From: Jinyang He <hejinyang@loongson.cn>
To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 3/5] MIPS: Jump to kernel linked address by PC relative way
Date: Mon, 12 Apr 2021 20:28:12 +0800 [thread overview]
Message-ID: <1618230494-6207-4-git-send-email-hejinyang@loongson.cn> (raw)
In-Reply-To: <1618230494-6207-1-git-send-email-hejinyang@loongson.cn>
Commit 15ad838d281b ("[MIPS] Always do the ARC64_TWIDDLE_PC thing.")
gives the kernel a chance to jump to the address the kernel is linked to.
It can be seen from the old records that this situation is usually a jump
from XPHYS to KSEG0. For example, kdump operation, kexec_start_address is
usually in XPHYS on Loongson64 platform. Jumping from XPHYS to KSEG0 is a
big jump. With the relocation, there may be small jumps. As follows,
+-----------+
| |
|___________|
| |
| _kernel |
| |
|_\0: |
| jr t0 |---+
| la t0, \0 | |
|___________| |
| | |
| | |
|___________| |
| | |
| kernel | |
| | |
|\0: |<--+
| jr t0 |
| la t0, \0 |
| |
|___________|
| |
+-----------+
_kernel is same as kernel, only the loaded address is different. They are
all in KSEG0. For kernel, `jr t0` is right operation and PC will jump to
\0. For _kernel, `jr t0` is dangerous operation and PC will not jump to
_\0 because `la t0, \0` target address is not PC relative.
This patch get the PC address by fixed `1:` (t0) and dynamic ra at
`1:` (t1). t0 determines the PC Region of the address where the kernel is
linked to. t1 determines the offset relative to the PC Region.
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
---
arch/mips/kernel/head.S | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/mips/kernel/head.S b/arch/mips/kernel/head.S
index a25af1d..0186285 100644
--- a/arch/mips/kernel/head.S
+++ b/arch/mips/kernel/head.S
@@ -79,6 +79,9 @@ FEXPORT(__kernel_entry)
j kernel_entry
#endif /* CONFIG_BOOT_RAW */
+#define PC_REGION_SHIFT 28
+#define PC_REGION_MASK (~(1 << PC_REGION_SHIFT - 1))
+
__REF
NESTED(kernel_entry, 16, sp) # kernel entry point
@@ -89,9 +92,17 @@ NESTED(kernel_entry, 16, sp) # kernel entry point
/* We might not get launched at the address the kernel is linked to,
so we jump there. */
- PTR_LA t0, 0f
- jr t0
-0:
+ PTR_LA t0, 1f
+ bal 1f
+1: move t1, ra
+ PTR_LI t2, PC_REGION_MASK
+ and t0, t2
+ PTR_LI t2, ~PC_REGION_MASK
+ and t1, t2
+ or t0, t1
+ PTR_ADDIU t0, 2f-1b
+ jr t0
+2:
PTR_LA t0, __bss_start # clear .bss
LONG_S zero, (t0)
--
2.1.0
next prev parent reply other threads:[~2021-04-12 12:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-12 12:28 [PATCH v2 0/5] MIPS: relocate: Add automatic relocation to CONFIG_RELOCATABLE Jinyang He
2021-04-12 12:28 ` [PATCH v2 1/5] MIPS: relocate: Only compile relocs when CONFIG_RELOCATABLE is enabled Jinyang He
2021-04-12 12:28 ` [PATCH v2 2/5] MIPS: relocate: Use CONFIG_RANDOMIZE_BASE to enable kaslr Jinyang He
2021-04-12 12:28 ` Jinyang He [this message]
2021-04-12 12:28 ` [PATCH v2 4/5] MIPS: cavium-octeon: Execute the smp handle after jumping to kernel linked address Jinyang He
2021-04-12 12:28 ` [PATCH v2 5/5] MIPS: relocate: Add support to auto relocate kernel Jinyang He
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1618230494-6207-4-git-send-email-hejinyang@loongson.cn \
--to=hejinyang@loongson.cn \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=paulburton@kernel.org \
--cc=tsbogend@alpha.franken.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).