linux-kernel - [PATCH v2 20/76] ARC: [Review] Preparing to fix incorrect syscall restarts due to signals

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Message-ID: <1358511930-7424-21-git-send-email-vgupta@synopsys.com>
Date:	Fri, 18 Jan 2013 17:54:34 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	<linux-arch@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:	<arnd@...db.de>, Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: [PATCH v2 20/76] ARC: [Review] Preparing to fix incorrect syscall restarts due to signals

To avoid multiple syscall restarts (multiple signals) or no restart at
all (sigreturn), we need just an extra bit of state "literally 1 bit" in
struct pt_regs. orig_r8 is the best place to do this, however given the
way it is encoded currently, we can't add anything simplistically.

Current orig_r8:
* syscalls   -> 1 to NR_SYSCALLS
* Exceptions -> NR_SYSCALLS + 1
* Break-point-> NR_SYSCALLS + 2

In new scheme it is a bit-field
* lower short word contains the  exact event type (and a new bit to represent
   restart semantics : if syscall was already / can't be restarted)
* upper short word optionally containing the syscall num - needed by
  likes of tracehooks etc

This patch only changes how orig_r8 is organised and nothing should
change behaviourily.

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
Cc: Al Viro <viro@...IV.linux.org.uk>
---
 arch/arc/include/asm/entry.h  |   29 +++++++++++++++++------------
 arch/arc/include/asm/ptrace.h |   15 +++++++++++----
 arch/arc/kernel/entry.S       |    4 ++--
 3 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 6b42bf5..d72995b 100644
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -343,18 +343,12 @@
  *-------------------------------------------------------------*/
 .macro SAVE_ALL_EXCEPTION   marker
 
+	st      \marker, [sp, 8]
+	st      r0, [sp, 4]    /* orig_r0, needed only for sys calls */
+
 	/* Restore r9 used to code the early prologue */
 	EXCPN_PROLOG_RESTORE_REG  r9
 
-	/* Save the complete regfile now */
-
-	/* orig_r8 marker:
-	 * syscalls   -> 1 to NR_SYSCALLS
-	 * Exceptions -> NR_SYSCALLS + 1
-	 * Break-point-> NR_SYSCALLS + 2
-	 */
-	st      \marker, [sp, 8]
-	st      r0, [sp, 4]    /* orig_r0, needed only for sys calls */
 	SAVE_CALLER_SAVED
 	st.a    r26, [sp, -4]   /* gp */
 	st.a    fp, [sp, -4]
@@ -384,14 +378,25 @@
  * Save scratch regs for exceptions
  *-------------------------------------------------------------*/
 .macro SAVE_ALL_SYS
-	SAVE_ALL_EXCEPTION  (NR_syscalls + 1)
+	SAVE_ALL_EXCEPTION  orig_r8_IS_EXCPN
 .endm
 
 /*--------------------------------------------------------------
  * Save scratch regs for sys calls
  *-------------------------------------------------------------*/
 .macro SAVE_ALL_TRAP
-	SAVE_ALL_EXCEPTION  r8
+	/*
+	 * Encode syscall number (r8) in upper short word of event type (r9)
+	 * (r9 is already clobbered when we land here)
+	 */
+#ifndef CONFIG_CPU_BIG_ENDIAN
+	lsl  r9, r8, 16
+	or   r9, r9, orig_r8_IS_SCALL
+#else
+	lsl  r9, orig_r8_IS_SCALL, 16
+	or   r9, r9, r8
+#endif
+	SAVE_ALL_EXCEPTION  r9
 .endm
 
 /*--------------------------------------------------------------
@@ -442,7 +447,7 @@
 	ld  r9, [@int1_saved_reg]
 
 	/* now we are ready to save the remaining context :) */
-	st     -1, [sp, 8]    /* orig_r8, -1 for interuppt level one */
+	st      orig_r8_IS_IRQ1, [sp, 8]    /* Event Type */
 	st      0, [sp, 4]    /* orig_r0 , N/A for IRQ */
 	SAVE_CALLER_SAVED
 	st.a    r26, [sp, -4]   /* gp */
diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index 9abbb7c..ddb9ce7 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -81,7 +81,8 @@ struct pt_regs {
 	long r0;
 	long sp;	/* user/kernel sp depending on where we came from  */
 	long orig_r0;
-	long orig_r8;	/*to distinguish bet excp, sys call, int1 or int2 */
+	/*to distinguish bet excp, syscall, irq */
+	unsigned long event_type:16, orig_r8:16;
 };
 
 /* Callee saved registers - need to be saved only when you are scheduled out */
@@ -126,12 +127,18 @@ struct user_regs_struct {
 	sp;			\
 })
 
-/* return 1 if in syscall, 0 if Intr or Exception */
-#define in_syscall(regs) (((regs->orig_r8) >= 0 && \
-			   (regs->orig_r8 <= NR_syscalls)) ? 1 : 0)
+#define in_syscall(regs) (regs->orig_r8 & orig_r8_IS_SCALL)
+#define in_brkpt_trap(regs) (regs->orig_r8 & orig_r8_IS_BRKPT)
 
 #endif /* !__ASSEMBLY__ */
 
+#define orig_r8_IS_SCALL		0x0001
+#define orig_r8_IS_SCALL_RESTARTED	0x0002
+#define orig_r8_IS_BRKPT		0x0004
+#define orig_r8_IS_EXCPN		0x0004
+#define orig_r8_IS_IRQ1			0x0010
+#define orig_r8_IS_IRQ2			0x0020
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASM_PTRACE_H */
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index efaf3de..0324ad1 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -354,8 +354,8 @@ ARC_EXIT EV_Extension
 
 trap_with_param:
 
-	;make sure orig_r8 is a positive value
-	st  NR_syscalls + 2, [sp, PT_orig_r8]
+	; stop_pc info by gdb needs this info
+	st  orig_r8_IS_BRKPT, [sp, PT_orig_r8]
 
 	mov r0, r12
 	lr  r1, [efa]
-- 
1.7.4.1

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