arm64: Add VG (Vector Granule) pseudo register

This allows remote only unwinding though an SVE
function that pushes SVE registers onto the stack[1].

The remote unwinder is responsible for providing the
value of the VG register at the time the sample was
taken.

[1]: https://github.com/ARM-software/abi-aa/blob/main/aadwarf64/aadwarf64.rst

Signed-off-by: James Clark <james.clark@arm.com>
Change-Id: I8a203b73b17cd4a07afc1fdc55ad11765d73e173

5 files changed, 18 insertions, 3 deletions

diff --git a/include/libunwind-aarch64.h b/include/libunwind-aarch64.h
index f71835ad..63be0530 100644
--- a/include/libunwind-aarch64.h
+++ b/include/libunwind-aarch64.h
@@ -122,6 +122,9 @@ typedef enum
     /* Pseudo-register */
     UNW_AARCH64_RA_SIGN_STATE = 34,
 
+    /* SVE Vector Granule pseudo register */
+    UNW_AARCH64_VG = 46,
+
     /* 128-bit FP/Advanced SIMD registers.  */
     UNW_AARCH64_V0 = 64,
     UNW_AARCH64_V1,
diff --git a/src/aarch64/Ginit.c b/src/aarch64/Ginit.c
index 34e5c39a..57f48467 100644
--- a/src/aarch64/Ginit.c
+++ b/src/aarch64/Ginit.c
@@ -46,6 +46,15 @@ unw_addr_space_t unw_local_addr_space = &local_addr_space;
 static inline void *
 uc_addr (unw_tdep_context_t *uc, int reg)
 {
+  if (reg == UNW_AARCH64_VG)
+    {
+      /*
+       * Support for saving the vector length in the context needs to be
+       * added to get_context() for this path to work.
+       */
+      Debug(1, "Accessing VG register from context is not supported\n");
+      return NULL;
+    }
 #ifdef __FreeBSD__
   if (reg >= UNW_AARCH64_X0 && reg < UNW_AARCH64_X30)
     return &uc->uc_mcontext.mc_gpregs.gp_x[reg];
diff --git a/src/aarch64/Gregs.c b/src/aarch64/Gregs.c
index 5ae47254..e6328c0a 100644
--- a/src/aarch64/Gregs.c
+++ b/src/aarch64/Gregs.c
@@ -86,6 +86,7 @@ tdep_access_reg (struct cursor *c, unw_regnum_t reg, unw_word_t *valp,
     case UNW_AARCH64_X29:
     case UNW_AARCH64_PC:
     case UNW_AARCH64_PSTATE:
+    case UNW_AARCH64_VG:
       loc = c->dwarf.loc[reg];
       break;
     case UNW_AARCH64_RA_SIGN_STATE:
diff --git a/src/aarch64/Gstep.c b/src/aarch64/Gstep.c
index d682a53c..560430eb 100644
--- a/src/aarch64/Gstep.c
+++ b/src/aarch64/Gstep.c
@@ -122,6 +122,7 @@ aarch64_handle_signal_frame (unw_cursor_t *cursor)
   c->dwarf.loc[UNW_AARCH64_SP]  = DWARF_MEM_LOC (c->dwarf, sc_addr + LINUX_SC_SP_OFF);
   c->dwarf.loc[UNW_AARCH64_PC]  = DWARF_MEM_LOC (c->dwarf, sc_addr + LINUX_SC_PC_OFF);
   c->dwarf.loc[UNW_AARCH64_PSTATE]  = DWARF_MEM_LOC (c->dwarf, sc_addr + LINUX_SC_PSTATE_OFF);
+  c->dwarf.loc[UNW_AARCH64_VG]  = DWARF_NULL_LOC;
 
   /* Set SP/CFA and PC/IP.  */
   dwarf_get (&c->dwarf, c->dwarf.loc[UNW_AARCH64_SP], &c->dwarf.cfa);
diff --git a/src/aarch64/init.h b/src/aarch64/init.h
index 5dab60bb..e7613296 100644
--- a/src/aarch64/init.h
+++ b/src/aarch64/init.h
@@ -30,6 +30,9 @@ common_init (struct cursor *c, unsigned use_prev_instr)
 {
   int ret, i;
 
+  for (i = UNW_AARCH64_PSTATE + 1; i < UNW_AARCH64_V0; ++i)
+    c->dwarf.loc[i] = DWARF_NULL_LOC;
+
   c->dwarf.loc[UNW_AARCH64_X0]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_X0);
   c->dwarf.loc[UNW_AARCH64_X1]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_X1);
   c->dwarf.loc[UNW_AARCH64_X2]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_X2);
@@ -65,6 +68,7 @@ common_init (struct cursor *c, unsigned use_prev_instr)
   c->dwarf.loc[UNW_AARCH64_PC]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_PC);
   c->dwarf.loc[UNW_AARCH64_PSTATE] = DWARF_REG_LOC (&c->dwarf,
                                                     UNW_AARCH64_PSTATE);
+  c->dwarf.loc[UNW_AARCH64_VG]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_VG);
   c->dwarf.loc[UNW_AARCH64_V0]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_V0);
   c->dwarf.loc[UNW_AARCH64_V1]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_V1);
   c->dwarf.loc[UNW_AARCH64_V2]  = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_V2);
@@ -98,9 +102,6 @@ common_init (struct cursor *c, unsigned use_prev_instr)
   c->dwarf.loc[UNW_AARCH64_V30] = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_V30);
   c->dwarf.loc[UNW_AARCH64_V31] = DWARF_REG_LOC (&c->dwarf, UNW_AARCH64_V31);
 
-  for (i = UNW_AARCH64_PSTATE + 1; i < UNW_AARCH64_V0; ++i)
-    c->dwarf.loc[i] = DWARF_NULL_LOC;
-
   ret = dwarf_get (&c->dwarf, c->dwarf.loc[UNW_AARCH64_PC], &c->dwarf.ip);
   if (ret < 0)
     return ret;