linux-kernel - [RFC PATCH V2 28/38] riscv: s64ilp32: Temporary workaround solution to gcc problem

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Date:   Sun, 12 Nov 2023 01:15:04 -0500
From:   guoren@...nel.org
To:     arnd@...db.de, guoren@...nel.org, palmer@...osinc.com,
        tglx@...utronix.de, conor.dooley@...rochip.com, heiko@...ech.de,
        apatel@...tanamicro.com, atishp@...shpatra.org, bjorn@...nel.org,
        paul.walmsley@...ive.com, anup@...infault.org, jiawei@...as.ac.cn,
        liweiwei@...as.ac.cn, wefu@...hat.com, U2FsdGVkX1@...il.com,
        wangjunqiang@...as.ac.cn, kito.cheng@...ive.com,
        andy.chiu@...ive.com, vincent.chen@...ive.com,
        greentime.hu@...ive.com, wuwei2016@...as.ac.cn, jrtc27@...c27.com,
        luto@...nel.org, fweimer@...hat.com, catalin.marinas@....com,
        hjl.tools@...il.com
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Guo Ren <guoren@...ux.alibaba.com>,
        LiaoShihua <shihua@...as.ac.cn>
Subject: [RFC PATCH V2 28/38] 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 e56ff39a79bc..1285736dadc4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -543,7 +543,7 @@ 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