Make libunwind pass C++ exceptions correctly

When libunwind is linked with a C++ program that throws exceptions,
the exception that's thrown is passed in %rax. However, libc's
setcontext clears %rax, causing problems.

This patch implements a setcontext that doesn't clobber rax.

TBD: Add dwarf CFI annotations

Signed-off-by: Arun Sharma <arun.sharma@google.com>

3 files changed, 151 insertions, 3 deletions

diff --git a/src/x86_64/Gresume.c b/src/x86_64/Gresume.c
index 2fc51aab..4edc4da6 100644
--- a/src/x86_64/Gresume.c
+++ b/src/x86_64/Gresume.c
@@ -71,7 +71,7 @@ x86_64_local_resume (unw_addr_space_t as, unw_cursor_t *cursor, void *arg)
     {
       Debug (8, "resuming at ip=%llx via setcontext()\n",
 	     (unsigned long long) c->dwarf.ip);
-      setcontext (uc);
+      _x86_64_setcontext (uc);
     }
 #else
 # warning Implement me!
diff --git a/src/x86_64/gen-offsets.c b/src/x86_64/gen-offsets.c
new file mode 100644
index 00000000..343716db
--- /dev/null
+++ b/src/x86_64/gen-offsets.c
@@ -0,0 +1,73 @@
+#include <ucontext.h>
+#include <stdio.h>
+#include <stddef.h>
+
+#define REG_OFFSET(reg) (offsetof(struct ucontext, uc_mcontext.gregs[REG_##reg]))
+
+# define REG_R8		0
+# define REG_R9		1
+# define REG_R10	2
+# define REG_R11	3
+# define REG_R12	4
+# define REG_R13	5
+# define REG_R14	6
+# define REG_R15	7
+# define REG_RDI	8
+# define REG_RSI	9
+# define REG_RBP	10
+# define REG_RBX	11
+# define REG_RDX	12
+# define REG_RAX	13
+# define REG_RCX	14
+# define REG_RSP	15
+# define REG_RIP	16
+
+char *regs[] = { "RAX",
+	"RBX",
+	"RCX",
+	"RDX",
+	"RDI",
+	"RSI",
+	"RSP",
+	"RBP",
+	"R8",
+	"R9",
+	"R10",
+	"R11",
+	"R12",
+	"R13",
+	"R14",
+	"R15",
+	"RIP",
+	};
+
+main()
+{
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[0], REG_OFFSET(RAX));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[1], REG_OFFSET(RBX));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[2], REG_OFFSET(RCX));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[3], REG_OFFSET(RDX));
+
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[4], REG_OFFSET(RDI));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[5], REG_OFFSET(RSI));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[6], REG_OFFSET(RSP));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[7], REG_OFFSET(RBP));
+
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[8], REG_OFFSET(R8));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[9], REG_OFFSET(R9));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[10], REG_OFFSET(R10));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[11], REG_OFFSET(R11));
+
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[12], REG_OFFSET(R12));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[13], REG_OFFSET(R13));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[14], REG_OFFSET(R14));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[15], REG_OFFSET(R15));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[15], REG_OFFSET(R15));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[15], REG_OFFSET(R15));
+	printf("#define REG_OFFSET_%s\t%d\n" , regs[16], REG_OFFSET(RIP));
+
+	printf("#define REG_OFFSET_FPREGS_PTR\t%d\n" , offsetof(struct ucontext, uc_mcontext.fpregs));
+	printf("#define FPREG_OFFSET_MXCR\t%d\n" , offsetof(struct _libc_fpstate, mxcsr));
+}
+
+
diff --git a/src/x86_64/setcontext.S b/src/x86_64/setcontext.S
index d164d8db..d1578e1d 100644
--- a/src/x86_64/setcontext.S
+++ b/src/x86_64/setcontext.S
@@ -1,4 +1,79 @@
-	.global _UI_setcontext
+/* libunwind - a platform-independent unwind library
+   Copyright (C) 2007 Google, Inc
+	Contributed by Arun Sharma <arun.sharma@google.com>
 
-_UI_setcontext:
+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.  */
+
+#define REG_OFFSET_RAX  144
+#define REG_OFFSET_RBX  128
+#define REG_OFFSET_RCX  152
+#define REG_OFFSET_RDX  136
+#define REG_OFFSET_RDI  104
+#define REG_OFFSET_RSI  112
+#define REG_OFFSET_RSP  160
+#define REG_OFFSET_RBP  120
+#define REG_OFFSET_R8   40
+#define REG_OFFSET_R9   48
+#define REG_OFFSET_R10  56
+#define REG_OFFSET_R11  64
+#define REG_OFFSET_R12  72
+#define REG_OFFSET_R13  80
+#define REG_OFFSET_R14  88
+#define REG_OFFSET_R15  96
+#define REG_OFFSET_R15  96
+#define REG_OFFSET_R15  96
+#define REG_OFFSET_RIP  168
+#define REG_OFFSET_FPREGS_PTR   224
+#define FPREG_OFFSET_MXCR       24
+
+	.global _x86_64_setcontext
+
+_x86_64_setcontext:
+
+        /* restore fp state */
+	mov    REG_OFFSET_FPREGS_PTR(%rdi),%r8
+	fldenv (%r8)
+	ldmxcsr FPREG_OFFSET_MXCR(%r8)
+
+	/* restore the rest of the state */
+	mov    REG_OFFSET_R8(%rdi),%r8
+	mov    REG_OFFSET_R9(%rdi),%r9
+	mov    REG_OFFSET_RBX(%rdi),%rbx
+	mov    REG_OFFSET_RBP(%rdi),%rbp
+	mov    REG_OFFSET_R12(%rdi),%r12
+	mov    REG_OFFSET_R13(%rdi),%r13
+	mov    REG_OFFSET_R14(%rdi),%r14
+	mov    REG_OFFSET_R15(%rdi),%r15
+	mov    REG_OFFSET_RSI(%rdi),%rsi
+	mov    REG_OFFSET_RDX(%rdi),%rdx
+	mov    REG_OFFSET_RAX(%rdi),%rax
+	mov    REG_OFFSET_RCX(%rdi),%rcx
+	mov    REG_OFFSET_RSP(%rdi),%rsp
+
+        /* push the return address on the stack */
+	mov    REG_OFFSET_RIP(%rdi),%rcx
+	push   %rcx
+
+	mov    REG_OFFSET_RCX(%rdi),%rcx
+	mov    REG_OFFSET_RDI(%rdi),%rdi
 	retq
+