Re: CVS commit: src/sys/arch/amd64

To: Masanobu SAITOH <msaitoh%execsw.org@localhost>
Subject: Re: CVS commit: src/sys/arch/amd64
From: Emmanuel Dreyfus <manu%netbsd.org@localhost>
Date: Thu, 26 Dec 2019 16:55:33 +0000

On Wed, Dec 25, 2019 at 05:05:11PM +0900, Masanobu SAITOH wrote:
> >> After this change, amd64 kernel does not boot on my HP Spectre x360
> >> 13-inch ae019TU laptop with pure UEFI boot mode.
>  I have a UEFI boot machine and it also doesn't boot well.

Please try the attached patch.

It adds the -n flag to ld, which disable auto-alignment of sections
in the file. I undestand alignement is highly desirable for userland
programs that may be mapped from file, but useless for the kernel,
which is just readen once by the bootloader.

Without auto-alignement, the .text segment starts right after the
ELF headers. This means the multiboot header can go in .text and
stay below 32k (as required by the multiboot specification). There
is no need for a multiboot section for that, and therefore no 
need to modify the linker script.

A side effect is that the kernel file shrinks of 2 MB, because there
is not an alignement hole between ELF headers and the .text section
anymore.

My patch also enable the MULTIBOOT option so that we can check
nothing gets broken with it. You can also try with the option
disabled, of course.

-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost

? sys/arch/amd64/compile/obj
? sys/arch/amd64/stand/prekern/obj
Index: sys/arch/amd64/amd64/locore.S
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/amd64/locore.S,v
retrieving revision 1.195
diff -U4 -r1.195 locore.S
--- sys/arch/amd64/amd64/locore.S	15 Dec 2019 02:58:21 -0000	1.195
+++ sys/arch/amd64/amd64/locore.S	26 Dec 2019 16:44:10 -0000
@@ -431,51 +431,8 @@
 	.size	tmpstk, tmpstk - .
 	.space	512
 tmpstk:
 
-.section multiboot,"a"
-#if defined(MULTIBOOT)
-	.align	8
-	.globl	Multiboot2_Header
-_C_LABEL(Multiboot2_Header):
-	.int	MULTIBOOT2_HEADER_MAGIC
-	.int	MULTIBOOT2_ARCHITECTURE_I386
-	.int	Multiboot2_Header_end - Multiboot2_Header
-	.int	-(MULTIBOOT2_HEADER_MAGIC + MULTIBOOT2_ARCHITECTURE_I386 \
-		+ (Multiboot2_Header_end - Multiboot2_Header))
-
-	.int	1	/* MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST */
-	.int	12	/* sizeof(multiboot_header_tag_information_request) */
-			/* + sizeof(uint32_t) * requests */
-	.int	4	/* MULTIBOOT_TAG_TYPE_BASIC_MEMINFO */
-	.align	8
-
-	.int	3	/* MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS */
-	.int	16	/* sizeof(struct multiboot_tag_efi64) */
-	.quad	(multiboot2_entry - KERNBASE)
-	.align	8
-
-	.int	9	/* MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI64 */
-	.int	16	/* sizeof(struct multiboot_tag_efi64) */
-	.quad	(multiboot2_entry - KERNBASE)
-	.align	8
-
-#if notyet
-	/*
-	 * Could be used to get an early console for debug,
-	 * but this is broken.
-	 */
-	.int	7	/* MULTIBOOT_HEADER_TAG_EFI_BS */
-	.int	8	/* sizeof(struct multiboot_tag) */
-	.align	8
-#endif
-
-	.int	0	/* MULTIBOOT_HEADER_TAG_END */
-	.int	8	/* sizeof(struct multiboot_tag) */
-	.align	8
-	.globl	Multiboot2_Header_end
-_C_LABEL(Multiboot2_Header_end):
-#endif	/* MULTIBOOT */
 
 /*
  * Some hackage to deal with 64bit symbols in 32 bit mode.
  * This may not be needed if things are cleaned up a little.
@@ -2179,8 +2136,50 @@
 SYSCALL_ENTRY	syscall,is_svs=0
 
