Re: [PATCH][Newlib][AArch32] Add support for HLT to Mixed Mode models

[Tamar Christina <Tamar dot Christina at arm dot com>]

Hi Corinna,

So sorry, I had been busy sending patches all day and forgot about the different
format for newlib.

I have updated my scripts to generate git format patches for newlib so it
shouldn't happen again!

Ok for master?

Thanks,
Tamar

The 02/07/2019 19:26, Corinna Vinschen wrote:
> On Feb  7 16:05, Tamar Christina wrote:
> > Hi All,
> > 
> > The Semihosting v2 protocol requires us to output the Armv8-a HLT instruction
> > when in mixed mode (SEMIHOST_V2_MIXED_MODE), however it also requires this to
> > be done for Armv7-a and earlier architectures.
> > 
> > The HLT instruction is defined in the undefined encoding space for older
> > architectures but simulators such as QEMU already trap on it [1] for all
> > architectures and is a requirement for semihosting v2 [2]
> > 
> > Unfortunately the GAS restricts the use of HLT to Armv8-a which requires us to
> > use the instruction encodings we want directly in crt0.
> > 
> > This patch does this, I have not updated newlib/libc/* as that is quite out of
> > date already.  A proper sync is needed in order to get things back in sync.
> > 
> > A different patch for this would be best.
> > 
> > [1] https://github.com/qemu/qemu/commit/19a6e31c9d2701ef648b70ddcfc3bf64cec8c37e
> > [2] https://developer.arm.com/docs/100863/latest/the-semihosting-interface
> > 
> > Regtested on arm-none-eabi and no issues.
> > 
> > Ok for trunk?
> 
> Sorry, no.
> 
> > Thanks,
> > Tamar
> > 
> > libgloss/ChangeLog:
> > 
> > 2019-02-07  Tamar Christina  <tamar.christina@arm.com>
> > 
> > 	PR libgloss/24070
> > 	* arm/crt0.S: Convert macros to function Macros.
> > 	* arm/swi.h (AngelSWI_ARM, AngelSWI): Use raw insn encoding for
> > 	SEMIHOST_V2_MIXED_MODE case.
> > 	(AngelSWIAsm): Make function.
> > 	(AngelSWIInsn, AngelSWIAsm): Use .inst directive as instruction.
> 
> Did you have a look into libgloss/ChangeLog lately?  We're using git for
> three years now.  Please provide patches in git format-patch format and
> provide a normal git log entry explaining what the patch does and why.
> We don't do CVS ChangeLogs anymore.
> 
> 
> Thanks,
> Corinna
> 
> -- 
> Corinna Vinschen
> Cygwin Maintainer
> Red Hat



-- 

From 2f69cf1de05cdd124195574df5b7bef4a43481e3 Mon Sep 17 00:00:00 2001
From: Tamar Christina <tamar.christina@arm.com>
Date: Wed, 6 Feb 2019 11:27:12 +0000
Subject: [PATCH] AArch32: Add support for HLT to Mixed Mode models

The Semihosting v2 protocol requires us to output the Armv8-a HLT instruction
when in mixed mode (SEMIHOST_V2_MIXED_MODE), however it also requires this to
be done for Armv7-a and earlier architectures.

The HLT instruction is defined in the undefined encoding space for older
architectures but simulators such as QEMU already trap on it [1] for all
architectures and is a requirement for semihosting v2 [2].

Unfortunately the GAS restricts the use of HLT to Armv8-a which requires us to
use the instruction encodings we want directly in crt0.

This patch does this, I have not updated newlib/libc/* as that is quite out of
date already.  A proper sync is needed in order to get things back in sync.

A different patch for this would be best.

[1] https://github.com/qemu/qemu/commit/19a6e31c9d2701ef648b70ddcfc3bf64cec8c37e
[2] https://developer.arm.com/docs/100863/latest/the-semihosting-interface
---
 libgloss/arm/crt0.S |  6 +++---
 libgloss/arm/swi.h  | 14 ++++++++++----
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/libgloss/arm/crt0.S b/libgloss/arm/crt0.S
index 48f3d6b1db..c708f63d83 100644
--- a/libgloss/arm/crt0.S
+++ b/libgloss/arm/crt0.S
@@ -116,10 +116,10 @@
 	bkpt	AngelSWI
 #elif defined(__thumb2__)
 	/*  We are in thumb mode for startup on armv7 architectures. */
-	AngelSWIAsm	AngelSWI
+	AngelSWIAsm (AngelSWI)
 #else
 	/*  We are always in ARM mode for startup on pre armv7 archs. */
-	AngelSWIAsm	AngelSWI_ARM
+	AngelSWIAsm (AngelSWI_ARM)
 #endif
 	ldr	r0, .LC0	/*  point at values read */
 
@@ -297,7 +297,7 @@ __change_mode:
 #else
 	movs	r0, #AngelSWI_Reason_GetCmdLine
 	ldr	r1, .LC30	/*  Space for command line */
-	AngelSWIAsm	AngelSWI
+	AngelSWIAsm (AngelSWI)
 	ldr	r1, .LC30
 	ldr	r1, [r1]
 #endif
diff --git a/libgloss/arm/swi.h b/libgloss/arm/swi.h
index 67eb36b3fa..8f50ee7d9b 100644
--- a/libgloss/arm/swi.h
+++ b/libgloss/arm/swi.h
@@ -31,9 +31,9 @@
 
 /* Now the SWI numbers and reason codes for RDI (Angel) monitors.  */
 #if defined (SEMIHOST_V2) && defined (SEMIHOST_V2_MIXED_MODE)
-  #define AngelSWI_ARM			0xF000 /* HLT A32.  */
+  #define AngelSWI_ARM			0xE10F0070 /* HLT #0xF000 A32.  */
   #ifdef __thumb__
-    #define AngelSWI			0x3C /* HLT T32.  */
+    #define AngelSWI			0xBABC /* HLT #0x3c T32.  */
   #else /* __thumb__.  */
     #define AngelSWI			AngelSWI_ARM
   #endif /* __thumb__.  */
@@ -49,10 +49,16 @@
 /* For thumb only architectures use the BKPT instruction instead of SWI.  */
 #ifdef THUMB_VXM
   #define AngelSWIInsn			"bkpt"
-  #define AngelSWIAsm			bkpt
+  #define AngelSWIAsm(IMM)		bkpt IMM
+#elif defined (SEMIHOST_V2) && defined (SEMIHOST_V2_MIXED_MODE)
+  /* This is actually encoding the HLT instruction, however we don't have
+     support for this in older assemblers.  So we have to encode the
+     instruction manually.  */
+  #define AngelSWIInsn			".inst"
+  #define AngelSWIAsm(IMM)		.inst IMM
 #else
   #define AngelSWIInsn			"swi"
-  #define AngelSWIAsm			swi
+  #define AngelSWIAsm(IMM)		swi IMM
 #endif
 
 /* The reason codes:  */
-- 
2.20.1