[dev.power64] code review 124900043: runtime: ignore rt_sigaction error if it's for SIGRTMAX.

runtime: ignore rt_sigaction error if it's for SIGRTMAX.
Workaround a qemu linux user space emulation bug.
ref: http://git.qemu.org/?p=qemu.git;a=blob;f=linux-user/signal.c;h=1141054be2170128d6f7a340b41484b49a255936;hb=HEAD#l82

[minux, 2014-08-08 07:53:25]

Hello rsc@golang.org, iant@golang.org (cc: golang-codereviews@googlegroups.com),

I'd like you to review this change to the dev.power64 branch of
https://code.google.com/p/go

[minux, 2014-08-08 07:59:21]

This is for discussion, I'm not sure if it's acceptable.
(We can also only skip the error if it's EINVAL, but i think if
sizeof(sa.sa_mask) is
wrong, the kernel will also return EINVAL..)

After this change, Go code could run successfully on qemu-i386 and
qemu-ppc64
qemu-ppc64le is still buggy (i think it doesn't get the ABI right, becuase
it still seems
to expect a function descriptor at ELF entry point).

qemu-x86_64 still couldn't handle our binaries.
$ qemu-x86_64 ../bin/gofmt
setup_rt_frame: not implemented
qemu: uncaught target signal 11 (Segmentation fault) - core dumped
Segmentation fault

I haven't had time to try on arm, but initial result seems to indicate
qemu-arm is
capable of running our binary.

[rsc, 2014-08-08 12:59:57]

LGTM

https://codereview.appspot.com/124900043/diff/20001/src/pkg/runtime/os_linux.c
File src/pkg/runtime/os_linux.c (right):

https://codereview.appspot.com/124900043/diff/20001/src/pkg/runtime/os_linux....
src/pkg/runtime/os_linux.c:315: // We ignored the error if it's 64 or SIGRTMAX
because qemu-user contains
shorten comment

// Qemu rejects rt_sigaction of SIGRTMAX (64).

[minux, 2014-08-12 03:32:37]

*** Submitted as https://code.google.com/p/go/source/detail?r=a64952e4b71b ***

[dev.power64] runtime: ignore rt_sigaction error if it's for SIGRTMAX.
Workaround a qemu linux user space emulation bug.
ref:
http://git.qemu.org/?p=qemu.git;a=blob;f=linux-user/signal.c;h=1141054be21701...

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/124900043