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

[Flavio Cruz]

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