[PATCH 02/12] gdbserver: Add optional runtime register set type.

["Schimpe, Christina" <christina.schimpe@intel.com>]

Some register sets can be activated and deactivated by the OS during the
runtime of a process.  One example register is the Intel CET shadow stack
pointer.  This adds a new type of register set to handle such cases.  We
shouldn't deactivate these regsets and should not show a warning if we
fail to read them.
---
 gdbserver/linux-low.cc | 40 ++++++++++++++++++++++++++++------------
 gdbserver/linux-low.h  |  7 ++++++-
 2 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index 50ce2b44927..355b28d9fe4 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -5007,23 +5007,31 @@ regsets_fetch_inferior_registers (struct regsets_info *regsets_info,
       if (res < 0)
 	{
 	  if (errno == EIO
-	      || (errno == EINVAL && regset->type == OPTIONAL_REGS))
+	      || (errno == EINVAL
+		  && (regset->type == OPTIONAL_REGS
+		      || regset->type == OPTIONAL_RUNTIME_REGS)))
 	    {
 	      /* If we get EIO on a regset, or an EINVAL and the regset is
-		 optional, do not try it again for this process mode.  */
+		 optional, do not try it again for this process mode.
+		 Even if the regset can be enabled at runtime it is safe
+		 to deactivate the regset in case of EINVAL, as we know
+		 the regset itself was the invalid argument of the ptrace
+		 call.  */
 	      disable_regset (regsets_info, regset);
 	    }
-	  else if (errno == ENODATA)
+	  else if (errno == ENODATA
+		   || (errno == ENODEV
+		       && regset->type == OPTIONAL_RUNTIME_REGS)
+		   || errno == ESRCH)
 	    {
-	      /* ENODATA may be returned if the regset is currently
-		 not "active".  This can happen in normal operation,
-		 so suppress the warning in this case.  */
-	    }
-	  else if (errno == ESRCH)
-	    {
-	      /* At this point, ESRCH should mean the process is
-		 already gone, in which case we simply ignore attempts
-		 to read its registers.  */
+	      /* ENODATA or ENODEV may be returned if the regset is
+		 currently not "active".  For ENODEV we additionally check
+		 if the register set is of type OPTIONAL_RUNTIME_REGS.
+		 This can happen in normal operation, so suppress the
+		 warning in this case.
+		 ESRCH should mean the process is already gone at this
+		 point, in which case we simply ignore attempts to read
+		 its registers.  */
 	    }
 	  else
 	    {
@@ -5111,6 +5119,14 @@ regsets_store_inferior_registers (struct regsets_info *regsets_info,
 		 optional, do not try it again for this process mode.  */
 	      disable_regset (regsets_info, regset);
 	    }
+	  else if (errno == ENODEV
+		   && regset->type == OPTIONAL_RUNTIME_REGS)
+	    {
+	      /* If we get ENODEV on a regset and the regset can be
+		 enabled at runtime try it again for this process mode.
+		 This can happen in normal operation, so suppress the
+		 warning in this case.  */
+	    }
 	  else if (errno == ESRCH)
 	    {
 	      /* At this point, ESRCH should mean the process is
diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
index 5be00b8c98c..da5aa26a993 100644
--- a/gdbserver/linux-low.h
+++ b/gdbserver/linux-low.h
@@ -42,7 +42,12 @@ enum regset_type {
   GENERAL_REGS,
   FP_REGS,
   EXTENDED_REGS,
-  OPTIONAL_REGS, /* Do not error if the regset cannot be accessed.  */
+  OPTIONAL_REGS, /* Do not error if the regset cannot be accessed.
+		    Disable the regset instead.  */
+  OPTIONAL_RUNTIME_REGS, /* Some optional regsets can only be accessed
+			    dependent on the execution flow.  For such
+			    access errors don't show a warning and don't
+			    disable the regset.  */
 };
 
 /* The arch's regsets array initializer must be terminated with a NULL
-- 
2.34.1

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