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From: Roland McGrath <roland@redhat.com>
To: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: [PATCH 2/2] x86_64 ptrace vs -ENOSYS
Date: Sun, 16 Mar 2008 21:59:11 -0700 (PDT)	[thread overview]
Message-ID: <20080317045911.D241E26F995@magilla.localdomain> (raw)
In-Reply-To: Roland McGrath's message of  Sunday, 16 March 2008 21:57:41 -0700 <20080317045741.2F6A526F995@magilla.localdomain>


When we're stopped at syscall entry tracing, ptrace can change the %rax
value from -ENOSYS to something else.  If no system call is actually made
because the syscall number (now in orig_rax) is bad, then we now always
reset %rax to -ENOSYS again.

This changes it to leave the return value alone after entry tracing.
That way, the %rax value set by ptrace is there to be seen in user mode
(or in syscall exit tracing).  This is consistent with what the 32-bit
kernel does.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
 arch/x86/kernel/entry_64.S |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index c20c9e7..556a8df 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -319,19 +319,17 @@ badsys:
 	/* Do syscall tracing */
 tracesys:			 
 	SAVE_REST
-	movq $-ENOSYS,RAX(%rsp)
+	movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
 	FIXUP_TOP_OF_STACK %rdi
 	movq %rsp,%rdi
 	call syscall_trace_enter
 	LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
 	RESTORE_REST
 	cmpq $__NR_syscall_max,%rax
-	movq $-ENOSYS,%rcx
-	cmova %rcx,%rax
-	ja  1f
+	ja   int_ret_from_sys_call	/* RAX(%rsp) set to -ENOSYS above */
 	movq %r10,%rcx	/* fixup for C */
 	call *sys_call_table(,%rax,8)
-1:	movq %rax,RAX-ARGOFFSET(%rsp)
+	movq %rax,RAX-ARGOFFSET(%rsp)
 	/* Use IRET because user could have changed frame */
 		
 /* 

  reply	other threads:[~2008-03-17  4:59 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-17  4:57 [PATCH 1/2] x86_64 ia32 " Roland McGrath
2008-03-17  4:59 ` Roland McGrath [this message]
2008-03-19  1:23 ` [PATCH] x86_64 ia32 ptrace vs -ENOSYS sysenter/syscall Roland McGrath
2008-03-19 22:17 ` [PATCH 1/2] x86_64 ia32 ptrace vs -ENOSYS Andrew Morton
2008-03-19 23:36   ` Roland McGrath
2008-03-21 10:33     ` Ingo Molnar

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