linux-kernel - [PATCH 4/7] openrisc: Add thread-local storage (TLS) support

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Message-Id: <1474036985-20981-5-git-send-email-shorne@gmail.com>
Date:   Fri, 16 Sep 2016 23:43:02 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Christian Svensson <blue@....nu>,
        Stafford Horne <shorne@...il.com>
Subject: [PATCH 4/7] openrisc: Add thread-local storage (TLS) support

From: Christian Svensson <blue@....nu>

Historically OpenRISC GCC has reserved r10 which we now use to hold
the thread pointer for thread-local storage (TLS).

Signed-off-by: Christian Svensson <blue@....nu>
Signed-off-by: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
Signed-off-by: Stafford Horne <shorne@...il.com>
---
 arch/openrisc/kernel/process.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/openrisc/kernel/process.c b/arch/openrisc/kernel/process.c
index 7095dfe..277123b 100644
--- a/arch/openrisc/kernel/process.c
+++ b/arch/openrisc/kernel/process.c
@@ -173,6 +173,19 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
 
 		if (usp)
 			userregs->sp = usp;
+
+		/*
+		 * For CLONE_SETTLS set "tp" (r10) to the TLS pointer passed to sys_clone.
+		 *
+		 * The kernel entry is:
+		 *	int clone (long flags, void *child_stack, int *parent_tid,
+		 *		int *child_tid, struct void *tls)
+		 *
+		 * This makes the source r7 in the kernel registers.
+		 */
+		if (clone_flags & CLONE_SETTLS)
+			userregs->gpr[10] = userregs->gpr[7];
+
 		userregs->gpr[11] = 0;	/* Result from fork() */
 
 		kregs->gpr[20] = 0;	/* Userspace thread */
-- 
2.7.4