[hurd, commited] hurd: Add getcontext, makecontext, setcontext, swapcontext

[Samuel Thibault]

From: Thomas Schwinge <address@hidden>

Adapted from the Linux x86 functions.

Not thoroughly tested, but manual testing as well as glibc tests look fine, and
manual -lpthread testing also looks fine (within the given bounds for a new
stack to be used with makecontext).

This has also been in use in Debian since 2013.
---
 sysdeps/mach/hurd/i386/Makefile       |   4 +
 sysdeps/mach/hurd/i386/getcontext.S   |  74 +++++++++++++++
 sysdeps/mach/hurd/i386/makecontext.S  | 130 ++++++++++++++++++++++++++
 sysdeps/mach/hurd/i386/setcontext.S   |  93 ++++++++++++++++++
 sysdeps/mach/hurd/i386/swapcontext.S  | 110 ++++++++++++++++++++++
 sysdeps/mach/hurd/i386/ucontext_i.sym |  29 ++++++
 6 files changed, 440 insertions(+)
 create mode 100644 sysdeps/mach/hurd/i386/getcontext.S
 create mode 100644 sysdeps/mach/hurd/i386/makecontext.S
 create mode 100644 sysdeps/mach/hurd/i386/setcontext.S
 create mode 100644 sysdeps/mach/hurd/i386/swapcontext.S
 create mode 100644 sysdeps/mach/hurd/i386/ucontext_i.sym

diff --git a/sysdeps/mach/hurd/i386/Makefile b/sysdeps/mach/hurd/i386/Makefile
index 8404eb086c..2a7d138fff 100644
--- a/sysdeps/mach/hurd/i386/Makefile
+++ b/sysdeps/mach/hurd/i386/Makefile
@@ -106,3 +106,7 @@ ifeq ($(subdir),elf)
 # callbacks whose parameters don't permit to get the context parameters.
 check-execstack-xfail += ld.so libc.so libpthread.so
 endif
+
+ifeq ($(subdir),stdlib)
+gen-as-const-headers += ucontext_i.sym
+endif
diff --git a/sysdeps/mach/hurd/i386/getcontext.S 
b/sysdeps/mach/hurd/i386/getcontext.S
new file mode 100644
index 0000000000..cad6762db2
--- /dev/null
+++ b/sysdeps/mach/hurd/i386/getcontext.S
@@ -0,0 +1,74 @@
+/* Save current context.
+   Copyright (C) 2001-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <address@hidden>, 2001.
+
+   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)
+       /* Load address of the context data structure.  */
+       movl    4(%esp), %eax
+
+       /* Return value of getcontext.  EAX is the only register whose
+          value is not preserved.  */
+       movl    $0, oEAX(%eax)
+
+       /* Save the 32-bit register values and the return address.  */
+       movl    %ecx, oECX(%eax)
+       movl    %edx, oEDX(%eax)
+       movl    %edi, oEDI(%eax)
+       movl    %esi, oESI(%eax)
+       movl    %ebp, oEBP(%eax)
+       movl    (%esp), %ecx
+       movl    %ecx, oEIP(%eax)
+       leal    4(%esp), %ecx           /* Exclude the return address.  */
+       movl    %ecx, oESP(%eax)
+       movl    %ebx, oEBX(%eax)
+
+       /* Save the FS segment register.  We don't touch the GS register
+          since it is used for threads.  */
+       xorl    %edx, %edx
+       movw    %fs, %dx
+       movl    %edx, oFS(%eax)
+
+       leal    oFPREGS(%eax), %ecx
+       /* Save the floating-point context.  */
+       fnstenv (%ecx)
+       /* And load it right back since the processor changes the mask.
