[PATCH gcc] Hurd x86_64: add unwind support for signal trampoline code

[Flavio Cruz]

Tested with some simple toy examples where an exception is thrown in the
signal handler.

libgcc/ChangeLog:
        * config/i386/gnu-unwind.h: Support unwinding x86_64 signal frames.

Signed-off-by: Flavio Cruz <flaviocruz@gmail.com>
---
 libgcc/config/i386/gnu-unwind.h | 97 ++++++++++++++++++++++++++++++++-
 1 file changed, 94 insertions(+), 3 deletions(-)

diff --git a/libgcc/config/i386/gnu-unwind.h b/libgcc/config/i386/gnu-unwind.h
index 0751b5593d4..02b060ab4a5 100644
--- a/libgcc/config/i386/gnu-unwind.h
+++ b/libgcc/config/i386/gnu-unwind.h
@@ -32,9 +32,100 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  
If not, see
 
 #ifdef __x86_64__
 
-/*
- * TODO: support for 64 bits needs to be implemented.
- */
+#define MD_FALLBACK_FRAME_STATE_FOR x86_gnu_fallback_frame_state
+
+static _Unwind_Reason_Code
+x86_gnu_fallback_frame_state
+(struct _Unwind_Context *context, _Unwind_FrameState *fs)
+{
+  static const unsigned char gnu_sigtramp_code[] =
+  {
+    /* rpc_wait_trampoline: */
+    0x48, 0xc7, 0xc0, 0xe7, 0xff, 0xff, 0xff,    /* mov    $-25,%rax */
+    0x0f, 0x05,                                  /* syscall */
+    0x49, 0x89, 0x04, 0x24,                      /* mov    %rax,(%r12) */
+    0x48, 0x89, 0xdc,                            /* mov    %rbx,%rsp */
+
+    /* trampoline: */
+    0x5f,                                        /* pop    %rdi */
+    0x5e,                                        /* pop    %rsi */
+    0x5a,                                        /* pop    %rdx */
+    0x48, 0x83, 0xc4, 0x08,                      /* add    $0x8,%rsp */
+    0x41, 0xff, 0xd5,                            /* call   *%r13 */
+
+    /* RA HERE */
+    0x48, 0x8b, 0x7c, 0x24, 0x10,                /* mov    0x10(%rsp),%rdi */
+    0xc3,                                        /* ret */
+
+    /* firewall: */
+    0xf4,                                        /* hlt */
+  };
+
+  const size_t gnu_sigtramp_len = sizeof gnu_sigtramp_code;
+  const size_t gnu_sigtramp_tail = 7; /* length of tail after RA */
+
+  struct stack_contents {
+    void *sigreturn_addr;
+    void *sigreturn_returns_here;
+    struct sigcontext *return_scp;
+  } *stack_contents;
+  struct sigcontext *scp;
+  unsigned long usp;
+
+  unsigned char *adjusted_pc = (unsigned char*)(context->ra) +
+    gnu_sigtramp_tail - gnu_sigtramp_len;
+  if (memcmp (adjusted_pc, gnu_sigtramp_code, gnu_sigtramp_len))
+    return _URC_END_OF_STACK;
+
+  stack_contents = context->cfa;
+
+  scp = stack_contents->return_scp;
+  usp = scp->sc_ursp;
+
+  fs->regs.reg[0].loc.offset = (unsigned long)&scp->sc_rax - usp;
+  fs->regs.reg[1].loc.offset = (unsigned long)&scp->sc_rdx - usp;
+  fs->regs.reg[2].loc.offset = (unsigned long)&scp->sc_rcx - usp;
+  fs->regs.reg[3].loc.offset = (unsigned long)&scp->sc_rbx - usp;
+  fs->regs.reg[4].loc.offset = (unsigned long)&scp->sc_rsi - usp;
+  fs->regs.reg[5].loc.offset = (unsigned long)&scp->sc_rdi - usp;
+  fs->regs.reg[6].loc.offset = (unsigned long)&scp->sc_rbp - usp;
+  fs->regs.reg[8].loc.offset = (unsigned long)&scp->sc_r8 - usp;
+  fs->regs.reg[9].loc.offset = (unsigned long)&scp->sc_r9 - usp;
+  fs->regs.reg[10].loc.offset = (unsigned long)&scp->sc_r10 - usp;
+  fs->regs.reg[11].loc.offset = (unsigned long)&scp->sc_r11 - usp;
+  fs->regs.reg[12].loc.offset = (unsigned long)&scp->sc_r12 - usp;
+  fs->regs.reg[13].loc.offset = (unsigned long)&scp->sc_r13 - usp;
+  fs->regs.reg[14].loc.offset = (unsigned long)&scp->sc_r14 - usp;
+  fs->regs.reg[15].loc.offset = (unsigned long)&scp->sc_r15 - usp;
+  fs->regs.reg[16].loc.offset = (unsigned long)&scp->sc_rip - usp;
+
+  /* Register 7 is rsp  */
+  fs->regs.cfa_how = CFA_REG_OFFSET;
+  fs->regs.cfa_reg = 7;
+  fs->regs.cfa_offset = usp - (unsigned long) context->cfa;
+
+  fs->regs.how[0] = REG_SAVED_OFFSET;
+  fs->regs.how[1] = REG_SAVED_OFFSET;
+  fs->regs.how[2] = REG_SAVED_OFFSET;
+  fs->regs.how[3] = REG_SAVED_OFFSET;
+  fs->regs.how[4] = REG_SAVED_OFFSET;
+  fs->regs.how[5] = REG_SAVED_OFFSET;
+  fs->regs.how[6] = REG_SAVED_OFFSET;
+  fs->regs.how[8] = REG_SAVED_OFFSET;
+  fs->regs.how[9] = REG_SAVED_OFFSET;
+  fs->regs.how[10] = REG_SAVED_OFFSET;
+  fs->regs.how[11] = REG_SAVED_OFFSET;
+  fs->regs.how[12] = REG_SAVED_OFFSET;
+  fs->regs.how[13] = REG_SAVED_OFFSET;
+  fs->regs.how[14] = REG_SAVED_OFFSET;
+  fs->regs.how[15] = REG_SAVED_OFFSET;
+  fs->regs.how[16] = REG_SAVED_OFFSET;
+
+  fs->retaddr_column = 16;
+  fs->signal_frame = 1;
+
+  return _URC_NO_REASON;
+}
 
 #else /* ifdef __x86_64__  */
 
-- 
2.43.0