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Subject[PATCH] 2-ptrace_multi
From
ptmulti kernel patch inserts a new useful option for ptrace() call, 
adding a new request type to ptrace() syscall.

With PTRACE_MULTI option you can send multiple ptrace requests with a
single system call: commonly a process that uses ptrace() needs
several PTRACE_PEEKDATA for getting some useful, even small pieces of data.
It is useful for these programs to run several ptrace
operations while limiting the number of context switches.

Ptrace-multi gets a "struct ptrace_multi" array (together with its
number of elements). It is in this way similar to the management of buffers
for readv or writev.
Each "struct ptrace_multi" specifies a single request of normal type of
ptrace. So you have can join several requests into a requests array that will
be passed through the "void* addr" parameter (the third) of ptrace().
The last argument specify the numbers of request to be accomplished by ptrace.

While normal ptrace requests can get a word at a time, we have added some other
request for simplify the interface between kernel
and applications that use ptrace(); these requests can get from user space more
than one word at a time:
- PTRACE_PEEKCHARDATA and PTRACE_POKECHARDATA is used for transferring general
data, like structure, buffer, and so on...
- PTRACE_PEEKSTRINGDATA get strings from user space (it relies on
access_process_vm_user patch) and it check that data returned is a well formed
string (null-terminated)

Debuggers and virtual machines (like User Mode Linux) and many other
applications that are based on ptrace can get great
performance improvements by PTRACE_MULTI: the number of system
calls (and context switches) decreases significantly.

This patch is architecture independent.

Signed-off-by: renzo davoli <renzo@cs.unibo.it>

diff -Naur linux-2.6.17-rc1/include/linux/ptrace.h linux-2.6.17-rc1-ptmulti/include/linux/ptrace.h
--- linux-2.6.17-rc1/include/linux/ptrace.h 2006-04-04 16:18:55.000000000 +0200
+++ linux-2.6.17-rc1-ptmulti/include/linux/ptrace.h 2006-04-04 16:17:30.000000000 +0200
@@ -27,6 +27,18 @@
#define PTRACE_GETSIGINFO 0x4202
#define PTRACE_SETSIGINFO 0x4203

+#define PTRACE_MULTI 0x4300
+#define PTRACE_PEEKCHARDATA 0x4301
+#define PTRACE_POKECHARDATA 0x4302
+#define PTRACE_PEEKSTRINGDATA 0x4303
+
+struct ptrace_multi {
+ long request;
+ long addr;
+ void *localaddr;
+ long length;
+};
+
/* options set using PTRACE_SETOPTIONS */
#define PTRACE_O_TRACESYSGOOD 0x00000001
#define PTRACE_O_TRACEFORK 0x00000002
diff -Naur linux-2.6.17-rc1/kernel/ptrace.c linux-2.6.17-rc1-ptmulti/kernel/ptrace.c
--- linux-2.6.17-rc1/kernel/ptrace.c 2006-04-04 16:18:55.000000000 +0200
+++ linux-2.6.17-rc1-ptmulti/kernel/ptrace.c 2006-04-04 16:17:30.000000000 +0200
@@ -2,6 +2,7 @@
* linux/kernel/ptrace.c
*
* (C) Copyright 1999 Linus Torvalds
+ * PTRACE_MULTI support 2006 Renzo Davoli
*
* Common interfaces for "ptrace()" which we do not want
* to continually duplicate across every architecture.
@@ -503,6 +504,53 @@
return child;
}

+static int multi_ptrace(struct task_struct *child, long request, long addr, long size)
+{
+ int i, ret;
+ long j;
+ ret=0;
+ if (!access_ok(VERIFY_READ, addr,size*sizeof(struct ptrace_multi))) {
+ ret = -EIO;
+ goto out_multi_ptrace;
+ }
+ for (i=0; i<size && ret==0; i++, addr+=sizeof(struct ptrace_multi)) {
+ unsigned long len;
+ struct ptrace_multi __user pm ;
+ __copy_from_user(&pm, (struct ptrace_multi __user *)addr, sizeof(struct ptrace_multi));
+ len = pm.length;
+ switch ( pm.request){
+ case PTRACE_PEEKTEXT:
+ case PTRACE_PEEKDATA:
+ case PTRACE_PEEKUSR:
+ if (len <= 0) len=1;
+ for (j=0; j<len && ret==0; j++)
+ ret=arch_ptrace(child, pm.request, (long) (pm.addr) + j*sizeof(long), (long) (pm.localaddr) + j*sizeof(long));
+ break;
+ case PTRACE_POKETEXT:
+ case PTRACE_POKEDATA:
+ case PTRACE_POKEUSR:
+ if (len <= 0) len=1;
+ for (j=0; j<len && ret==0; j++)
+ ret=arch_ptrace(child, pm.request, (long) (pm.addr) + j*sizeof(long), *(((long *) (pm.localaddr)) + j));
+ break;
+ case PTRACE_PEEKCHARDATA:
+ ret = ptrace_readdata(child, pm.addr, pm.localaddr, len);
+ break;
+ case PTRACE_POKECHARDATA:
+ ret = ptrace_writedata(child, pm.localaddr, pm.addr, len);
+ break;
+ case PTRACE_PEEKSTRINGDATA:
+ ret = ptrace_readstringdata(child, pm.addr, pm.localaddr, len);
+ break;
+ default:
+ ret=arch_ptrace(child, pm.request, (long) (pm.addr), (long) (pm.localaddr));
+ break;
+ }
+ }
+ out_multi_ptrace:
+ return ret;
+}
+
#ifndef __ARCH_SYS_PTRACE
asmlinkage long sys_ptrace(long request, long pid, long addr, long data)
{
@@ -533,6 +581,9 @@
if (ret < 0)
goto out_put_task_struct;

+ if (request == PTRACE_MULTI)
+ ret = multi_ptrace(child, request, addr, data);
+ else
ret = arch_ptrace(child, request, addr, data);
if (ret < 0)
goto out_put_task_struct;
-
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