[src/trunk]: src/lib/libc/arch/m68k Decorate the m68k signal trampoline with ...

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/a30897960e00
branches:  trunk
changeset: 1026396:a30897960e00
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Sun Nov 21 23:58:09 2021 +0000

description:
Decorate the m68k signal trampoline with the appropriate .cfi
directives to allow exception unwind / backtrace across a signal
handler.

diffstat:

 lib/libc/arch/m68k/genassym.cf       |  23 ++++++++++++++-
 lib/libc/arch/m68k/sys/__sigtramp2.S |  54 +++++++++++++++++++++++++++++++++++-
 2 files changed, 75 insertions(+), 2 deletions(-)

diffs (123 lines):

diff -r fb0f7deb9f83 -r a30897960e00 lib/libc/arch/m68k/genassym.cf
--- a/lib/libc/arch/m68k/genassym.cf    Sun Nov 21 23:34:44 2021 +0000
+++ b/lib/libc/arch/m68k/genassym.cf    Sun Nov 21 23:58:09 2021 +0000
@@ -1,4 +1,4 @@
-#      $NetBSD: genassym.cf,v 1.1 2013/07/17 01:41:17 matt Exp $
+#      $NetBSD: genassym.cf,v 1.2 2021/11/21 23:58:09 thorpej Exp $
 
 #
 # Copyright (c) 2013 The NetBSD Foundation, Inc.
@@ -36,11 +36,32 @@
 
 define UC_LINK         offsetof(ucontext_t, uc_link)
 define UC_SIGMASK      offsetof(ucontext_t, uc_sigmask)
+define UC_GREGS        offsetof(ucontext_t, uc_mcontext.__gregs[0])
 define UC_MCONTEXT_D0  offsetof(ucontext_t, uc_mcontext.__gregs[_REG_D0])
 define UC_MCONTEXT_SP  offsetof(ucontext_t, uc_mcontext.__gregs[_REG_A7])
 define UC_MCONTEXT_PC  offsetof(ucontext_t, uc_mcontext.__gregs[_REG_PC])
 define UC_SIZE         sizeof(ucontext_t)
 
+define _REG_D0         _REG_D0
+define _REG_D1         _REG_D1
+define _REG_D2         _REG_D2
+define _REG_D3         _REG_D3
+define _REG_D4         _REG_D4
+define _REG_D5         _REG_D5
+define _REG_D6         _REG_D6
+define _REG_D7         _REG_D7
+define _REG_A0         _REG_A0
+define _REG_A1         _REG_A1
+define _REG_A2         _REG_A2
+define _REG_A3         _REG_A3
+define _REG_A4         _REG_A4
+define _REG_A5         _REG_A5
+define _REG_A6         _REG_A6
+define _REG_A7         _REG_A7
+define _REG_PC         _REG_PC
+
+define SIZEOF_SIGINFO  sizeof(siginfo_t)
+
 define SC_ONSTACK      offsetof(struct sigcontext, sc_onstack)
 define SC___MASK13     offsetof(struct sigcontext, __sc_mask13)
 define SC_SP           offsetof(struct sigcontext, sc_sp)
diff -r fb0f7deb9f83 -r a30897960e00 lib/libc/arch/m68k/sys/__sigtramp2.S
--- a/lib/libc/arch/m68k/sys/__sigtramp2.S      Sun Nov 21 23:34:44 2021 +0000
+++ b/lib/libc/arch/m68k/sys/__sigtramp2.S      Sun Nov 21 23:58:09 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: __sigtramp2.S,v 1.4 2013/07/16 22:19:16 matt Exp $ */
+/*     $NetBSD: __sigtramp2.S,v 1.5 2021/11/21 23:58:09 thorpej Exp $ */
 
 /*-
  * Copyright (c) 2003 The NetBSD Foundation, Inc.
@@ -27,6 +27,7 @@
  */
 
 #include "SYS.h"
+#include "assym.h"
 
 /*
  * The m68k signal trampoline is invoked only to return from
@@ -39,7 +40,57 @@
  *             pointer to ucontext structure           [8]
  *             pointer to siginfo structure            [4]
  *     sp->    signal number                           [0]
+ *
+ * The DWARF register numbers are 0-7 (dX), 8-15 (aX), 16-23 (fpX),
+ * which maps nicely to _REG_D[0-7] and _REG_A[0-7].  For m68k, there
+ * is a DWARF pseudo-register for the return address, and additionally
+ * another DWARF pseudo-register for signal handler return addresses.
+ * We will specify both return address pseudo-registers (without
+ * explicitly specifying .cfi_return_column) to keep the compiler
+ * run-time happy with whichever one it decides to use.
  */
+
+#define        DWARF_RETURN_REG                24
+#if defined(__LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__)
+#define        DWARF_SIGRETURN_REG             __LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__
+#else
+#define        DWARF_SIGRETURN_REG             25
+#endif
+
+#define        CFI_OFFSET_DWARF_REG(d, r)      .cfi_offset d, r * 4
+#define        CFI_OFFSET(r)                   CFI_OFFSET_DWARF_REG(r, r)
+
+       .text
+       .cfi_startproc simple
+       .cfi_signal_frame
+       .cfi_def_cfa _REG_A7, 12 + SIZEOF_SIGINFO + UC_GREGS
+       CFI_OFFSET(_REG_D0)
+       CFI_OFFSET(_REG_D1)
+       CFI_OFFSET(_REG_D2)
+       CFI_OFFSET(_REG_D3)
+       CFI_OFFSET(_REG_D4)
+       CFI_OFFSET(_REG_D5)
+       CFI_OFFSET(_REG_D6)
+       CFI_OFFSET(_REG_D7)
+       CFI_OFFSET(_REG_A0)
+       CFI_OFFSET(_REG_A1)
+       CFI_OFFSET(_REG_A2)
+       CFI_OFFSET(_REG_A3)
+       CFI_OFFSET(_REG_A4)
+       CFI_OFFSET(_REG_A5)
+       CFI_OFFSET(_REG_A6)
+       CFI_OFFSET(_REG_A7)
+       CFI_OFFSET_DWARF_REG(DWARF_RETURN_REG, _REG_PC)
+       CFI_OFFSET_DWARF_REG(DWARF_SIGRETURN_REG, _REG_PC)
+
+/*
+ * The unwind entry includes one instruction slot prior to the trampoline
+ * because the unwinder will look up to (return PC - 1 insn) while unwinding.
+ * Normally this would be the jump / branch, but since there isn't one in
+ * this case, we place an explicit nop there instead.
+ */
+       nop
+
 ENTRY_NOPROFILE(__sigtramp_siginfo_2)
        movl    8(%sp),%a0      /* get pointer to ucontext */
        movl    %a0,4(%sp)      /* put it in the argument slot */
@@ -47,4 +98,5 @@
        SYSTRAP(setcontext)
        movl    %d0,4(%sp)      /* error code */
        SYSTRAP(exit)           /* exit */
+       .cfi_endproc
 END(__sigtramp_siginfo_2)