[PATCH] Semihosting fix for AArch64 when heapinfo is not provided by debugger

[Alexander Fedotov <alfedotov at gmail dot com>]

Use the same approach as in ARM port for case when Debugger not
providing necessary info for semihosting.

Alex

From 4f2ac350345f1126fa491dc0a335a9e1da92817e Mon Sep 17 00:00:00 2001
From: Alexander Fedotov <alfedotov@gmail.com>
Date: Wed, 11 Oct 2017 14:52:20 +0300
Subject: [PATCH] Fixed semihosting for AArch64 when heapinfo parameters are
 not provided by debugger

---
 libgloss/aarch64/crt0.S     | 78 ++++++++++++++++++++++++++++++---------------
 libgloss/aarch64/syscalls.c |  7 +++-
 2 files changed, 59 insertions(+), 26 deletions(-)

diff --git a/libgloss/aarch64/crt0.S b/libgloss/aarch64/crt0.S
index f670e03..f831be1 100644
--- a/libgloss/aarch64/crt0.S
+++ b/libgloss/aarch64/crt0.S
@@ -102,33 +102,44 @@
 	ldr	x0, .LC0		/* point at returned values */
 	ldr	x1, [x0, #8]		/* get heap_limit */
 
+	/* Set __heap_limit.  */
+#ifdef __ILP32__
+	/* Sanity check on the __heap_limit.  */
+	tst	x1, #0xffffffff00000000
+	bne	.Linsanepar
+#endif
+	cmp     x1, xzr
+	beq     .LC4
+	adrp	x2, __heap_limit
+	add	x2, x2, #:lo12:__heap_limit
+	str     x1, [x2]
+.LC4:
+
+	ldr	x1, [x0]		/* get heap_base */
 #ifdef __ILP32__
 	/* Sanity check on the heap base.  */
-	ldr	x0, [x0]		/* get heap_base */
-	tst	x0, #0xffffffff00000000
-	beq	1f
-	/* Exit with 1 if the heap base is not within the 32-bit address
-	   space.  */
-	mov	x0, ADP_Stopped_ApplicationExit & 0xff
-	movk	x0, ADP_Stopped_ApplicationExit >> 16, lsl #16
-	adrp	x1, HeapBase	/* Reuse to construct the parameter block.  */
-	add	x1, x1, #:lo12:HeapBase
-	str	x0, [x1]
-	mov	x0, 1
-	str	x0, [x1, #8]
-	mov	w0, #AngelSVC_Reason_ReportException
-	AngelSVCAsm AngelSVC
-1:
-	/* For the sake of safety, set the stack base to the top end of
-	   the 32-bit address space if the returned value from the
-	   Angel API call is larger than or equal to 4 GiB.  */
 	tst	x1, #0xffffffff00000000
-	csinv	w1, w1, wzr, eq
+	bne	.Linsanepar
 #endif
-#else
-	/* Set up the stack pointer to a fixed value.  */
-	ldr     x1, .Lstack
+	cmp     x1, xzr
+	bne     .LC5
+	/* If the heap base value [x0, #0] is 0 then the heap base is actually
+	   at the end of program data (i.e. __end__) */
+	ldr     x1, .LC3
+	str     x1, [x0, #0]
+.LC5:
+	ldr	x1, [x0, #16] /* get stack_base */
+
+#ifdef __ILP32__
+	/* Sanity check on the stack_base.  */
+	tst	x1, #0xffffffff00000000
+	bne	.Linsanepar
+#endif
+	cmp	x1, xzr
+	bne	.LC6
 #endif
+	ldr     x1, .Lstack /*  Set up the stack pointer to a fixed value */
+.LC6:
 
 	/* Ensure quad-word stack alignment.  */
 	and	x0, x1, #~15
@@ -234,6 +245,22 @@
 
 	b	FUNCTION (exit)		/* Cannot return.  */
 
+#if defined (ARM_RDI_MONITOR) && defined (__ILP32__)
+.Linsanepar:
+	/* Exit with 1 if the parameter is not within the 32-bit address
+	   space.  */
+	mov	x1, ADP_Stopped_ApplicationExit & 0xff
+	movk	x1, ADP_Stopped_ApplicationExit >> 16, lsl #16
+	adrp	x0, HeapBase	/* Reuse to construct the parameter block.  */
+	add	x0, x0, #:lo12:HeapBase
+	str	x1, [x0]
+	mov	x1, 1
+	str	x1, [x0, #8]
+	mov	w1, #AngelSVC_Reason_ReportException
+	AngelSVCAsm AngelSVC
+	b       .
+#endif
+
 /* Function initializing exception vector table, flatmap, etc.
    Declared as weak symbol so that user can override this definition
    by linking in their own version of the function.  */
@@ -245,12 +272,13 @@ FUNCTION (_cpu_init_hook):
 #ifdef ARM_RDI_MONITOR
 .LC0:
 	GEN_DWORD HeapBase
-#else
+.LC3:
+	GEN_DWORD __end__
+#endif
 .Lstack:
 	GEN_DWORD __stack
-
 	.weak __stack
-#endif
+
 .LC1:
 	GEN_DWORD __bss_start__
 .LC2:
diff --git a/libgloss/aarch64/syscalls.c b/libgloss/aarch64/syscalls.c
index af206a1..4de4e0d 100644
--- a/libgloss/aarch64/syscalls.c
+++ b/libgloss/aarch64/syscalls.c
@@ -625,6 +625,9 @@ _getpid (int n __attribute__ ((unused)))
   return 1;
 }
 
+/* Heap limit returned from SYS_HEAPINFO Angel semihost call.  */
+ulong __heap_limit __attribute__ ((aligned (8))) = 0xcafedead;
+
 caddr_t
 _sbrk (int incr)
 {
@@ -637,7 +640,9 @@ _sbrk (int incr)
 
   prev_heap_end = heap_end;
 
-  if (heap_end + incr > stack_ptr)
+  if ((heap_end + incr > stack_ptr)
+      /* Honour heap limit if it's valid.  */
+      || ((__heap_limit != 0xcafedead) && (heap_end + incr > __heap_limit)))
     {
       /* Some of the libstdc++-v3 tests rely upon detecting
          out of memory errors, so do not abort here.  */
-- 
2.7.4