ARISE, OLD DEAD THREAD! Hey, this thread is almost legally allowed to drink alcohol in the United States!

Anyways... Uwe Ludwig stumbled upon this and now I am stumbling on this as well. Even if you code in the proper checks on the return value, you will still get a SEGFAULT. There is something weird with lpthreads and getpwuid (and also getlogin) and I don't quite know what it is. But, yes... the combo of these two will always cause a SEGFAULT before you can even check the return.

Stats:
- Ubuntu 20.04
- gcc version 9.4.0
- x86_64-linux-gnu

In article <e95d3f27-47ad-4ff4-8429-92821ad3e79en@googlegroups.com>,
stryker2k2 <stryker2k2@gmail.com> wrote:
>ARISE, OLD DEAD THREAD! Hey, this thread is almost legally allowed to drink
>alcohol in the United States!
>
>Anyways... Uwe Ludwig stumbled upon this and now I am stumbling on this
>as well. Even if you code in the proper checks on the return value, you
>will still get a SEGFAULT. There is something weird with lpthreads and
>getpwuid (and also getlogin) and I don't quite know what it is. But,
>yes... the combo of these two will always cause a SEGFAULT before you
>can even check the return.
>
>Stats:
>- Ubuntu 20.04
>- gcc version 9.4.0
>- x86_64-linux-gnu

Could you post code & build instructions?

Then we might at least have a chance at understanding what you're talking
about, Willis...

--
The randomly chosen signature file that would have appeared here is more than 4
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in compliance with said RFCs, the actual sig can be found at the following URL:
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On 1/4/2023 11:28 AM, Kenny McCormack wrote:
> In article <e95d3f27-47ad-4ff4-8429-92821ad3e79en@googlegroups.com>,
> stryker2k2 <stryker2k2@gmail.com> wrote:
>> ARISE, OLD DEAD THREAD! Hey, this thread is almost legally allowed to drink
>> alcohol in the United States!
>>
>> Anyways... Uwe Ludwig stumbled upon this and now I am stumbling on this
>> as well. Even if you code in the proper checks on the return value, you
>> will still get a SEGFAULT. There is something weird with lpthreads and
>> getpwuid (and also getlogin) and I don't quite know what it is. But,
>> yes... the combo of these two will always cause a SEGFAULT before you
>> can even check the return.
>>
>> Stats:
>> - Ubuntu 20.04
>> - gcc version 9.4.0
>> - x86_64-linux-gnu
>
> Could you post code & build instructions?
>
> Then we might at least have a chance at understanding what you're talking
> about, Willis...
>

Mar 5, 2003, 11:49:55 AM

https://groups.google.com/g/comp.unix.programmer/c/hs23vL73-y0

Paul

Paul <nospam@needed.invalid> writes:
> On 1/4/2023 11:28 AM, Kenny McCormack wrote:
>> stryker2k2 <stryker2k2@gmail.com> wrote:
>>> ARISE, OLD DEAD THREAD! Hey, this thread is almost legally allowed to drink
>>> alcohol in the United States!
>>>
>>> Anyways... Uwe Ludwig stumbled upon this and now I am stumbling on this
>>> as well. Even if you code in the proper checks on the return value, you
>>> will still get a SEGFAULT. There is something weird with lpthreads and
>>> getpwuid (and also getlogin) and I don't quite know what it is. But,
>>> yes... the combo of these two will always cause a SEGFAULT before you
>>> can even check the return.
>>>
>>> Stats:
>>> - Ubuntu 20.04
>>> - gcc version 9.4.0
>>> - x86_64-linux-gnu
>> Could you post code & build instructions?
>> Then we might at least have a chance at understanding what you're
>> talking
>> about, Willis...
>
> Mar 5, 2003, 11:49:55 AM
>
> https://groups.google.com/g/comp.unix.programmer/c/hs23vL73-y0

The program there doesn’t have “the proper checks on the return value”,
so it’s presumably not what you’re actually running. Also, -lpthreads
does not exist; the library is -lpthread. So we don’t yet have the build
commands you used, either. Obviously, nobody can debug code that you’ve
not shared.

