linux-kernel - [RFC PATCH 22/22] riscv: s64ilp32: Temporary workaround solution to gcc problem

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Date:   Thu, 18 May 2023 09:10:13 -0400
From:   guoren@...nel.org
To:     arnd@...db.de, guoren@...nel.org, palmer@...osinc.com,
        tglx@...utronix.de, peterz@...radead.org, luto@...nel.org,
        conor.dooley@...rochip.com, heiko@...ech.de, jszhang@...nel.org,
        chenhuacai@...nel.org, apatel@...tanamicro.com,
        atishp@...shpatra.org, mark.rutland@....com, bjorn@...nel.org,
        paul.walmsley@...ive.com, catalin.marinas@....com, will@...nel.org,
        rppt@...nel.org, anup@...infault.org, shihua@...as.ac.cn,
        jiawei@...as.ac.cn, liweiwei@...as.ac.cn, luxufan@...as.ac.cn,
        chunyu@...as.ac.cn, tsu.yubo@...il.com, wefu@...hat.com,
        wangjunqiang@...as.ac.cn, kito.cheng@...ive.com,
        andy.chiu@...ive.com, vincent.chen@...ive.com,
        greentime.hu@...ive.com, corbet@....net, wuwei2016@...as.ac.cn,
        jrtc27@...c27.com
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: [RFC PATCH 22/22] riscv: s64ilp32: Temporary workaround solution to gcc problem

From: Guo Ren <guoren@...ux.alibaba.com>

There is an existing problem in 64ilp32 gcc that combines two pointers
in one register. Liao is solving that problem. Before he finishes the
job, we could prevent it with a simple noinline attribute, fortunately.

struct path {
	struct vfsmount *mnt;
	struct dentry *dentry;
} __randomize_layout;

struct nameidata {
        struct path     path;
        struct qstr     last;
        struct path     root;
...
} __randomize_layout;

	struct nameidata *nd
	...
	nd->path = nd->root;
6c88                	ld	a0,24(s1)
				^^ // Wrong arg of mntget
e088                	sd	a0,0(s1)
	// Need inserting "lw a0,0(s1)" here
	mntget(path->mnt);
2a6150ef          	jal	c01ce946 <mntget>

Any gcc helps are welcome :)

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
Cc: LiaoShihua <shihua@...as.ac.cn>
---
 fs/namei.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index edfedfbccaef..22a2ef77e074 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -541,7 +541,7 @@ EXPORT_SYMBOL(inode_permission);
  *
  * Given a path increment the reference count to the dentry and the vfsmount.
  */
-void path_get(const struct path *path)
+void noinline path_get(const struct path *path)
 {
 	mntget(path->mnt);
 	dget(path->dentry);
-- 
2.36.1