Re: [PATCH glibc] Implement setcontext/getcontext/makecontext/swapcontext for Hurd x86_64

[Samuel Thibault]

Applied, thanks!!

Flavio Cruz, le sam. 17 févr. 2024 15:25:35 -0500, a ecrit:
> Tested with the tests provided by glibc plus some other toy examples.
> ---
>  sysdeps/mach/hurd/x86_64/Makefile          |   4 +
>  sysdeps/mach/hurd/x86_64/__start_context.S |  49 +++++++++
>  sysdeps/mach/hurd/x86_64/getcontext.S      |  68 ++++++++++++
>  sysdeps/mach/hurd/x86_64/makecontext.c     | 119 ++++++++++++++++++++
>  sysdeps/mach/hurd/x86_64/setcontext.S      |  96 +++++++++++++++++
>  sysdeps/mach/hurd/x86_64/swapcontext.S     | 120 +++++++++++++++++++++
>  6 files changed, 456 insertions(+)
>  create mode 100644 sysdeps/mach/hurd/x86_64/__start_context.S
>  create mode 100644 sysdeps/mach/hurd/x86_64/getcontext.S
>  create mode 100644 sysdeps/mach/hurd/x86_64/makecontext.c
>  create mode 100644 sysdeps/mach/hurd/x86_64/setcontext.S
>  create mode 100644 sysdeps/mach/hurd/x86_64/swapcontext.S
> 
> diff --git a/sysdeps/mach/hurd/x86_64/Makefile 
> b/sysdeps/mach/hurd/x86_64/Makefile
> index 80cf2eb6..2b43f5d6 100644
> --- a/sysdeps/mach/hurd/x86_64/Makefile
> +++ b/sysdeps/mach/hurd/x86_64/Makefile
> @@ -3,3 +3,7 @@ ifeq ($(subdir),conform)
>  # (missing SA_NOCLDWAIT)
>  conformtest-xfail-conds += x86_64-gnu
>  endif
> +
> +ifeq ($(subdir),stdlib)
> +sysdep_routines += __start_context
> +endif
> diff --git a/sysdeps/mach/hurd/x86_64/__start_context.S 
> b/sysdeps/mach/hurd/x86_64/__start_context.S
> new file mode 100644
> index 00000000..3cb4c6b5
> --- /dev/null
> +++ b/sysdeps/mach/hurd/x86_64/__start_context.S
> @@ -0,0 +1,49 @@
> +/* Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <sysdep.h>
> +
> +/* This is the helper code which gets called if a function which is
> +   registered with 'makecontext' returns.  In this case we have to
> +   install the context listed in the uc_link element of the context
> +   'makecontext' manipulated at the time of the 'makecontext' call.
> +   If the pointer is NULL the process must terminate.  */
> +
> +
> +ENTRY(__start_context)
> +     /* This removes the parameters passed to the function given to
> +        'makecontext' from the stack.  RBX contains the address
> +        on the stack pointer for the next context.  */
> +     movq    %rbx, %rsp
> +
> +     /* Don't use pop here so that stack is aligned to 16 bytes.  */
> +     movq    (%rsp), %rdi            /* This is the next context.  */
> +     testq   %rdi, %rdi
> +     je      2f                      /* If it is zero exit.  */
> +
> +     call    __setcontext
> +     /* If this returns (which can happen if __sigprocmask fails) we'll
> +        exit the program with the return error value (-1).  */
> +     movq    %rax,%rdi
> +
> +2:
> +     call    HIDDEN_JUMPTARGET(exit)
> +     /* The 'exit' call should never return.  In case it does cause
> +        the process to terminate.  */
> +L(hlt):
> +     hlt
> +END(__start_context)
> diff --git a/sysdeps/mach/hurd/x86_64/getcontext.S 
> b/sysdeps/mach/hurd/x86_64/getcontext.S
> new file mode 100644
> index 00000000..ef431be1
> --- /dev/null
> +++ b/sysdeps/mach/hurd/x86_64/getcontext.S
> @@ -0,0 +1,68 @@
> +/* Save current context.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <sysdep.h>
> +
> +#include "ucontext_i.h"
> +
> +
> +ENTRY(__getcontext)
> +     /* Save the preserved registers, the registers used for passing
> +        args, and the return address.  */
> +     movq    %rbx, oRBX(%rdi)
> +     movq    %rbp, oRBP(%rdi)
> +     movq    %r12, oR12(%rdi)
> +     movq    %r13, oR13(%rdi)
> +     movq    %r14, oR14(%rdi)