+          Intel thought this opcode to be used in interrupt handlers which
+          would block all exceptions.  */
+       fldenv  (%ecx)
+
+       /* Save the current signal mask.  */
+       subl    $12, %esp
+       cfi_adjust_cfa_offset (12)
+       leal    oSIGMASK(%eax), %eax
+       movl    %eax, 8(%esp)
+       movl    $0, 4(%esp)
+       movl    $SIG_BLOCK, (%esp)
+       call    HIDDEN_JUMPTARGET (__sigprocmask)
+       addl    $12, %esp
+       cfi_adjust_cfa_offset (-12)
+       /* Propagate %eax (and errno, in case).  */
+
+       ret
+PSEUDO_END(__getcontext)
+
+weak_alias (__getcontext, getcontext)
diff --git a/sysdeps/mach/hurd/i386/makecontext.S 
b/sysdeps/mach/hurd/i386/makecontext.S
new file mode 100644
index 0000000000..e2f8afc895
--- /dev/null
+++ b/sysdeps/mach/hurd/i386/makecontext.S
@@ -0,0 +1,130 @@
+/* Create new context.
+   Copyright (C) 2001-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <address@hidden>, 2001.
+
+   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(__makecontext)
+       movl    4(%esp), %eax
+
+       /* Load the address of the function we are supposed to run.  */
+       movl    8(%esp), %ecx
+
+       /* Compute the address of the stack.  The information comes from
+          to us_stack element.  */
+       movl    oSS_SP(%eax), %edx
+       movl    %ecx, oEIP(%eax)
+       addl    oSS_SIZE(%eax), %edx
+
+       /* Remember the number of parameters for the exit handler since
+          it has to remove them.  We store the number in the EBX register
+          which the function we will call must preserve.  */
+       movl    12(%esp), %ecx
+       movl    %ecx, oEBX(%eax)
+
+       /* Make room on the new stack for the parameters.
+          Room for the arguments, return address (== L(exitcode)) and
+          oLINK pointer is needed.  One of the pointer sizes is subtracted
+          after aligning the stack.  */
+       negl    %ecx
+       leal    -4(%edx,%ecx,4), %edx
+       negl    %ecx
+
+       /* Align the stack.  */
+       andl    $0xfffffff0, %edx
+       subl    $4, %edx
+
+       /* Store the future stack pointer.  */
+       movl    %edx, oESP(%eax)
+
+       /* Put the next context on the new stack (from the uc_link
+          element).  */
+       movl    oLINK(%eax), %eax
+       movl    %eax, 4(%edx,%ecx,4)
+
+       /* Copy all the parameters.  */
+       jecxz   2f
+1:     movl    12(%esp,%ecx,4), %eax
+       movl    %eax, (%edx,%ecx,4)
+       decl    %ecx
+       jnz     1b
+2:
+
+       /* If the function we call returns we must continue with the
+          context which is given in the uc_link element.  To do this
+          set the return address for the function the user provides
+          to a little bit of helper code which does the magic (see
+          below).  */
+#ifdef PIC
+       call    1f
+       cfi_adjust_cfa_offset (4)
+1:     popl    %ecx
+       cfi_adjust_cfa_offset (-4)
+       addl    $L(exitcode)-1b, %ecx
+       movl    %ecx, (%edx)
+#else
+       movl    $L(exitcode), (%edx)
+#endif
+       /* We need to terminate the FDE here instead of after ret because
+          the unwinder looks at ra-1 for unwind information.  */
+       cfi_endproc
+
+       /* 'makecontext' returns no value.  */
+       ret
+
+       /* 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.  */
+L(exitcode):
+       /* This removes the parameters passed to the function given to
+          'makecontext' from the stack.  EBX contains the number of
+          parameters (see above).  */
+       leal    (%esp,%ebx,4), %esp
+
+       cmpl    $0, (%esp)              /* Check the next context.  */
+       je      2f                      /* If it is zero exit.  */
+
+       call    HIDDEN_JUMPTARGET(__setcontext)
+       /* If this returns (which can happen if the syscall fails) we'll
+          exit the program with the return error value (-1).  */
+       jmp L(call_exit)
+
+2:
+       /* Exit with status 0.  */
+       xorl    %eax, %eax
+
+L(call_exit):
+       /* Align the stack and pass the exit code (from %eax).  */
+       andl    $0xfffffff0, %esp
+       subl    $12, %esp
+       pushl   %eax
+
+       call    HIDDEN_JUMPTARGET(exit)
+       /* The 'exit' call should never return.  In case it does cause
+          the process to terminate.  */
+       hlt
+       cfi_startproc
+END(__makecontext)
+
+weak_alias (__makecontext, makecontext)
diff --git a/sysdeps/mach/hurd/i386/setcontext.S 
b/sysdeps/mach/hurd/i386/setcontext.S
new file mode 100644
index 0000000000..ce6da9c47d
--- /dev/null
+++ b/sysdeps/mach/hurd/i386/setcontext.S
@@ -0,0 +1,93 @@
+/* Install given context.
