Support buildin setjmp/longjmp for ARM

[winlinvip]

The ARM use glibc setjmp/longjmp, which is not available for high version ARM, for example, RespberryPi2. We must use the buildin setjmp/longjmp like the ia64/x86-64/amd64/i386, use asm to implements setjmp/longjmp.

[winlinvip]

RaspberryPi2，__GLIBC__=2, __GLIBC_MINOR__=19，the setjmp/longjmp use guarded jmpbuf, we cannot directly set the SP.

[winlinvip]

We can merge from michaeltalyansky:

1. correct SP offset in jmpbif structure to be 8
2. mangle SP on ARM before storing into jmpbuf

[winlinvip]

SRS2.0 don't check the glibc version in ossrs/srs@e775eb3, but user must use the patched ST, should not use the ST of SRS in ARM.

To build ST of SRS, read usage of ST.

[winlinvip]

xzh3836598 send a PR to support buildin setjmp/longjmp for ARM, it's another solution. #3

[winlinvip]

PI2 is ok.

[winlinvip]

To use glibc to hack the guard jmpbuf from michaeltalyansky, please define the macro USE_LIBC_SETJMP, or make linux-debug EXTRA_CFLAGS="-DUSE_LIBC_SETJMP"

To use asm setjmp/longjmp from xzh3836598, please define the macro MD_USE_BUILTIN_SETJMP, or make linux-debug EXTRA_CFLAGS="-DMD_USE_BUILTIN_SETJMP"(default this solution).

For SRS3，you can pass the macro by configure：./configure --extra-flags='-DUSE_LIBC_SETJMP'

For some server which may do not define the macro __arm__, you can use configure to define it: ./configure --extra-flags='-D__arm__'

[yjlsmx]

为什么不支持mips呢？

[winlinvip]

MIPS貌似是可以支持的，ST本身那个就没有问题。
我对于寄存器不了解，这些PATCH都是别的大神做的。

[yjlsmx]

谢谢你的回复，我在wrtnode（国内 openwrt+mt7620 开源硬件）尝试过， srs-csdn/trunk/src/core/srs_core.hpp 里有个： #error "only support i386/amd64/x86_64/arm cpu"，编译失败，提示并不支持mips，为什么会有这个编译错误提示呢？

[winlinvip]

不确定其他的是不是支持，就检查了。你可以自己去掉。

[winlinvip]

User can use SRS3, or patch ST of SRS1/2 by:

1. Please remove the objs/st-1.9 and use this repository to replace it.
2. Enter cd objs/st-1.9 and build ST: https://github.com/ossrs/state-threads/tree/srs#usage
3. Build SRS and launch it.

[winlinvip]

为什么不支持mips呢？

正在支持，哈哈哈，#21