> +     movq    %r15, oR15(%rdi)
> +
> +     movq    %rdi, oRDI(%rdi)
> +     movq    %rsi, oRSI(%rdi)
> +     movq    %rdx, oRDX(%rdi)
> +     movq    %rcx, oRCX(%rdi)
> +     movq    %r8, oR8(%rdi)
> +     movq    %r9, oR9(%rdi)
> +
> +     movq    (%rsp), %rcx
> +     movq    %rcx, oRIP(%rdi)
> +     leaq    8(%rsp), %rcx           /* Exclude the return address.  */
> +     movq    %rcx, oRSP(%rdi)
> +
> +     /* We have separate floating-point register content memory on the
> +        stack.  We use the __fpregs_mem block in the context.  Set the
> +        links up correctly.  */
> +
> +     leaq    oFPREGSMEM(%rdi), %rcx
> +     movq    %rcx, oFPREGS(%rdi)
> +     /* Save the floating-point environment.  */
> +     fnstenv (%rcx)
> +     fldenv  (%rcx)
> +     stmxcsr oMXCSR(%rdi)
> +
> +     /* Save the current signal mask with
> +      * __sigprocmask(SIG_BLOCK, NULL, oSIGMASK(%rdi)); */
> +     leaq    oSIGMASK(%rdi), %rdx
> +     movq $0, %rsi
> +     movl $SIG_BLOCK, %edi
> +     call    HIDDEN_JUMPTARGET (__sigprocmask)
> +
> +     /* Propagate %rax (and errno, in case).  */
> +     ret
> +PSEUDO_END(__getcontext)
> +
> +weak_alias (__getcontext, getcontext)
> diff --git a/sysdeps/mach/hurd/x86_64/makecontext.c 
> b/sysdeps/mach/hurd/x86_64/makecontext.c
> new file mode 100644
> index 00000000..6990a777
> --- /dev/null
> +++ b/sysdeps/mach/hurd/x86_64/makecontext.c
> @@ -0,0 +1,119 @@
> +/* Create new context.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <sysdep.h>
> +#include <stdarg.h>
> +#include <stdint.h>
> +#include <ucontext.h>
> +
> +#include "ucontext_i.h"
> +
> +/* This implementation can handle any ARGC value but only
> +   normal integer parameters.
> +   makecontext sets up a stack and the registers for the
> +   user context. The stack looks like this:
> +               +-----------------------+
> +               | next context          |
> +               +-----------------------+
> +               | parameter 7-n         |
> +            +-----------------------+
> +            | trampoline address    |
> +    %rsp ->    +-----------------------+
> +
> +   The registers are set up like this:
> +     %rdi,%rsi,%rdx,%rcx,%r8,%r9: parameter 1 to 6
> +     %rbx   : address of next context
> +     %rsp   : stack pointer.
> +*/
> +
> +/* XXX: This implementation currently only handles integer arguments.
> +   To handle long int and pointer arguments the va_arg arguments needs
> +   to be changed to long and also the stdlib/tst-setcontext.c file needs
> +   to be changed to pass long arguments to makecontext.  */
> +
> +
> +void
> +__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
> +{
> +  extern void __start_context (void) attribute_hidden;
> +  greg_t *sp;
> +  unsigned int idx_uc_link;
> +  va_list ap;
> +  int i;
> +
> +  /* Generate room on stack for parameter if needed and uc_link.  */
> +  sp = (greg_t *) ((uintptr_t) ucp->uc_stack.ss_sp
> +                + ucp->uc_stack.ss_size);
> +  sp -= (argc > 6 ? argc - 6 : 0) + 1;
> +  /* Align stack and make space for trampoline address.  */
> +  sp = (greg_t *) ((((uintptr_t) sp) & -16L) - 8);
> +
> +  idx_uc_link = (argc > 6 ? argc - 6 : 0) + 1;
> +
> +  /* Setup context ucp.  */
> +  /* Address to jump to.  */
> +  ucp->uc_mcontext.gregs[REG_RIP] = (uintptr_t) func;
> +  /* Setup rbx.*/
> +  ucp->uc_mcontext.gregs[REG_RBX] = (uintptr_t) &sp[idx_uc_link];
> +  ucp->uc_mcontext.gregs[REG_RSP] = (uintptr_t) sp;
> +
> +  /* Setup stack.  */
> +  sp[0] = (uintptr_t) &__start_context;
> +  sp[idx_uc_link] = (uintptr_t) ucp->uc_link;
> +
> +  va_start (ap, argc);
> +  /* Handle arguments.
