Re: [AArch64] libgloss nosys.specs

[Yao Qi <qiyaoltc at gmail dot com>]

On 17-08-08 12:46:02, Alexander Fedotov wrote:
> Hello
> 
> Could anyone describe main idea how to use newlib for AArch64
> baremetal with nosys.specs ?

It doesn't work, unfortunately.  I had some local patches to get it
working.

> 
> I'm observing following problems:
> 1. crt0.s always build with ARM_RDI_MONITOR, while ARM port has
> different way with rdimon-crt0.s. ARM rdimon.specs utilize
> rdimon-crt0.s, while AArch64 is not.

Revert this commit cd26662dc590235e27e17eec773c5a308e6d863f

> 2. how to run it with disabled semihosting and nosys.specs ? Core just
> stuck on HLT instruction on third line of _start ( AngelSVCAsm
> AngelSVC) and that's all.

Wrap them with #ifdef ARM_RDI_MONITOR.  libgloss/aarch64/crt0.S still
pulls in semi-hosting stuff unconditionally,

 1. Get memory layout (stack, heap) via semi-hosting.  You can wrap it
 by ARM_RDI_MONITOR, but give the stack a fixed value, like this,

           exposed here in the HeapInfo Angel call.  */
        ldr     x0, .LC0                /* point at returned values */
        ldr     x1, [x0, #8]            /* get heap_limit */
+#else
+       /* Set up the stack pointer to a fixed value.  */
+       ldr     x1, .Lstack
+#endif

@@ -243,6 +249,10 @@ FUNCTION (_cpu_init_hook):
        GEN_DWORD __bss_start__
 .LC2:
        GEN_DWORD __bss_end__
+
+.Lstack:
+       GEN_DWORD 0x800000

 It is a hack, but good enough to get my work done.  You need to give
 a reasonable stack address for your configuration.

 2. Get command line options via semi-hosting.  You can wrap it by
 ARM_RDI_MONITOR, and set argc 0 and argv = NULL, like this,

@@ -219,6 +220,11 @@
        and     x4, x1, ~15
        mov     sp, x4
 
+#else
+       mov     x0, #0  /* argc = 0 */
+       mov     x1, #0  /* argv = NULL */
+#endif
+
        bl      FUNCTION (main)
 
        b       FUNCTION (exit)         /* Cannot return.  */

 this change above is reasonable, IMO, and I plan to upstream it.

With these stuff put together, I managed to get executable running
compiled with --spec=nosys.specs.  I am not sure your target env, device
or simulator etc.  With nosys.specs, in my side, there is no instruction
to initialize FPU, and _start in crt0.S calls memset.  The first
instruction in memset is a FPU instruction, which triggers exception
because FPU is not initialized.  I have to explicitly initialize FPU in
crt0.S.

Hope it helps, and good luck!

-- 
Yao (齐尧)