svn commit: r304928 - in head/lib/libc: amd64/sys i386/sys sys

[Konstantin Belousov]

Author: kib
Date: Sat Aug 27 23:03:23 2016
New Revision: 304928
URL: https://svnweb.freebsd.org/changeset/base/304928

Log:
  Do not obliterate errno value in the main thread during ptrace(2) call on x86.
  
  Since ptrace(2) syscall can return -1 for non-error situations, libc
  wrappers set errno to 0 before performing the syscall, as the service
  to the caller.  On both i386 and amd64, the errno symbol was directly
  referenced, which only works correctly in single-threaded process.
  
  Change assembler wrappers for ptrace(2) to get current thread errno
  location by calling __error().  Allow __error interposing, as
  currently allowed in cerror().
  
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/lib/libc/amd64/sys/ptrace.S
  head/lib/libc/i386/sys/ptrace.S
  head/lib/libc/sys/ptrace.2

Modified: head/lib/libc/amd64/sys/ptrace.S
==============================================================================
--- head/lib/libc/amd64/sys/ptrace.S	Sat Aug 27 22:43:41 2016	(r304927)
+++ head/lib/libc/amd64/sys/ptrace.S	Sat Aug 27 23:03:23 2016	(r304928)
@@ -38,14 +38,16 @@ __FBSDID("$FreeBSD$");
 
 #include "SYS.h"
 
+	.globl	CNAME(__error)
+	.type	CNAME(__error), at function
+
 ENTRY(ptrace)
-	xorl	%eax,%eax
 #ifdef PIC
-	movq	PIC_GOT(CNAME(errno)),%r8
-	movl	%eax,(%r8)
+	callq	PIC_PLT(CNAME(__error))
 #else
-	movl	%eax,CNAME(errno)(%rip)
+	callq	CNAME(__error)
 #endif
+	movl	$0,(%rax)
 	mov	$SYS_ptrace,%eax
 	KERNCALL
 	jb	HIDENAME(cerror)

Modified: head/lib/libc/i386/sys/ptrace.S
==============================================================================
--- head/lib/libc/i386/sys/ptrace.S	Sat Aug 27 22:43:41 2016	(r304927)
+++ head/lib/libc/i386/sys/ptrace.S	Sat Aug 27 23:03:23 2016	(r304928)
@@ -38,16 +38,18 @@ __FBSDID("$FreeBSD$");
 
 #include "SYS.h"
 
+	.globl	CNAME(__error)
+	.type	CNAME(__error), at function
+
 ENTRY(ptrace)
-	xorl	%eax,%eax
 #ifdef PIC
-        PIC_PROLOGUE
-        movl    PIC_GOT(CNAME(errno)),%edx
-        movl    %eax,(%edx)
-        PIC_EPILOGUE
+	PIC_PROLOGUE
+	call	PIC_PLT(CNAME(__error))
+	PIC_EPILOGUE
 #else
-        movl    %eax,CNAME(errno)
+	call	CNAME(__error)
 #endif
+	movl	$0,(%eax)
 	mov	$SYS_ptrace,%eax
 	KERNCALL
 	jb	HIDENAME(cerror)

Modified: head/lib/libc/sys/ptrace.2
==============================================================================
--- head/lib/libc/sys/ptrace.2	Sat Aug 27 22:43:41 2016	(r304927)
+++ head/lib/libc/sys/ptrace.2	Sat Aug 27 23:03:23 2016	(r304928)
@@ -2,7 +2,7 @@
 .\"	$NetBSD: ptrace.2,v 1.2 1995/02/27 12:35:37 cgd Exp $
 .\"
 .\" This file is in the public domain.
-.Dd July 28, 2016
+.Dd August 28, 2016
 .Dt PTRACE 2
 .Os
 .Sh NAME
@@ -906,7 +906,13 @@ to return
 \-1
 as a non-error value; to disambiguate,
 .Va errno
-can be set to 0 before the call and checked afterwards.
+is set to 0 in the libc wrapper for the
+.Fn ptrace
+system call and
+.Fn ptrace
+callers can reliably check
+.Va errno
+for non-zero value afterwards.
 .Sh ERRORS
 The
 .Fn ptrace