+   Copyright (C) 2001-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <address@hidden>, 2001.
+
+   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)
+       /* Load address of the context data structure.  */
+       movl    4(%esp), %eax
+
+       /* Get the current signal mask.  */
+       subl    $12, %esp
+       cfi_adjust_cfa_offset (12)
+       movl    $0, 8(%esp)
+       leal    oSIGMASK(%eax), %eax
+       movl    %eax, 4(%esp)
+       movl    $SIG_SETMASK, (%esp)
+       call    HIDDEN_JUMPTARGET (__sigprocmask)
+       addl    $12, %esp
+       cfi_adjust_cfa_offset (-12)
+       testl   %eax, %eax
+       jne     L(pseudo_end)
+
+       /* EAX was modified, reload it.  */
+       movl    4(%esp), %eax
+
+       /* Restore the floating-point context.  Not the registers, only the
+          rest.  */
+       leal    oFPREGS(%eax), %ecx
+       fldenv  (%ecx)
+
+       /* Restore the FS segment register.  We don't touch the GS register
+          since it is used for threads.  */
+       movl    oFS(%eax), %ecx
+       movw    %cx, %fs
+
+       /* Fetch the address to return to.  */
+       movl    oEIP(%eax), %ecx
+
+       /* Load the new stack pointer.  */
+       cfi_def_cfa (eax, 0)
+       cfi_offset (edi, oEDI)
+       cfi_offset (esi, oESI)
+       cfi_offset (ebp, oEBP)
+       cfi_offset (ebx, oEBX)
+       cfi_offset (edx, oEDX)
+       cfi_offset (ecx, oECX)
+       movl    oESP(%eax), %esp
+
+       /* Push the return address on the new stack so we can return there.  */
+       pushl   %ecx
+
+       /* Load the values of all the 32-bit registers (except ESP).
+          Since we are loading from EAX, it must be last.  */
+       movl    oEDI(%eax), %edi
+       movl    oESI(%eax), %esi
+       movl    oEBP(%eax), %ebp
+       movl    oEBX(%eax), %ebx
+       movl    oEDX(%eax), %edx
+       movl    oECX(%eax), %ecx
+       movl    oEAX(%eax), %eax
+
+       /* End FDE here, we fall into another context.  */
+       cfi_endproc
+       cfi_startproc
+
+       /* The following 'ret' will pop the address of the code and jump
+          to it.  */
+
+L(pseudo_end):
+       ret
+PSEUDO_END(__setcontext)
+libc_hidden_def (__setcontext)
+
+weak_alias (__setcontext, setcontext)
diff --git a/sysdeps/mach/hurd/i386/swapcontext.S 
b/sysdeps/mach/hurd/i386/swapcontext.S
new file mode 100644
index 0000000000..45d1e2cb2b
--- /dev/null
+++ b/sysdeps/mach/hurd/i386/swapcontext.S
@@ -0,0 +1,110 @@
+/* Save current context and install the given one.
+   Copyright (C) 2001-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <address@hidden>, 2001.
