diff mbox

Make muser-mode the default for LEON3

Message ID 1435068612-1477-1-git-send-email-cederman@gaisler.com
State New
Headers show

Commit Message

Daniel Cederman June 23, 2015, 2:10 p.m. UTC 
The muser-mode flag causes the CASA instruction for LEON3 to use the
user mode ASI. This is the correct behavior for almost all LEON3 targets.
For this reason it makes sense to make user mode the default.

gcc/ChangeLog:

2015-06-23  Daniel Cederman  <cederman@gaisler.com>

	* config/sparc/sparc.opt: Rename mask from USER_MODE to SV_MODE
	  and make it inverse to change default
	* config/sparc/sync.md: Only use supervisor ASI for CASA when in
	  supervisor mode
	* doc/invoke.texi: Document change of default
---
 gcc/config/sparc/sparc.opt | 4 ++--
 gcc/config/sparc/sync.md   | 6 +++---
 gcc/doc/invoke.texi        | 4 ++--
 3 files changed, 7 insertions(+), 7 deletions(-)

Comments

Eric Botcazou June 26, 2015, 7:58 a.m. UTC | #1 
> The muser-mode flag causes the CASA instruction for LEON3 to use the
> user mode ASI. This is the correct behavior for almost all LEON3 targets.

Do they lack the CASA instruction with supervisor-mode ASI?  What happens when 
the CASA instruction with user-mode ASI is executed in supervisor mode?
Daniel Cederman June 26, 2015, 12:06 p.m. UTC | #2 
>
> Do they lack the CASA instruction with supervisor-mode ASI?  What happens when
> the CASA instruction with user-mode ASI is executed in supervisor mode?
>

For all LEON3 (with CASA support) the CASA instruction works in 
supervisor-mode regardless of ASI used. In user-mode CASA only works 
with the user-mode ASI. So CASA with user-mode ASI works for both 
user-mode and supervisor-mode. By having user-mode ASI as default, one 
would not need to change flag when compiling user or kernel code.

On a few old LEON3 systems the CASA instruction only works in supervisor 
mode. Using the CASA instruction with the user-mode ASI on these systems 
is not legal and will cause a trap.
Eric Botcazou June 30, 2015, 9:36 a.m. UTC | #3 
> For all LEON3 (with CASA support) the CASA instruction works in
> supervisor-mode regardless of ASI used. In user-mode CASA only works
> with the user-mode ASI. So CASA with user-mode ASI works for both
> user-mode and supervisor-mode. By having user-mode ASI as default, one
> would not need to change flag when compiling user or kernel code.

Thanks, OK for mainline, 5 branch and 4.9 branch.
diff mbox

Patch

diff --git a/gcc/config/sparc/sparc.opt b/gcc/config/sparc/sparc.opt
index 93d24a6..85bf0bd 100644
--- a/gcc/config/sparc/sparc.opt
+++ b/gcc/config/sparc/sparc.opt
@@ -114,8 +114,8 @@  Target
 Optimize tail call instructions in assembler and linker
 
 muser-mode
-Target Report Mask(USER_MODE)
-Do not generate code that can only run in supervisor mode
+Target Report InverseMask(SV_MODE)
+Do not generate code that can only run in supervisor mode (default)
 
 mcpu=
 Target RejectNegative Joined Var(sparc_cpu_and_features) Enum(sparc_processor_type) Init(PROCESSOR_V7)
diff --git a/gcc/config/sparc/sync.md b/gcc/config/sparc/sync.md
index 7d00b10..2fabff5 100644
--- a/gcc/config/sparc/sync.md
+++ b/gcc/config/sparc/sync.md
@@ -222,10 +222,10 @@ 
 	  UNSPECV_CAS))]
   "TARGET_LEON3"
 {
-  if (TARGET_USER_MODE)
-    return "casa\t%1 0xa, %2, %0"; /* ASI for user data space.  */
-  else
+  if (TARGET_SV_MODE)
     return "casa\t%1 0xb, %2, %0"; /* ASI for supervisor data space.  */
+  else
+    return "casa\t%1 0xa, %2, %0"; /* ASI for user data space.  */
 }
   [(set_attr "type" "multi")])
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index b99ab1c..86b2a73 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -21305,8 +21305,8 @@  in a performance loss, especially for floating-point code.
 @opindex muser-mode
 @opindex mno-user-mode
 Do not generate code that can only run in supervisor mode.  This is relevant
-only for the @code{casa} instruction emitted for the LEON3 processor.  The
-default is @option{-mno-user-mode}.
+only for the @code{casa} instruction emitted for the LEON3 processor.  This
+is the default.
 
 @item -mno-faster-structs
 @itemx -mfaster-structs