want to try top of tree.

-eric

On Thu Jan 29 2015 at 11:44:55 AM Kristof Beyls <kristof.beyls at arm.com>
wrote:

> Hi Eric,
>
>
>
> I’ve experimented a bit with a **very** simple program using a TLS
> variable.
>
> It seems to me that in binutils 2.25, ld.bfd supports non-PIC compiled
> code and ld.gold support PIC-compiled code.
> But neither supports both PIC and non-PIC compiled TLS variables.
>
> For details of my experiments, see below.
>
>
>
> $ cat t3.cpp
>
> static volatile thread_local int tls_i;
>
>
>
> int main() {
>
>   tls_i = 4;
>
>   return tls_i;
>
> }
>
> # Works with g++ 4.9.1:
>
> $ g++ -O3 -std=c++11 -o t3_g++-4.9.1_O3 t3.cpp
>
> # breaks with clang++-3.5 in combination with gold 2.25:
>
> $ clang++-3.5 -O3 -std=c++11 -o t3_clang++-3.5_O3 t3.cpp -Wl,-v
>
> GNU gold (GNU Binutils for Debian 2.25) 1.11
>
> /usr/bin/ld: error: /tmp/t3-4c39c0.o: unsupported reloc 545 against local
> symbol
>
> /usr/bin/ld: error: /tmp/t3-4c39c0.o: unsupported reloc 548 against local
> symbol
>
> /tmp/t3-4c39c0.o:t3.cpp:function main: error: cannot relocate invalid
> reloc 545 in object file
>
> /tmp/t3-4c39c0.o:t3.cpp:function main: error: cannot relocate invalid
> reloc 548 in object file
>
> clang: error: linker command failed with exit code 1 (use -v to see
> invocation)
>
> # works with clang++-3.5 and ld.bfd 2.25:
>
> $ clang++-3.5 -O3 -std=c++11 -o t3_clang++-3.5_O3 t3.cpp -Wl,-v
> -fuse-ld=bfd
>
> GNU ld (GNU Binutils for Debian) 2.25
>
> llvm-test at llvm-farm-juno-5:~/kristof$ ./t3_clang++-3.5_O3; echo $?
>
> 4
>
> # SUMMARY: so far, gold doesn’t support some TLS relocations that clang
> produces.
>
> # Try another example to show the problem with ld.bfd, on relocation
> 0x20c=524=R_AARCH64_TLSLD_MOVW_DTPREL_G1:
>
> clang++-3.5 -fPIC -O3 -std=c++11 -o t3_clang++-3.5_O3 t3.cpp -Wl,-v
> -fuse-ld=bfd
>
> GNU ld (GNU Binutils for Debian) 2.25
>
> /usr/bin/ld.bfd: /tmp/t3-3b0353.o: unrecognized relocation (0x20c) in
> section `.text'
>
> /usr/bin/ld.bfd: final link failed: Bad value
>
> clang: error: linker command failed with exit code 1 (use -v to see
> invocation)
>
> llvm-test at llvm-farm-juno-5:~/kristof$ clang++-3.5 -fPIC -O3 -std=c++11 -o
> t3_clang++-3.5_O3 t3.cpp -Wl,-v
>
> GNU gold (GNU Binutils for Debian 2.25) 1.11
>
>
>
>
>
> *From:* Eric Christopher [mailto:echristo at gmail.com]
> *Sent:* 29 January 2015 19:38
> *To:* Kristof Beyls; Chandler Carruth; Hans Wennborg; jingyu at google.com
>
>
> *Cc:* Commit Messages and Patches for LLVM
> *Subject:* Re: [llvm] r227411 - [LPM] Clean up the use of TLS in pretty
> stack trace and disable it
>
>
>
> Hi Kristof,
>
>
>
> I know Jing (on this email) was working on gold tls relocations when I
> noticed this a while back. I'm pretty sure she implemented them (at least I
> can link now), but I'm not sure how well it's working. Can you confirm or
> elaborate more?
>
>
>
> -eric
>
>
>
> On Thu Jan 29 2015 at 11:25:23 AM Kristof Beyls <kristof.beyls at arm.com>
> wrote:
>
> For AArch64, clang produces relocations for TLS variables that ld.bfd or
> ld.gold can’t handle.
>
> It seems that gcc, ld and gas only support the “small memory model 16Mib
> TLS address model”,
> and AFAIK, it may take a while for these to grow support for other address
> models.
>
>
>
> I haven’t had time to come fully up to speed on this, but at the moment,
> the only workable
> solution I can think of is to:
>
> ·         Not use thread_local variables in LLVM for the 3.6 release on
> AArch64, so that clang 3.6
> can bootstrap itself on AArch64-linux.
>
> ·         On trunk, let clang targeting AArch64-ELF systems only produce
> the relocations that ld supports.
> At first sight that seems possible, but I’m not sure.
>
>
>
> Does anyone have a better set of suggestions than the above?
>
>
>
> Thanks,
>
>
>
> Kristof
>
>
>
> *From:* llvm-commits-bounces at cs.uiuc.edu [mailto:
> llvm-commits-bounces at cs.uiuc.edu] *On Behalf Of *Chandler Carruth
> *Sent:* 29 January 2015 18:59
> *To:* Hans Wennborg
> *Cc:* Commit Messages and Patches for LLVM
> *Subject:* Re: [llvm] r227411 - [LPM] Clean up the use of TLS in pretty
> stack trace and disable it
>
>
>
> I'm still waiting for some of the dust to settle with ppc and arm. I'll
> have a list before long and can help merge.
>
> On Jan 29, 2015 9:50 AM, "Hans Wennborg" <hans at chromium.org> wrote:
>
> On Wed, Jan 28, 2015 at 5:23 PM, Chandler Carruth <chandlerc at gmail.com>
> wrote:
> > Author: chandlerc
> > Date: Wed Jan 28 19:23:04 2015
> > New Revision: 227411
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=227411&view=rev
> > Log:
> > [LPM] Clean up the use of TLS in pretty stack trace and disable it
> > entirely when threads are not enabled. This should allow anyone who
> > needs to bootstrap or cope with a host loader without TLS support to
> > limp along without threading support.
>
> I assume we want this (and r227412) for the 3.6 branch. Any others?
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