[PATCH 1/2] x86/boot: move early_serial_base to .data section

[PATCH 1/2] x86/boot: move early_serial_base to .data section

[Pingfan Liu]

arch/x86/boot/compressed/head_64.S clears BSS after relocated. If early
serial is set up before clearing BSS, the early_serial_base will be reset
to 0.

Initializing early_serial_base as -1 to push it to .data section.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jordan Borgner <mail@jordan-borgner.de>
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/boot/compressed/early_serial_console.c | 2 +-
 arch/x86/boot/early_serial_console.c            | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/early_serial_console.c b/arch/x86/boot/compressed/early_serial_console.c
index 261e81f..624e334 100644
--- a/arch/x86/boot/compressed/early_serial_console.c
+++ b/arch/x86/boot/compressed/early_serial_console.c
@@ -1,5 +1,5 @@
 #include "misc.h"
 
-int early_serial_base;
+int early_serial_base = -1;
 
 #include "../early_serial_console.c"
diff --git a/arch/x86/boot/early_serial_console.c b/arch/x86/boot/early_serial_console.c
index 023bf1c..d8de15a 100644
--- a/arch/x86/boot/early_serial_console.c
+++ b/arch/x86/boot/early_serial_console.c
@@ -149,6 +149,6 @@ void console_init(void)
 {
 	parse_earlyprintk();
 
-	if (!early_serial_base)
+	if (early_serial_base <= 0)
 		parse_console_uart8250();
 }
-- 
2.7.4

[PATCH 2/2] x86/boot: push console_init forward

[Pingfan Liu]

At the very early boot stage, early console is badly needed. Push its
initialization as early as possible, just after stack is ready.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jordan Borgner <mail@jordan-borgner.de>
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/boot/compressed/early_serial_console.c | 7 +++++++
 arch/x86/boot/compressed/head_64.S              | 4 ++++
 arch/x86/boot/compressed/misc.c                 | 1 -
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/early_serial_console.c b/arch/x86/boot/compressed/early_serial_console.c
index 624e334..223954a 100644
--- a/arch/x86/boot/compressed/early_serial_console.c
+++ b/arch/x86/boot/compressed/early_serial_console.c
@@ -3,3 +3,10 @@
 int early_serial_base = -1;
 
 #include "../early_serial_console.c"
+
+void early_console_init(void *rmode)
+{
+	boot_params = rmode;
+	console_init();
+	debug_putstr("early console is ready\n");
+}
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index fafb75c..e4a25f9 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -323,6 +323,10 @@ ENTRY(startup_64)
 	subq	$1b, %rdi
 
 	call	adjust_got
+	pushq	%rsi
+	movq	%rsi, %rdi
+	call	early_console_init
+	popq	%rsi
 
 	/*
 	 * At this point we are in long mode with 4-level paging enabled,
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index cafc6aa..475a3c6 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -368,7 +368,6 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 	lines = boot_params->screen_info.orig_video_lines;
 	cols = boot_params->screen_info.orig_video_cols;
 
-	console_init();
 	debug_putstr("early console in extract_kernel\n");
 
 	free_mem_ptr     = heap;	/* Heap */
-- 
2.7.4

Re: [PATCH 1/2] x86/boot: move early_serial_base to .data section

[Ingo Molnar]

* Pingfan Liu <kernelfans@gmail.com> wrote:

> arch/x86/boot/compressed/head_64.S clears BSS after relocated. If early
> serial is set up before clearing BSS, the early_serial_base will be reset
> to 0.
> 
> Initializing early_serial_base as -1 to push it to .data section.

I'm wondering whether it's wise to clear the BSS after relocation to 
begin with. It already gets cleared once, and an implicit zeroing of all 
fields on kernel relocation sounds dubious to me.

Is there a strong reason for that? I.e. is there some uninitialized or 
otherwise important-to-clear data there?

Thanks,

	Ingo

Re: [PATCH 1/2] x86/boot: move early_serial_base to .data section

[Pingfan Liu]

On Tue, May 7, 2019 at 4:28 PM Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Pingfan Liu <kernelfans@gmail.com> wrote:
>
> > arch/x86/boot/compressed/head_64.S clears BSS after relocated. If early
> > serial is set up before clearing BSS, the early_serial_base will be reset
> > to 0.
> >
> > Initializing early_serial_base as -1 to push it to .data section.
>
> I'm wondering whether it's wise to clear the BSS after relocation to
> begin with. It already gets cleared once, and an implicit zeroing of all
> fields on kernel relocation sounds dubious to me.
>
After reading the code more closely, I think that the BSS is not fully
initialized to 0, exception the stack and heap.

Furthermore the BSS is not copied to the target address. We just copy [0, _bss).
> Is there a strong reason for that? I.e. is there some uninitialized or
> otherwise important-to-clear data there?
>
I guess the reason may be stack or heap can contain some position
dependent data. (While in practice, there is no such kind of data in
the code now days)

Thanks,
Pingfan