pitter patter on the keyboard

If you run into this error while updating glibc:

# emerge --update gcc glibc

 * IMPORTANT: 6 news items need reading for repository 'gentoo'.
 * Use eselect news to read news items.

Calculating dependencies -[root@hd-t3672cl ~]# xm console dns2
... done!
[ebuild     U ] dev-libs/mpfr-3.0.1_p4 [2.4.1_p5]
[ebuild     U ] sys-devel/gcc-config-1.5-r2 [1.4.1]
[ebuild  N    ] virtual/os-headers-0 
[ebuild  N    ] dev-libs/mpc-0.8.2 
[ebuild  NS   ] sys-devel/gcc-4.5.3-r2 [4.3.4] USE="cxx hardened mudflap nls nptl openmp (-altivec) -bootstrap -build -doc (-fixed-point) -fortran -gcj -graphite -gtk (-libssp) -lto (-multilib) -multislot -nocxx -nopie -nossp -objc -objc++ -objc-gc -test -vanilla" 
[ebuild     U ] sys-libs/glibc-2.13-r4 [2.10.1-r1] USE="hardened*" 
[ebuild     U ] sys-devel/gcc-4.3.6-r1 [4.3.4] USE="cxx%* hardened* nptl* -fortran* (-libssp) -nossp%" 
[blocks B     ] <sys-devel/patch-2.6 ("<sys-devel/patch-2.6" is blocking sys-libs/glibc-2.13-r4)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  ('ebuild', '/', 'sys-libs/glibc-2.13-r4', 'merge') pulled in by
    >=sys-libs/glibc-2.8 required by ('ebuild', '/', 'sys-devel/gcc-4.5.3-r2', 'merge')
    >=sys-libs/glibc-2.8 required by ('ebuild', '/', 'sys-devel/gcc-4.3.6-r1', 'merge')
    glibc


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked

 * IMPORTANT: 6 news items need reading for repository 'gentoo'.
 * Use eselect news to read news items.

Update patch first and carry on:

# emerge --update patch
# emerge --update glibc gcc

When compiling glibc or gcc you may encounter:

configure: error: gcc must provide the  header
 * ERROR: sys-libs/glibc-2.12.2 failed (compile phase):
 *   failed to configure glibc
 * 
 * Call stack:
 *           ebuild.sh, line   56:  Called src_compile
 *         environment, line 3723:  Called eblit-run 'src_compile'
 *         environment, line 1175:  Called eblit-glibc-src_compile
 *   src_compile.eblit, line  217:  Called toolchain-glibc_src_compile
 *   src_compile.eblit, line  128:  Called glibc_do_configure 'nptl'
 *   src_compile.eblit, line  104:  Called die
 * The specific snippet of code:
 *      "${S}"/configure ${myconf} || die "failed to configure glibc"

This is because your currently selected GCC profile is too old.

# gcc-config -l
 [1] i686-pc-linux-gnu-3.4.6
 [2] i686-pc-linux-gnu-3.4.6-hardened
 [3] i686-pc-linux-gnu-3.4.6-hardenednopie
 [4] i686-pc-linux-gnu-3.4.6-hardenednopiessp
 [5] i686-pc-linux-gnu-3.4.6-hardenednossp
 [6] i686-pc-linux-gnu-4.1.2 *
 [7] i686-pc-linux-gnu-4.3.4

# gcc-config 7 
 * Switching native-compiler to i686-pc-linux-gnu-4.3.4 ...
>>> Regenerating /etc/ld.so.cache...

 * If you intend to use the gcc from the new profile in an already
 * running shell, please remember to do:

 *   # source /etc/profile

# source /etc/profile

Now update your gcc (if applicable) and switch to its profile repeating the steps above:

# emerge --update gcc

You may encounter the following error while compiling Cairo:

/usr/include/libiberty.h:589: error: expected declaration specifiers or '...' before numeric constant
/usr/include/libiberty.h:589: error: conflicting types for '__asprintf_chk'
/usr/include/bits/stdio2.h:135: error: previous declaration of '__asprintf_chk' was here
make[4]: *** [libcairo_trace_la-lookup-symbol.lo] Error 1
make[4]: Leaving directory `/var/tmp/portage/x11-libs/cairo-1.10.2-r1/work/cairo-1.10.2/util/cairo-trace'
make[3]: *** [all-recursive] Error 1
make[3]: Leaving directory `/var/tmp/portage/x11-libs/cairo-1.10.2-r1/work/cairo-1.10.2/util'
make[2]: *** [all] Error 2
make[2]: Leaving directory `/var/tmp/portage/x11-libs/cairo-1.10.2-r1/work/cairo-1.10.2/util'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/tmp/portage/x11-libs/cairo-1.10.2-r1/work/cairo-1.10.2'
make: *** [all] Error 2
emake failed
 * ERROR: x11-libs/cairo-1.10.2-r1 failed (compile phase):
 *   emake failed
 *
 * Call stack:
 *     ebuild.sh, line   56:  Called src_compile
 *   environment, line 3089:  Called _eapi2_src_compile
 *     ebuild.sh, line  669:  Called die
 * The specific snippet of code:
 *              emake || die "emake failed"

This error is a result of how old versions of glibc behave when compiled with SSP. Temporarily remove -fstack-protector or -PIC from your CFLAGS and update glibc:

# emerge --update glibc gcc
# emerge cairo