Re: [prelink-cross][PATCH] Always create a conflict for R_ARM_TLS_DESC relocs

[Mark Hatle <mark.hatle@windriver.com>]

Thanks for the patch, I'll get it integrated later today.

(What a nasty problem for such a simple fix.)

--Mark

On 7/22/14, 9:50 AM, Maciej W. Rozycki wrote:
> Hi,
>
>   This is a bit obscure.  In my testing, for the purpose of upstreaming, of
> the glibc change to support ARM TLS descriptors in prelinked binaries (cf
> upstream BZ #17078, https://sourceware.org/bugzilla/show_bug.cgi?id=17078)
> I have come across a problem where all programs prelinked against glibc
> binaries using ARM TLS descriptors themselves segfaulted in the normal
> exit path, where libc.so's own TLS destructors are called.  I have tracked
> it down to the GOT entry (pointed to by the DT_TLSDESC_GOT dynamic tag)
> meant to point to the lazy TLS descriptor resolver (pointed to by the
> DT_TLSDESC_PLT dynamic tag) being left uninitialised and therefore NULL.
> An attempt to call that resolver caused therefore a segfault.
>
>   The cause of this lack of initialisation turned out to be an omission in
> the original fix (dated 2011-04-13 in ChangeLog.cross), that didn't ensure
> that a conflict entry is created even for these R_ARM_TLS_DESC relocations
> that refer to a local symbol.  Somehow it didn't trigger in testing back
> when implemented, perhaps glibc didn't require or access the missing entry
> in code handling TLS destructors then.  Such an entry is needed, because
> for prelinked binaries the DT_TLSDESC_GOT GOT entry is only initialised by
> the dynamic linker when a conflict is resolved.  The change below enforces
> this conflict entry creation.
>
>   This fix removes 33 failures in prelink testing with glibc built using
> ARM TLS descriptors, that is with the `-mtls-dialect=gnu2' GCC option in
> effect (that is not the default unless explicitly requested at GCC build
> time):
>
> FAIL -> PASS: default/prelink.sum:cxx1.sh
> FAIL -> PASS: default/prelink.sum:cxx2.sh
> FAIL -> PASS: default/prelink.sum:cxx3.sh
> FAIL -> PASS: default/prelink.sum:layout1.sh
> FAIL -> PASS: default/prelink.sum:layout2.sh
> FAIL -> PASS: default/prelink.sum:reloc1.sh
> FAIL -> PASS: default/prelink.sum:reloc10.sh
> FAIL -> PASS: default/prelink.sum:reloc11.sh
> FAIL -> PASS: default/prelink.sum:reloc2.sh
> FAIL -> PASS: default/prelink.sum:reloc3.sh
> FAIL -> PASS: default/prelink.sum:reloc4.sh
> FAIL -> PASS: default/prelink.sum:reloc5.sh
> FAIL -> PASS: default/prelink.sum:reloc6.sh
> FAIL -> PASS: default/prelink.sum:reloc7.sh
> FAIL -> PASS: default/prelink.sum:reloc8.sh
> FAIL -> PASS: default/prelink.sum:reloc9.sh
> FAIL -> PASS: default/prelink.sum:shuffle1.sh
> FAIL -> PASS: default/prelink.sum:shuffle2.sh
> FAIL -> PASS: default/prelink.sum:shuffle3.sh
> FAIL -> PASS: default/prelink.sum:shuffle4.sh
> FAIL -> PASS: default/prelink.sum:shuffle5.sh
> FAIL -> PASS: default/prelink.sum:shuffle6.sh
> FAIL -> PASS: default/prelink.sum:shuffle7.sh
> FAIL -> PASS: default/prelink.sum:shuffle8.sh
> FAIL -> PASS: default/prelink.sum:shuffle9.sh
> FAIL -> PASS: default/prelink.sum:tls1.sh
> FAIL -> PASS: default/prelink.sum:tls2.sh
> FAIL -> PASS: default/prelink.sum:tls3.sh
> FAIL -> PASS: default/prelink.sum:tls4.sh
> FAIL -> PASS: default/prelink.sum:tls5.sh
> FAIL -> PASS: default/prelink.sum:tls6.sh
> FAIL -> PASS: default/prelink.sum:tls7.sh
> FAIL -> PASS: default/prelink.sum:undo1.sh
>
>   Please apply.
>
> 2014-07-22  Maciej W. Rozycki  <macro@codesourcery.com>
>
> 	* src/arch-arm.c (arm_prelink_conflict_rel): Always create a
> 	conflict for R_ARM_TLS_DESC relocs.
> 	(arm_prelink_conflict_rela): Likewise.
>
>    Maciej
>
> prelink-arm-tlsdesc-conflict-always.diff
> Index: trunk/src/arch-arm.c
> ===================================================================
> --- trunk.orig/src/arch-arm.c	2014-07-17 23:26:08.000000000 +0100
> +++ trunk/src/arch-arm.c	2014-07-18 04:18:53.790564615 +0100
> @@ -416,7 +416,9 @@ arm_prelink_conflict_rel (DSO *dso, stru
>   	case R_ARM_TLS_DTPMOD32:
>   	case R_ARM_TLS_TPOFF32:
>   	  break;
> -
> +	/* Likewise TLS_DESC.  */
> +	case R_ARM_TLS_DESC:
> +	  break;
>   	default:
>   	  return 0;
>   	}
> @@ -526,7 +528,9 @@ arm_prelink_conflict_rela (DSO *dso, str
>   	case R_ARM_TLS_DTPMOD32:
>   	case R_ARM_TLS_TPOFF32:
>   	  break;
> -
> +	/* Likewise TLS_DESC.  */
> +	case R_ARM_TLS_DESC:
> +	  break;
>   	default:
>   	  return 0;
>   	}
>