> +
> +     The standard says the parameters must all be int values.  This is
> +     an historic accident and would be done differently today.  For
> +     x86-64 all integer values are passed as 64-bit values and
> +     therefore extending the API to copy 64-bit values instead of
> +     32-bit ints makes sense.  It does not break existing
> +     functionality and it does not violate the standard which says
> +     that passing non-int values means undefined behavior.  */
> +  for (i = 0; i < argc; ++i)
> +    switch (i)
> +      {
> +      case 0:
> +     ucp->uc_mcontext.gregs[REG_RDI] = va_arg (ap, greg_t);
> +     break;
> +      case 1:
> +     ucp->uc_mcontext.gregs[REG_RSI] = va_arg (ap, greg_t);
> +     break;
> +      case 2:
> +     ucp->uc_mcontext.gregs[REG_RDX] = va_arg (ap, greg_t);
> +     break;
> +      case 3:
> +     ucp->uc_mcontext.gregs[REG_RCX] = va_arg (ap, greg_t);
> +     break;
> +      case 4:
> +     ucp->uc_mcontext.gregs[REG_R8] = va_arg (ap, greg_t);
> +     break;
> +      case 5:
> +     ucp->uc_mcontext.gregs[REG_R9] = va_arg (ap, greg_t);
> +     break;
> +      default:
> +     /* Put value on stack.  */
> +     sp[i - 5] = va_arg (ap, greg_t);
> +     break;
> +      }
> +  va_end (ap);
> +}
> +
> +
> +weak_alias (__makecontext, makecontext)
> diff --git a/sysdeps/mach/hurd/x86_64/setcontext.S 
> b/sysdeps/mach/hurd/x86_64/setcontext.S
> new file mode 100644
> index 00000000..99919ee2
> --- /dev/null
> +++ b/sysdeps/mach/hurd/x86_64/setcontext.S
> @@ -0,0 +1,96 @@
> +/* Install given context.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <sysdep.h>
> +
> +#include "ucontext_i.h"
> +
> +
> +ENTRY(__setcontext)
> +     /* Save argument since call will destroy it.  */
> +     pushq   %rdi
> +     cfi_adjust_cfa_offset(8)
> +
> +     /* Set the signal mask with
> +        __sigprocmask (SIG_SETMASK, mask, NULL).  */
> +     xorl    %edx, %edx
> +     leaq    oSIGMASK(%rdi), %rsi
> +     movl    $SIG_SETMASK, %edi
> +     call    HIDDEN_JUMPTARGET (__sigprocmask)
> +     /* Pop the pointer into RDX. The choice is arbitrary, but
> +        leaving RDI and RSI available for use later can avoid
> +        shuffling values.  */
> +     popq    %rdx
> +
> +     test    %rax, %rax
> +     jne     L(pseudo_end)
> +
> +     /* Restore the floating-point context.  Not the registers, only the
> +        rest.  */
> +     movq    oFPREGS(%rdx), %rcx
> +     fldenv  (%rcx)
> +     ldmxcsr oMXCSR(%rdx)
> +
> +     /* Load the new stack pointer, the preserved registers and
> +        registers used for passing args.  */
> +     cfi_def_cfa(%rdx, 0)
> +     cfi_offset(%rbx,oRBX)
> +     cfi_offset(%rbp,oRBP)
> +     cfi_offset(%r12,oR12)
> +     cfi_offset(%r13,oR13)
> +     cfi_offset(%r14,oR14)
> +     cfi_offset(%r15,oR15)
> +     cfi_offset(%rsp,oRSP)
> +     cfi_offset(%rip,oRIP)
> +
> +     movq    oRSP(%rdx), %rsp
> +     movq    oRBX(%rdx), %rbx
> +     movq    oRBP(%rdx), %rbp
> +     movq    oR12(%rdx), %r12
> +     movq    oR13(%rdx), %r13
> +     movq    oR14(%rdx), %r14
> +     movq    oR15(%rdx), %r15
> +
> +     /* The following ret should return to the address set with
> +     getcontext.  Therefore push the address on the stack.  */
> +     movq    oRIP(%rdx), %rcx
> +     pushq   %rcx
> +
> +     movq    oRSI(%rdx), %rsi
> +     movq    oRDI(%rdx), %rdi
> +     movq    oRCX(%rdx), %rcx
> +     movq    oR8(%rdx), %r8
> +     movq    oR9(%rdx), %r9
> +
> +     /* Setup finally %rdx.  */
> +     movq    oRDX(%rdx), %rdx
> +
> +     /* End FDE here, we fall into another context.  */
> +     cfi_endproc
> +     cfi_startproc
> +
> +     /* Clear rax to indicate success.  */
> +     xorl    %eax, %eax
> +L(pseudo_end):
> +     /* The following 'ret' will pop the address of the code and jump
> +        to it.  */
> +     ret
> +PSEUDO_END(__setcontext)
> +libc_hidden_def (__setcontext)
> +
> +weak_alias (__setcontext, setcontext)
> diff --git a/sysdeps/mach/hurd/x86_64/swapcontext.S 
> b/sysdeps/mach/hurd/x86_64/swapcontext.S
> new file mode 100644
> index 00000000..79718a1f
> --- /dev/null
> +++ b/sysdeps/mach/hurd/x86_64/swapcontext.S
> @@ -0,0 +1,120 @@
> +/* Save current context and install the given one.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <sysdep.h>
> +
> +#include "ucontext_i.h"
> +
> +
> +/* int __swapcontext (ucontext_t *oucp, const ucontext_t *ucp);
> +
> +  Saves the machine context in oucp such that when it is activated,
> +  it appears as if __swapcontextt() returned again, restores the
> +  machine context in ucp and thereby resumes execution in that
> +  context.
