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Support OSX, the ST thread and stack model #11

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winlinvip opened this issue Mar 28, 2020 · 5 comments
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Support OSX, the ST thread and stack model #11

winlinvip opened this issue Mar 28, 2020 · 5 comments

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winlinvip commented Mar 28, 2020 •
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Analysis ST thread model, for mac __amd64__ or __x86_64__.
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The asm code:

    __st_md_cxt_save:

        /* Save SP */
        leaq 8(%rsp), %rdx              /* Save *(int64_t*)(rsp+8) to rdx, https://my.oschina.net/guonaihong/blog/508907 */
        movq %rdx, (JB_RSP*8)(%rdi)     /* Save rdx(rsp) to env[6], *(int64_t*)(rdi+6)=rdx */

which save RSP, the stack address to rdx, then save rdx to jmpbuf[JB_RSP].

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winlinvip commented Mar 28, 2020 •
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The asm code:

    __st_md_cxt_save:
        /* Save PC we are returning to */
        movq (%rsp), %rax               /* Save PC(parent function address) %(rsp) to rax */
        movq %rax, (JB_PC*8)(%rdi)      /* Save rax(PC) to env[7], *(int64_t*)(rdi+7)=rax */

which save the content of RSP, that is the previous function address(PC), to rax, then save rax to jmpbuf[JB_PC].

winlinvip added a commit that referenced this issue Mar 28, 2020
@winlinvip
Fix #11, Support OSX for Apple Darwin, macOS
91d530e
winlinvip referenced this issue in winlinvip/srs Mar 28, 2020
@winlinvip
Fix ossrs#1250, Support macOS, OSX, MacbookPro, Apple Darwin. 3.0.138
3556da4
@winlinvip winlinvip changed the title ST thread and stack model Support OSX, the ST thread and stack model Jul 29, 2021
@winlinvip winlinvip mentioned this issue Jul 29, 2021
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winlinvip commented Jul 29, 2021 •
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寄存器布局，osx和linux是一样的，参考：https://en.wikipedia.org/wiki/X86_calling_conventions

image

  • 函数参数：RDI, RSI, RDX, RCX, R8, R9
  • 返回值：RAX

由于save和restore最多只有两个参数：

        extern int _st_md_cxt_save(jmp_buf env);
        extern void _st_md_cxt_restore(jmp_buf env, int val);

因此，我们可以将其他的参数寄存器当作临时变量用，比如存储RSP和PC的内容：

  • rdx，在save时保存RSP的值到jmpbuf。现在改成了寄存器r8。
  • rax，在save时保存PC的值到jmpbuf。虽然rax是返回值，但是临时用下也可以。现在改成了寄存器r9。
    __st_md_cxt_save:
        /* Save SP */
        leaq 8(%rsp), %r8              /* Save *(int64_t*)(rsp+8) to r8, https://github.com/ossrs/state-threads/issues/11#issuecomment-888709759 */
        movq %r8, (JB_RSP*8)(%rdi)     /* Save r8(rsp) to env[6], *(int64_t*)(rdi+6)=r8 */
        /* Save PC we are returning to */
        movq (%rsp), %r9               /* Save PC(parent function address) %(rsp) to r9 */
        movq %r9, (JB_PC*8)(%rdi)      /* Save r9(PC) to env[7], *(int64_t*)(rdi+7)=r9 */
  • rdx，在restore时从jmpbuf恢复PC寄存器。现在改成了寄存器r8。
    __st_md_cxt_restore:
        /* Restore PC and RSP */
        movq (JB_PC*8)(%rdi), %r8      /* Load r8(PC) from env[7] */
        movq (JB_RSP*8)(%rdi), %rsp     /* Load rsp from env[6] */
        /* Jump to saved PC */
        jmpq *%r8                      /* Jump to r8(PC) */

Note: PC寄存器就是函数执行的地址。RSP是堆栈地址。

winlinvip added a commit that referenced this issue Jul 29, 2021
@winlinvip
OSX: Refine asm, add comments. #11
9ac6a82
winlinvip referenced this issue in ossrs/srs Jul 29, 2021
@winlinvip
ST: Refine OSX asm.
6ddef89
@winlinvip winlinvip mentioned this issue Sep 30, 2021
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