2 files changed, 33 insertions, 4 deletions

diff --git a/arch/um/sys-i386/ptrace.c b/arch/um/sys-i386/ptrace.c
index e839ce65ad2..8032a105949 100644
--- a/arch/um/sys-i386/ptrace.c
+++ b/arch/um/sys-i386/ptrace.c
@@ -6,6 +6,7 @@
 #include <linux/config.h>
 #include <linux/compiler.h>
 #include "linux/sched.h"
+#include "linux/mm.h"
 #include "asm/elf.h"
 #include "asm/ptrace.h"
 #include "asm/uaccess.h"
@@ -26,9 +27,17 @@ int is_syscall(unsigned long addr)
 
         n = copy_from_user(&instr, (void __user *) addr, sizeof(instr));
         if(n){
-                printk("is_syscall : failed to read instruction from 0x%lx\n",
-                       addr);
-                return(0);
+                /* access_process_vm() grants access to vsyscall and stub,
+                 * while copy_from_user doesn't. Maybe access_process_vm is
+                 * slow, but that doesn't matter, since it will be called only
+                 * in case of singlestepping, if copy_from_user failed.
+                 */
+                n = access_process_vm(current, addr, &instr, sizeof(instr), 0);
+                if(n != sizeof(instr)) {
+                        printk("is_syscall : failed to read instruction from "
+                               "0x%lx\n", addr);
+                        return(1);
+                }
         }
         /* int 0x80 or sysenter */
         return((instr == 0x80cd) || (instr == 0x340f));
diff --git a/arch/um/sys-x86_64/ptrace.c b/arch/um/sys-x86_64/ptrace.c
index 74eee5c7c6d..147bbf05cbc 100644
--- a/arch/um/sys-x86_64/ptrace.c
+++ b/arch/um/sys-x86_64/ptrace.c
@@ -8,6 +8,7 @@
 #include <asm/ptrace.h>
 #include <linux/sched.h>
 #include <linux/errno.h>
+#include <linux/mm.h>
 #include <asm/uaccess.h>
 #include <asm/elf.h>
 
@@ -136,9 +137,28 @@ void arch_switch(void)
 */
 }
 
+/* XXX Mostly copied from sys-i386 */
 int is_syscall(unsigned long addr)
 {
-        panic("is_syscall");
+        unsigned short instr;
+        int n;
+
+        n = copy_from_user(&instr, (void __user *) addr, sizeof(instr));
+        if(n){
+                /* access_process_vm() grants access to vsyscall and stub,
+                 * while copy_from_user doesn't. Maybe access_process_vm is
+                 * slow, but that doesn't matter, since it will be called only
+                 * in case of singlestepping, if copy_from_user failed.
+                 */
+                n = access_process_vm(current, addr, &instr, sizeof(instr), 0);
+                if(n != sizeof(instr)) {
+                        printk("is_syscall : failed to read instruction from "
+                               "0x%lx\n", addr);
+                        return(1);
+                }
+        }
+        /* sysenter */
+        return(instr == 0x050f);
 }
 
 int dump_fpu(struct pt_regs *regs, elf_fpregset_t *fpu )