> +
> +  This implementation is intended to be used for *synchronous* context
> +  switches only.  Therefore, it does not have to save anything
> +  other than the PRESERVED state.  */
> +
> +ENTRY(__swapcontext)
> +     /* Save the preserved registers, the registers used for passing args,
> +        and the return address.  */
> +     movq    %rbx, oRBX(%rdi)
> +     movq    %rbp, oRBP(%rdi)
> +     movq    %r12, oR12(%rdi)
> +     movq    %r13, oR13(%rdi)
> +     movq    %r14, oR14(%rdi)
> +     movq    %r15, oR15(%rdi)
> +
> +     movq    %rdi, oRDI(%rdi)
> +     movq    %rsi, oRSI(%rdi)
> +     movq    %rdx, oRDX(%rdi)
> +     movq    %rcx, oRCX(%rdi)
> +     movq    %r8, oR8(%rdi)
> +     movq    %r9, oR9(%rdi)
> +
> +     movq    (%rsp), %rcx
> +     movq    %rcx, oRIP(%rdi)
> +     leaq    8(%rsp), %rcx           /* Exclude the return address.  */
> +     movq    %rcx, oRSP(%rdi)
> +
> +     /* We have separate floating-point register content memory on the
> +        stack.  We use the __fpregs_mem block in the context.  Set the
> +        links up correctly.  */
> +     leaq    oFPREGSMEM(%rdi), %rcx
> +     movq    %rcx, oFPREGS(%rdi)
> +     /* Save the floating-point environment.  */
> +     fnstenv (%rcx)
> +     stmxcsr oMXCSR(%rdi)
> +
> +
> +     /* The function call destroys some registers, save ucp.  */
> +     movq    %rsi, %r12
> +
> +     /* Save the current signal mask and install the new one with
> +        __sigprocmask (SIG_BLOCK, newset, oldset).  */
> +     leaq    oSIGMASK(%rdi), %rdx
> +     leaq    oSIGMASK(%rsi), %rsi
> +     movl    $SIG_SETMASK, %edi
> +     call    HIDDEN_JUMPTARGET (__sigprocmask)
> +     test    %rax, %rax
> +     jne     L(pseudo_end)
> +
> +     /* Restore destroyed register into RDX. The choice is arbitrary,
> +        but leaving RDI and RSI available for use later can avoid
> +        shuffling values.  */
> +     movq    %r12, %rdx
> +
> +     /* Restore the floating-point context.  Not the registers, only the
> +        rest.  */
> +     movq    oFPREGS(%rdx), %rcx
> +     fldenv  (%rcx)
> +     ldmxcsr oMXCSR(%rdx)
> +
> +     /* Load the new stack pointer and the preserved registers.  */
> +     movq    oRSP(%rdx), %rsp
> +     movq    oRBX(%rdx), %rbx
> +     movq    oRBP(%rdx), %rbp
> +     movq    oR12(%rdx), %r12
> +     movq    oR13(%rdx), %r13
> +     movq    oR14(%rdx), %r14
> +     movq    oR15(%rdx), %r15
> +
> +     /* The following ret should return to the address set with
> +     getcontext.  Therefore push the address on the stack.  */
> +     movq    oRIP(%rdx), %rcx
> +     pushq   %rcx
> +
> +     /* Setup registers used for passing args.  */
> +     movq    oRDI(%rdx), %rdi
> +     movq    oRSI(%rdx), %rsi
> +     movq    oRCX(%rdx), %rcx
> +     movq    oR8(%rdx), %r8
> +     movq    oR9(%rdx), %r9
> +
> +     /* Setup finally %rdx.  */
> +     movq    oRDX(%rdx), %rdx
> +
> +     /* Clear rax to indicate success.  */
> +     xorl    %eax, %eax
> +L(pseudo_end):
> +     ret
> +PSEUDO_END(__swapcontext)
> +
> +weak_alias (__swapcontext, swapcontext)
> -- 
> 2.39.2
> 

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.