[v3, build] Clear hardware capabilities on libstdc++.so with Sun as

[Paolo Bonzini]

Il 12/09/2012 11:26, Rainer Orth ha scritto:
> Since the use of rdrand was introduced in src/c++11/random.cc, all
> execution tests involving libstdc++.so.6 fail on Solaris 10 and 11/x86
> with a sufficiently recent native assembler that supports rdrand: either
> Solaris 10/x86 patch 119961-11 or Solaris 11.1 builds (haven't checked
> which one).  The problem is that as tags src/c++11/random.o as needing
> RDRAND support:
> 
> % file random.o
> random.o:       ELF 32-bit LSB relocatable 80386 Version 1 [CMOV RDRAND]
> 
> which is propagated to libstdc++.so.6 and causes the runtime linker to
> fail the execution if the hardware doesn't support that hardware
> capability, although rdrand is executed only if the cpuid indicates the
> support is present.
> 
> The usual solution so far has been to clear the hardware capability
> using a linker map (as in libitm, cf. libitm/clearcap.map).
> Unfortunately, this doesn't work here: as can be seen with elfdump,
> RDRAND is set in a second mask (CA_SUNW_HW_2) since all bits in
> CA_SUNW_HW_1 are already used:
> 
> % elfdump -H random.o
> 
> Capabilities Section:  .SUNW_cap
> 
>  Object Capabilities:
>      index  tag               value
>        [0]  CA_SUNW_HW_1     0x20  [ CMOV ]
>        [1]  CA_SUNW_HW_2     0x1  [ RDRAND ]
> 
> The old (v1) linker map syntax has no support for clearing that
> bit/mask, and while the v2 map syntax does, we cannot universally assume
> it's present on Solaris 10: while recent linker patches include it,
> older ones don't and ld and as can be updated independently.
> 
> So I've settled for a different solution instead: Sun assemblers with
> hardware capability support also have a -nH switch to suppress their
> generation, thus I'm testing for that and use it if possible.
> 
> This is exactly what the following patch does.
> 
> Bootstrapped without regressions on i386-pc-solaris2.1[01] with affected
> versions of Sun as and gas 2.22.  Results with gas are unchanged, with
> Sun as all failures are gone.  x86_64-unknown-linux-gnu bootstrap is
> running to make sure nothing breaks there.
> 
> Ok for mainline if that passes?
> 
> 	Rainer
> 
> 
> 2012-09-11  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
> 
> 	* acinclude.m4 (GLIBCXX_CHECK_ASSEMBLER_HWCAP): Define.
> 	* configure.ac: Call GLIBCXX_CHECK_ASSEMBLER_HWCAP.
> 	* fragment.am (CONFIG_CXXFLAGS): Add $(HWCAP_FLAGS).
> 	* configure: Regenerate.
> 	* Makefile.in: Regenerate.
> 	* doc/Makefile.in: Regenerate.
> 	* include/Makefile.in: Regenerate.
> 	* libsupc++/Makefile.in: Regenerate.
> 	* po/Makefile.in: Regenerate.
> 	* python/Makefile.in: Regenerate.
> 	* src/Makefile.in: Regenerate.
> 	* src/c++11/Makefile.in: Regenerate.
> 	* src/c++98/Makefile.in: Regenerate.
> 	* testsuite/Makefile.in: Regenerate.
> 
> 
> 
> 

Ok.

Paolo