Debian Bug report logs - #553189
mprotect library call shows 5 arguments instead of 3

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: Andrew Yourtchenko <ayourtch@cisco.com>

To: submit@bugs.debian.org

Subject: mprotect library call shows 5 arguments instead of 3

Date: Thu, 29 Oct 2009 13:55:46 +0100 (CET)

Package: ltrace
Version: 0.5.1-2ubuntu1
Severity: minor

I also tested this on 0.5.2. Dummy testcase file foo.c:

#include <sys/mman.h>
int main (int argc, char *argv[])
{
 mprotect ((void*)0xdeadbeef, 4096, PROT_NONE);
 return 0;
}

Running it under ltrace gives:

$ ltrace ./foo
__libc_start_main(0x80483c4, 1, 0xbfa33894, 0x8048410, 0x8048400 <unfinished ...>
mprotect(0xdeadbeef, 4096, 0, 0x8048429, 0xb7f25870) = -1
+++ exited (status 0) +++
$

Based on my analysis, the behaviour is "technically" correct, because 
only the syscall's signature is in the config:

$ grep mprotect /etc/ltrace.conf
int   SYS_mprotect(addr,int,int);
$

And by default the number of arguments that ltrace prints for the 
functions without the signatures is 5.

Indeed "ltrace -S ./foo" prints the syscall itself correctly:

[lots of other syscalls]
__libc_start_main(0x80483c4, 1, 0xbfb799d4, 0x8048410, 0x8048400 
<unfinished ...>
mprotect(0xdeadbeef, 4096, 0, 0x8048429, 0xb7f6d870 <unfinished ...>
SYS_mprotect(0xdeadbeef, 4096, 0)                = -22
<... mprotect resumed> )                         = -1
SYS_exit_group(0 <no return ...>
+++ exited (status 0) +++

Adding the type signature into the config file for the mprotect same as 
SYS_mprotect corrects the output. I suggest this addition is made in the 
/etc/ltrace.conf

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