From 0314ff8522a6c991db26d5fb935e270d260e6dc0 Mon Sep 17 00:00:00 2001
From: Stephen Chen <tracelog@fb.com>
Date: Mon, 7 Aug 2017 09:32:27 -0700
Subject: [PATCH] aarch64: Use PTRACE_GETREGSET if available

In remote ptrace mode, we currently use PTRACE_PEEKUSER to read the registers.

PTRACE_PEEKUSER only works on x86 or arm 32 bit compatibility mode on linux. On aarch64 system,
it always return -EIO. https://github.com/torvalds/linux/blob/master/kernel/ptrace.c#L885-L1102

PTRACE_GETREGSET is the newer and more supported way of reading registers. Use that if it's available.
---
 configure.ac                 |  2 +-
 src/ptrace/_UPT_access_reg.c | 45 +++++++++++++++++++++++++++++++++++-
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index e11ba8bf..d4007535 100644
--- a/configure.ac
+++ b/configure.ac
@@ -56,7 +56,7 @@ AC_CHECK_TYPES([struct elf_prstatus, struct prstatus], [], [],
 #endif
 ])
 
-AC_CHECK_DECLS([PTRACE_POKEUSER, PTRACE_POKEDATA,
+AC_CHECK_DECLS([PTRACE_POKEUSER, PTRACE_POKEDATA, PTRACE_SETREGSET,
 PTRACE_TRACEME, PTRACE_CONT, PTRACE_SINGLESTEP,
 PTRACE_SYSCALL, PT_IO, PT_GETREGS,
 PT_GETFPREGS, PT_CONTINUE, PT_TRACE_ME,
diff --git a/src/ptrace/_UPT_access_reg.c b/src/ptrace/_UPT_access_reg.c
index ae71608b..ce25c783 100644
--- a/src/ptrace/_UPT_access_reg.c
+++ b/src/ptrace/_UPT_access_reg.c
@@ -34,7 +34,50 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 # include "tdep-ia64/rse.h"
 #endif
 
-#if HAVE_DECL_PTRACE_POKEUSER || HAVE_TTRACE
+#if HAVE_DECL_PTRACE_SETREGSET
+#include <sys/uio.h>
+int
+_UPT_access_reg (unw_addr_space_t as, unw_regnum_t reg, unw_word_t *val,
+                 int write, void *arg)
+{
+  struct UPT_info *ui = arg;
+  pid_t pid = ui->pid;
+  gregset_t regs;
+  char *r;
+  struct iovec loc;
+
+#if UNW_DEBUG
+  Debug(16, "using getregset: reg: %s [%u], val: %lx, write: %u\n", 
+	unw_regname(reg), (unsigned) reg, (long) val, write);
+
+  if (write)
+    Debug (16, "%s [%u] <- %lx\n", unw_regname (reg), (unsigned) reg, (long) *val);
+#endif
+  if ((unsigned) reg >= ARRAY_SIZE (_UPT_reg_offset))
+    {
+      errno = EINVAL;
+      goto badreg;
+    }
+
+  loc.iov_base = &regs;
+  loc.iov_len = sizeof(regs);
+
+  r = (char *)&regs + _UPT_reg_offset[reg];
+  if (ptrace (PTRACE_GETREGSET, pid, NT_PRSTATUS, &loc) == -1)
+    goto badreg;
+  if (write) {
+    memcpy(r, val, sizeof(unw_word_t));
+    if (ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &loc) == -1)
+      goto badreg;
+  } else
+    memcpy(val, r, sizeof(unw_word_t));
+  return 0;
+
+badreg:
+  Debug (1, "bad register %s [%u] (error: %s)\n", unw_regname(reg), reg, strerror (errno));
+  return -UNW_EBADREG;
+}
+#elif HAVE_DECL_PTRACE_POKEUSER || HAVE_TTRACE
 int
 _UPT_access_reg (unw_addr_space_t as, unw_regnum_t reg, unw_word_t *val,
                  int write, void *arg)