Re: [PATCH] ARM / AArch64: Fix GetCmdLine semihosting directives

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

Hi Jeff,

I regenerated the patch on top of master branch.
I can now apply using git am. Sorry about that.

I re-validated again on newlib master + gcc 5.4, binutils 2.26, qemu-arm 
/ qemu-aarch64 2.5.0 / afm.

Regards,
Laurent

On 05/17/17 22:18, Jeff Johnston wrote:
> Hi Laurent,
>
> I have no issues.  I would have expected someone from the group of arm 
> maintainers here to
> have commented.  That said, I cannot apply the patch using git am nor 
> patch -u -p1.  Could you try recreating the patch?
> There is mention of trailing white-space in the errors in addition to 
> mentioning that the patch will not apply.
>
> Regards,
>
> -- Jeff J.
>
>
> On Tue, May 2, 2017 at 8:46 AM, Laurent Alfonsi 
> <laurent.alfonsi@st.com <mailto:laurent.alfonsi@st.com>> wrote:
>
>         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 4b06ee8a7d5b3e0b134dd7e5f5d11ead2f223b26 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 | 10 ++++++----
 libgloss/arm/crt0.S     |  9 ++++++---
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/libgloss/aarch64/crt0.S b/libgloss/aarch64/crt0.S
index ae6264d..ed4dafc 100644
--- a/libgloss/aarch64/crt0.S
+++ b/libgloss/aarch64/crt0.S
@@ -156,10 +156,11 @@
 	bl	FUNCTION (_init)
 
 	/* Fetch and parse the command line.  */
-	adr	x1, .Lcmdline		/* Command line descriptor.  */
+	ldr	x1, .Lcmdline		/* Command line descriptor.  */
 	mov	w0, #AngelSVC_Reason_GetCmdLine
 	AngelSVCAsm AngelSVC
 	ldr	x8, .Lcmdline
+	ldr	x8, [x8]
 
 	mov	x0, #0		/* argc */
 	mov	x1, sp		/* argv */
@@ -239,9 +240,7 @@ FUNCTION (_cpu_init_hook):
 .Lenvp:
 	GEN_DWORD env
 .Lcmdline:
-	GEN_DWORD CommandLine
-	.dword	255
-
+	GEN_DWORD AngelSVCArgs
 /*  Workspace for Angel calls.  */
 	.data
 	.align 3
@@ -258,3 +257,6 @@ StackBase:	.dword	0
 StackLimit:	.dword	0
 env:		.dword	0	/* Dummy environment array */
 CommandLine:	.space	256,0	/*  Maximum length of 255 chars handled.  */
+AngelSVCArgs:
+	GEN_DWORD CommandLine
+	.dword	255
diff --git a/libgloss/arm/crt0.S b/libgloss/arm/crt0.S
index 35c306b..48f3d6b 100644
--- a/libgloss/arm/crt0.S
+++ b/libgloss/arm/crt0.S
@@ -296,9 +296,10 @@ __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 */
@@ -505,8 +506,7 @@ change_back:
 #endif
 #ifdef ARM_RDI_MONITOR
 .LC30:
-	.word	CommandLine
-	.word	255
+	.word	AngelSWIArgs
 .LC31:
 	.word	__end__
 
@@ -519,6 +519,9 @@ HeapLimit:	.word	0
 __stack_base__:	.word	0
 StackLimit:	.word	0
 CommandLine:	.space	256,0	/*  Maximum length of 255 chars handled.  */
+AngelSWIArgs:
+	.word	CommandLine
+	.word	255
 #endif
 	
 #ifdef __pe__
-- 
1.9.1