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Re: [Minios-devel] [UNIKRAFT PATCHv4 19/43] plat/kvm: Add link script for Arm64



Hi,

On 07/06/2018 10:03 AM, Wei Chen wrote:
This link script is based on x86 version, except following
differences:
1. Arm64 needs DTB to parse devices, and QEMU/KVM will revserve

s/revserve/reserved/

    the first 64KB of RAM as DTB area. In this case, we add a DTB
    section to this link script.

Do you mind giving a pointer to the QEMU/KVM layout? But then, do we really want to tie the linker script to QEMU layout?

2. We will use mmu to control each section's attribute, so the
    boundaries of sections with different memory attributes must
    be 4KiB alignment. For instance, the dtb section is readonly,
    but the text section  is readonly+exec. So the _text must start
    at a 4KiB alignment  address.

Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
---
  plat/kvm/arm/link64.ld | 111 +++++++++++++++++++++++++++++++++++++++++
  1 file changed, 111 insertions(+)
  create mode 100644 plat/kvm/arm/link64.ld

diff --git a/plat/kvm/arm/link64.ld b/plat/kvm/arm/link64.ld
new file mode 100644
index 0000000..8798a5b
--- /dev/null
+++ b/plat/kvm/arm/link64.ld
@@ -0,0 +1,111 @@
+/* SPDX-License-Identifier: ISC */

See previous e-mail on SPDX.

+/*
+ * Author(s): Dan Williams <djwillia@xxxxxxxxxx>
+ *            Martin Lucina <martin.lucina@xxxxxxxxxx>
+ *            Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
+ *            Wei Chen <wei.chen@xxxxxxx>
+ *
+ * Copyright (c) 2016, IBM
+ *           (c) 2016-2017 Docker, Inc.
+ *           (c) 2017, NEC Europe Ltd.
+ *           (c) 2018, Arm Ltd.
+ *
+ * Permission to use, copy, modify, and/or distribute this software
+ * for any purpose with or without fee is hereby granted, provided
+ * that the above copyright notice and this permission notice appear
+ * in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+ * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+ * AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+ * OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+ * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+OUTPUT_FORMAT("elf64-littleaarch64")
+OUTPUT_ARCH(aarch64)
+ENTRY(_libkvmplat_entry)
+
+/*
+ * We use mmu to control each section's attribute, so the boundaries
+ * of sections with different memory attributes must be 4KiB alignment.
+ * For instance, the dtb section is readonly, but the text section
+ * is readonly+exec. So the _text must start at a 4KiB alignment
+ * address.
+ */
+SECTIONS {
+       /* QEMU-AArch64 virt platform's ram base address */
+       . = 0x40000000;
+
+       /* Reserve first 64 KBytes for DTB */
+       _dtb = .;
+       . = . + 0x10000;

Please use a macro here to define 0x10000. This will be easier to see what is done.

+
+       /* Code */
+       _text = .;
+       .text :
+       {
+               *(.text)
+               *(.text.*)
+       }
+
+       . = ALIGN(0x1000);
+       _etext = .;
+
+       /* Read-only data */
+       _rodata = .;
+       .rodata :
+       {
+               *(.rodata)
+               *(.rodata.*)
+       }
+       .eh_frame :
+       {
+               *(.eh_frame)
+       }
+       _erodata = .;
+
+       /* Constructor tables (read-only) */
+       _ctors = .;
+       .preinit_array : {
+               . = ALIGN(0x8);
+               PROVIDE_HIDDEN (__preinit_array_start = .);
+               KEEP (*(.preinit_array))
+               PROVIDE_HIDDEN (__preinit_array_end = .);
+       }
+
+       .init_array : {
+               . = ALIGN(0x8);
+               PROVIDE_HIDDEN (__init_array_start = .);
+               KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) 
SORT_BY_INIT_PRIORITY(.ctors.*)))
+               KEEP (*(.init_array .ctors))
+               PROVIDE_HIDDEN (__init_array_end = .);
+       }
+       . = ALIGN(0x1000);

I guess, you want this to be page-aligned. If so, please use PAGE_SIZE.

+       _ectors = .;

I would move this before the . = ALIGN(...) to make clear the alignment is required for data.

+
+       /* Read-write data (initialized) */
+       _data = .;
+       .data :
+       {
+               *(.data)
+               *(.data.*)
+       }
+       _edata = .;
+
+       . = ALIGN(0x1000);

Same here.

+       __bss_start = .;
+       /* Read-write data (uninitialized) */

The word "uninitialized" is a bit misleading here. In C, this section should be Zeroed. So there are not really "unitialized".

This raise the question of who is going to initialize that region?

+       .bss :
+       {
+               *(.bss)
+               *(.bss.*)
+               *(COMMON)
+               . = ALIGN(0x1000);
+       }
+
+       _end = .;
+}


Cheers,

--
Julien Grall

--
Julien Grall

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