[PATCH] ARM / AArch64: Fix GetCmdLine semihosting directives

[Laurent Alfonsi <laurent dot alfonsi at st dot com>]

    All,

There's currently a problem in ARM & AArch64 crt0 on the GetCommandLine 
semihosting invocation.
I am proposing this patch to fix the issue.

Tested with versions : gcc 5.4, binutils 2.26, qemu-arm / qemu-aarch64 
2.5.0.

Would it be ok to commit ?

Regards,
Laurent Alfonsi


>From 12968a3744777fe4daac6a03cb76303e952664cc Mon Sep 17 00:00:00 2001
From: Laurent ALFONSI <laurent.alfonsi@st.com>
Date: Tue, 18 Apr 2017 17:50:16 +0200
Subject: [PATCH] ARM/AArch64: Fix GetCmdLine semihosting directives

When simulating arm code, the target program startup code (crt0) uses
semihosting invocations to get the command line from the simulator. The
simulator returns the command line and its size into the area passed in
parameter. (ARM 32-bit specifications :
http://infocenter.arm.com/help/topic/com.arm.doc.dui0058d/DUI0058.pdf
chapter "5.4.19 SYS_GET_CMDLINE").

The memory area pointed by the semihosting register argument is located
in .text section (usually not writtable (RX)).

If we run this code on a simulator that respects this rights properties
(qemu user-mode for instance), the command line will not be written to
the .text program memory, in particular the length of the string. The
program runs with an empty command line. This problem hasn't been seen
earlier probably because qemu user-mode is not so much used, but this can
happen with another simulator that refuse to write in a read-only segment.

With this modification, the command line can be correctly passed to the
target program.

Changes:
- libgloss/arm/crt0.S : Arguments passed to the AngelSWI_Reason_GetCmdLine
  semihosting invocation are placed into .data section instead of .text
- libgloss/aarch64/crt0.S : Idem for aarch64 AngelSVC_Reason_GetCmdLine
  semihosting.
---
 libgloss/aarch64/crt0.S | 11 +++++++----
 libgloss/arm/crt0.S     |  9 ++++++---
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/libgloss/aarch64/crt0.S b/libgloss/aarch64/crt0.S
index fdfc174..42673fb 100644
--- a/libgloss/aarch64/crt0.S
+++ b/libgloss/aarch64/crt0.S
@@ -166,11 +166,12 @@
 
 	/* Fetch and parse the command line.  */
 #ifdef ARM_RDI_MONITOR
-	adr	x1, .Lcmdline		/* Command line descriptor.  */
+	ldr	x1, .Lcmdline		/* Command line descriptor.  */
 	mov	w0, #AngelSVC_Reason_GetCmdLine
 	AngelSVCAsm AngelSVC
 #endif
 	ldr	x8, .Lcmdline
+	ldr	x8, [x8]
 
 	mov	x0, #0		/* argc */
 	mov	x1, sp		/* argv */
@@ -267,9 +268,8 @@ FUNCTION (_cpu_init_reset):
 .Lenvp:
 	GEN_DWORD env
 .Lcmdline:
-	GEN_DWORD CommandLine
-	.dword	511
-
+	GEN_DWORD AngelSVCArgs
+	
 /*  Workspace for Angel calls.  */
 	.data
 	.align 3
@@ -287,3 +287,6 @@ StackBase:	GEN_DWORD	__stack
 StackLimit:	.dword	0
 env:		.dword	0	/* Dummy environment array */
 CommandLine:	.space	512,0	/*  Maximum length of 511 chars handled.  */
+AngelSVCArgs:
+	GEN_DWORD CommandLine
+	.dword	511
diff --git a/libgloss/arm/crt0.S b/libgloss/arm/crt0.S
index 78bc467..709b71c 100644
--- a/libgloss/arm/crt0.S
+++ b/libgloss/arm/crt0.S
@@ -294,9 +294,10 @@ __change_mode:
 	movs	r1, r0
 #else
 	movs	r0, #AngelSWI_Reason_GetCmdLine
-	adr	r1, .LC30	/*  Space for command line */
+	ldr	r1, .LC30	/*  Space for command line */
 	AngelSWIAsm	AngelSWI
 	ldr	r1, .LC30
+	ldr	r1, [r1]
 #endif
 	/*  Parse string at r1 */
 	movs	r0, #0		/*  count of arguments so far */
@@ -503,8 +504,7 @@ change_back:
 #endif
 #ifdef ARM_RDI_MONITOR
 .LC30:
-	.word	CommandLine
-	.word	511
+	.word	AngelSWIArgs
 .LC31:
 	.word	__end__
 
@@ -517,6 +517,9 @@ HeapLimit:	.word	0
 __stack_base__:	.word	0
 StackLimit:	.word	0
 CommandLine:	.space	512,0	/*  Maximum length of 511 chars handled.  */
+AngelSWIArgs:
+	.word	CommandLine
+	.word	511
 #endif
 	
 #ifdef __pe__
-- 
1.9.1