+
+   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(__swapcontext)
+       /* Load address of the context data structure we save in.  */
+       movl    4(%esp), %eax
+
+       /* Return value of swapcontext.  EAX is the only register whose
+          value is not preserved.  */
+       movl    $0, oEAX(%eax)
+
+       /* Save the 32-bit register values and the return address.  */
+       movl    %ecx, oECX(%eax)
+       movl    %edx, oEDX(%eax)
+       movl    %edi, oEDI(%eax)
+       movl    %esi, oESI(%eax)
+       movl    %ebp, oEBP(%eax)
+       movl    (%esp), %ecx
+       movl    %ecx, oEIP(%eax)
+       leal    4(%esp), %ecx
+       movl    %ecx, oESP(%eax)
+       movl    %ebx, oEBX(%eax)
+
+       /* Save the FS segment register.  */
+       xorl    %edx, %edx
+       movw    %fs, %dx
+       movl    %edx, oFS(%eax)
+
+       leal    oFPREGS(%eax), %ecx
+       /* Save the floating-point context.  */
+       fnstenv (%ecx)
+
+       /* Load address of the context data structure we have to load.  */
+       movl    8(%esp), %ecx
+
+       /* Save the current signal mask and install the new one.  */
+       subl    $12, %esp
+       cfi_adjust_cfa_offset (12)
+       leal    oSIGMASK(%eax), %eax
+       movl    %eax, 8(%esp)
+       leal    oSIGMASK(%ecx), %eax
+       movl    %eax, 4(%esp)
+       movl    $SIG_SETMASK, (%esp)
+       call    HIDDEN_JUMPTARGET (__sigprocmask)
+       addl    $12, %esp
+       cfi_adjust_cfa_offset (-12)
+       testl   %eax, %eax
+       jne     L(pseudo_end)
+
+       /* EAX was modified, reload it.  */
+       movl    8(%esp), %eax
+
+       /* Restore the floating-point context.  Not the registers, only the
+          rest.  */
+       leal    oFPREGS(%eax), %ecx
+       fldenv  (%ecx)
+
+       /* Restore the FS segment register.  We don't touch the GS register
+          since it is used for threads.  */
+       movl    oFS(%eax), %edx
+       movw    %dx, %fs
+
+       /* Fetch the address to return to.  */
+       movl    oEIP(%eax), %ecx
+
+       /* Load the new stack pointer.  */
+       movl    oESP(%eax), %esp
+
+       /* Push the return address on the new stack so we can return there.  */
+       pushl   %ecx
+
+       /* Load the values of all the 32-bit registers (except ESP).
+          Since we are loading from EAX, it must be last.  */
+       movl    oEDI(%eax), %edi
+       movl    oESI(%eax), %esi
+       movl    oEBP(%eax), %ebp
+       movl    oEBX(%eax), %ebx
+       movl    oEDX(%eax), %edx
+       movl    oECX(%eax), %ecx
+       movl    oEAX(%eax), %eax
+
+       /* The following 'ret' will pop the address of the code and jump
+          to it.  */
+
+L(pseudo_end):
+       ret
+PSEUDO_END(__swapcontext)
+
+weak_alias (__swapcontext, swapcontext)
diff --git a/sysdeps/mach/hurd/i386/ucontext_i.sym 
b/sysdeps/mach/hurd/i386/ucontext_i.sym
new file mode 100644
index 0000000000..cc1cfd578d
--- /dev/null
+++ b/sysdeps/mach/hurd/i386/ucontext_i.sym
@@ -0,0 +1,29 @@
+#include <stddef.h>
+#include <signal.h>
+#include <sys/ucontext.h>
+
+--
+
+SIG_BLOCK
+SIG_SETMASK
+
+#define ucontext(member)       offsetof (ucontext_t, member)
+#define mcontext(member)       ucontext (uc_mcontext.member)
+#define mreg(reg)              mcontext (gregs[REG_##reg])
+
+oLINK          ucontext (uc_link)
+oSS_SP         ucontext (uc_stack.ss_sp)
+oSS_SIZE       ucontext (uc_stack.ss_size)
+oGS            mreg (GS)
+oFS            mreg (FS)
+oEDI           mreg (EDI)
+oESI           mreg (ESI)
+oEBP           mreg (EBP)
+oESP           mreg (ESP)
+oEBX           mreg (EBX)
+oEDX           mreg (EDX)
+oECX           mreg (ECX)
+oEAX           mreg (EAX)
+oEIP           mreg (EIP)
+oFPREGS                mcontext (fpregs)
+oSIGMASK       ucontext (uc_sigmask)
-- 
2.24.0