[Libunwind-devel] [patch] [x86] Implement getcontext for x86

[Paul Pluzhnikov]

Greetings,

Attached patch implements getcontext for x86.

Motivation is the same as:
http://lists.nongnu.org/archive/html/libunwind-devel/2008-06/msg00009.html

This also fixes check-name-space on x86.

Tested on Linux/86 with no new failures.

Thanks,
--
Paul Pluzhnikov


diff --git a/include/libunwind-x86.h b/include/libunwind-x86.h
index 84da6e9..65d42ba 100644
--- a/include/libunwind-x86.h
+++ b/include/libunwind-x86.h
@@ -163,12 +163,6 @@ unw_tdep_save_loc_t;
 /* On x86, we can directly use ucontext_t as the unwind context.  */
 typedef ucontext_t unw_tdep_context_t;
 
-/* XXX this is not ideal: an application should not be prevented from
-   using the "getcontext" name just because it's using libunwind.  We
-   can't just use __getcontext() either, because that isn't exported
-   by glibc...  */
-#define unw_tdep_getcontext(uc)                (getcontext (uc), 0)
-
 #include "libunwind-dynamic.h"
 
 typedef struct
@@ -179,6 +173,9 @@ unw_tdep_proc_info_t;
 
 #include "libunwind-common.h"
 
+#define unw_tdep_getcontext            UNW_ARCH_OBJ(getcontext)
+extern int unw_tdep_getcontext (unw_tdep_context_t *);
+
 #define unw_tdep_is_fpreg              UNW_ARCH_OBJ(is_fpreg)
 extern int unw_tdep_is_fpreg (int);
 
diff --git a/src/Makefile.am b/src/Makefile.am
index e6e3b33..c110e76 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -227,7 +227,7 @@ libunwind_la_SOURCES_x86 = 
$(libunwind_la_SOURCES_x86_common)               \
        x86/Lcreate_addr_space.c x86/Lget_save_loc.c x86/Lglobal.c      \
        x86/Linit.c x86/Linit_local.c x86/Linit_remote.c                \
        x86/Lis_signal_frame.c x86/Lget_proc_info.c x86/Lregs.c         \
-       x86/Lresume.c x86/Lstep.c
+       x86/Lresume.c x86/Lstep.c x86/getcontext.S
 
 # The list of files that go into libunwind-x86:
 libunwind_x86_la_SOURCES_x86 = $(libunwind_la_SOURCES_x86_common)      \
diff --git a/src/x86/getcontext.S b/src/x86/getcontext.S
new file mode 100644
index 0000000..2f9b915
--- /dev/null
+++ b/src/x86/getcontext.S
@@ -0,0 +1,73 @@
+/* libunwind - a platform-independent unwind library
+   Copyright (C) 2009 Google, Inc
+       Contributed by Paul Pluzhnikov <address@hidden>
+
+This file is part of libunwind.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#include "offsets.h"
+
+/*  int _Ux86_getcontext (ucontext_t *ucp)
+
+  Saves the machine context in UCP necessary for libunwind.  
+  Unlike the libc implementation, we don't save the signal mask
+  and hence avoid the cost of a system call per unwind.
+  
+*/
+
+       .global _Ux86_getcontext
+       .type _Ux86_getcontext, @function
+_Ux86_getcontext:
+       mov     4(%esp),%eax  /* ucontext_t* */
+       
+       /* EAX is not preserved. */
+       movl    $0, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_EAX_OFF)(%eax)
+
+       movl    %ebx, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_EBX_OFF)(%eax)
+       movl    %ecx, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_ECX_OFF)(%eax)
+       movl    %edx, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_EDX_OFF)(%eax)
+       movl    %edi, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_EDI_OFF)(%eax)
+       movl    %esi, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_ESI_OFF)(%eax)
+       movl    %ebp, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_EBP_OFF)(%eax)
+
+       movl    (%esp), %ecx
+       movl    %ecx, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_EIP_OFF)(%eax)
+
+       leal    4(%esp), %ecx           /* Exclude the return address.  */
+       movl    %ecx, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_ESP_OFF)(%eax)
+
+       /* glibc getcontext saves GS, but not FS */
+       xorl    %ecx, %ecx
+       movw    %gs, %cx
+       movl    %ecx, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_FS_OFF)(%eax)
+
+       leal    LINUX_UC_FPREGS_MEM_OFF(%eax), %ecx
+       movl    %ecx, (LINUX_UC_MCONTEXT_OFF+LINUX_SC_FPSTATE_OFF)(%eax)
+       fnstenv (%ecx)
+       fldenv  (%ecx)
+
+       xor     %eax, %eax
+       ret
+
+#ifdef __linux__
+      /* We do not need executable stack.  */
+      .section        .note.GNU-stack,"",@progbits
+#endif
diff --git a/src/x86/offsets.h b/src/x86/offsets.h
index 96f06d1..94307c1 100644
--- a/src/x86/offsets.h
+++ b/src/x86/offsets.h
@@ -9,6 +9,7 @@
 #define LINUX_UC_STACK_OFF     0x08
 #define LINUX_UC_MCONTEXT_OFF  0x14
 #define LINUX_UC_SIGMASK_OFF   0x6c
+#define LINUX_UC_FPREGS_MEM_OFF        0xec
 
 /* The struct sigcontext is located at an offset of 4
    from the stack pointer in the signal frame.         */