 	TEXT_USER_BEGIN
 
+#if defined(MULTIBOOT)
+	.align	8
+	.globl	Multiboot2_Header
+_C_LABEL(Multiboot2_Header):
+	.int	MULTIBOOT2_HEADER_MAGIC
+	.int	MULTIBOOT2_ARCHITECTURE_I386
+	.int	Multiboot2_Header_end - Multiboot2_Header
+	.int	-(MULTIBOOT2_HEADER_MAGIC + MULTIBOOT2_ARCHITECTURE_I386 \
+		+ (Multiboot2_Header_end - Multiboot2_Header))
+
+	.int	1	/* MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST */
+	.int	12	/* sizeof(multiboot_header_tag_information_request) */
+			/* + sizeof(uint32_t) * requests */
+	.int	4	/* MULTIBOOT_TAG_TYPE_BASIC_MEMINFO */
+	.align	8
+
+	.int	3	/* MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS */
+	.int	16	/* sizeof(struct multiboot_tag_efi64) */
+	.quad	(multiboot2_entry - KERNBASE)
+	.align	8
+
+	.int	9	/* MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI64 */
+	.int	16	/* sizeof(struct multiboot_tag_efi64) */
+	.quad	(multiboot2_entry - KERNBASE)
+	.align	8
+
+#if notyet
+	/*
+	 * Could be used to get an early console for debug,
+	 * but this is broken.
+	 */
+	.int	7	/* MULTIBOOT_HEADER_TAG_EFI_BS */
+	.int	8	/* sizeof(struct multiboot_tag) */
+	.align	8
+#endif
+
+	.int	0	/* MULTIBOOT_HEADER_TAG_END */
+	.int	8	/* sizeof(struct multiboot_tag) */
+	.align	8
+	.globl	Multiboot2_Header_end
+_C_LABEL(Multiboot2_Header_end):
+#endif /* MULTIBOOT */
 #ifdef SVS
 SYSCALL_ENTRY	syscall_svs,is_svs=1
 #endif
 
Index: sys/arch/amd64/conf/GENERIC
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/conf/GENERIC,v
retrieving revision 1.551
diff -U4 -r1.551 GENERIC
--- sys/arch/amd64/conf/GENERIC	14 Dec 2019 07:45:20 -0000	1.551
+++ sys/arch/amd64/conf/GENERIC	26 Dec 2019 16:44:10 -0000
@@ -25,9 +25,9 @@
 #ident		"GENERIC-$Revision: 1.551 $"
 
 maxusers	64		# estimated number of users
 
-#options 	MULTIBOOT	# Multiboot support (see multiboot(8)) 
+options 	MULTIBOOT	# Multiboot support (see multiboot(8)) 
 
 # delay between "rebooting ..." message and hardware reset, in milliseconds
 #options 	CPURESET_DELAY=2000
 
Index: sys/arch/amd64/conf/Makefile.amd64
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/conf/Makefile.amd64,v
retrieving revision 1.80
diff -U4 -r1.80 Makefile.amd64
--- sys/arch/amd64/conf/Makefile.amd64	14 Nov 2019 16:23:52 -0000	1.80
+++ sys/arch/amd64/conf/Makefile.amd64	26 Dec 2019 16:44:10 -0000
@@ -90,12 +90,12 @@
 ## (5) link settings
 ##
 TEXTADDR?=	0xffffffff80200000
 .if defined(KASLR)
-EXTRA_LINKFLAGS=	--split-by-file=0x100000 -r -d
+EXTRA_LINKFLAGS=	--split-by-file=0x100000 -r -d -n
 KERNLDSCRIPT?= ${AMD64}/conf/kern.ldscript.kaslr
 .else
-EXTRA_LINKFLAGS=	-z max-page-size=0x200000
+EXTRA_LINKFLAGS=	-z max-page-size=0x200000 -n
 KERNLDSCRIPT?= ${AMD64}/conf/kern.ldscript
 .endif
 LINKFLAGS_NORMAL=	-X
 
Index: sys/arch/amd64/conf/kern.ldscript
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/conf/kern.ldscript,v
retrieving revision 1.30
diff -U4 -r1.30 kern.ldscript
--- sys/arch/amd64/conf/kern.ldscript	15 Dec 2019 02:56:40 -0000	1.30
+++ sys/arch/amd64/conf/kern.ldscript	26 Dec 2019 16:44:10 -0000
@@ -12,19 +12,9 @@
 
 ENTRY(_start)
 SECTIONS
 {
-	/*
-	 * multiboot (file_offset) : AT (load_address) 
-	 * file_offset must be below 32k for multiboot 2 specification
-	 * BIOS boot requires load_address above 0x200000
-	 */
-	multiboot 0x1000 : AT (0x200000)
-	{
-		. = ALIGN(8);
-		KEEP(*(multiboot));
-	}
-	.text : AT (0x200000 + SIZEOF(multiboot))
+	.text : AT (ADDR(.text) & 0x0fffffff)
 	{
 		. = ALIGN(__PAGE_SIZE);
 		__text_user_start = . ;
 		*(.text.user)

Follow-Ups:
- Re: CVS commit: src/sys/arch/amd64
  - From: Maxime Villard
- Re: CVS commit: src/sys/arch/amd64
  - From: Masanobu SAITOH

References:
- Re: CVS commit: src/sys/arch/amd64
  - From: Ryo ONODERA
- Re: CVS commit: src/sys/arch/amd64
  - From: Emmanuel Dreyfus
- Re: CVS commit: src/sys/arch/amd64
  - From: Masanobu SAITOH

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