I would suggest using gdb or valgrind to identify where your version
crashes.

--
https://www.greenend.org.uk/rjk/

Paul <nospam@needed.invalid> writes:

> On 1/4/2023 11:28 AM, Kenny McCormack wrote:
>> In article <e95d3f27-47ad-4ff4-8429-92821ad3e79en@googlegroups.com>,
>> stryker2k2 <stryker2k2@gmail.com> wrote:
>>> ARISE, OLD DEAD THREAD! Hey, this thread is almost legally allowed to drink
>>> alcohol in the United States!
>>>
>>> Anyways... Uwe Ludwig stumbled upon this and now I am stumbling on this
>>> as well. Even if you code in the proper checks on the return value, you
>>> will still get a SEGFAULT. There is something weird with lpthreads and
>>> getpwuid (and also getlogin) and I don't quite know what it is. But,
>>> yes... the combo of these two will always cause a SEGFAULT before you
>>> can even check the return.
>>>
>>> Stats:
>>> - Ubuntu 20.04
>>> - gcc version 9.4.0
>>> - x86_64-linux-gnu
>>
>> Could you post code & build instructions?
>> Then we might at least have a chance at understanding what you're talking
>> about, Willis...
>
> Mar 5, 2003, 11:49:55 AM
>
> https://groups.google.com/g/comp.unix.programmer/c/hs23vL73-y0

That program, with the undefined behaviour removed, but the curious
verbose style kept, is

#include <pwd.h>
#include <unistd.h>
#include <stdio.h>

char *a;

char *getuser(void)
{
char *username;
struct passwd *info;
info = getpwuid(getuid());
username = info->pw_name;
return username;
}

int main(void)
{
a = getuser();
printf(a);
printf("\n");
}

which compiles and runs fine on my system, with either the -pthread or
-lpthread option. Of course, since threads are not used, the linker may
simply be omitting the code that caused the problem 19 years ago.

The old post refers to -lpthreads (with and s) and my Ubuntu and gcc are
newer.

--
Ben.

Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>Paul <nospam@needed.invalid> writes:
>
>> On 1/4/2023 11:28 AM, Kenny McCormack wrote:
>>> In article <e95d3f27-47ad-4ff4-8429-92821ad3e79en@googlegroups.com>,
>>> stryker2k2 <stryker2k2@gmail.com> wrote:
>>>> ARISE, OLD DEAD THREAD! Hey, this thread is almost legally allowed to drink
>>>> alcohol in the United States!
>>>>
>>>> Anyways... Uwe Ludwig stumbled upon this and now I am stumbling on this
>>>> as well. Even if you code in the proper checks on the return value, you
>>>> will still get a SEGFAULT. There is something weird with lpthreads and
>>>> getpwuid (and also getlogin) and I don't quite know what it is. But,
>>>> yes... the combo of these two will always cause a SEGFAULT before you
>>>> can even check the return.
>>>>
>>>> Stats:
>>>> - Ubuntu 20.04
>>>> - gcc version 9.4.0
>>>> - x86_64-linux-gnu
>>>
>>> Could you post code & build instructions?
>>> Then we might at least have a chance at understanding what you're talking
>>> about, Willis...
>>
>> Mar 5, 2003, 11:49:55 AM
>>
>> https://groups.google.com/g/comp.unix.programmer/c/hs23vL73-y0
>
>That program, with the undefined behaviour removed, but the curious
>verbose style kept, is
>
> #include <pwd.h>
> #include <unistd.h>
> #include <stdio.h>
>
> char *a;
>
> char *getuser(void)
> {
> char *username;
> struct passwd *info;
> info = getpwuid(getuid());
> username = info->pw_name;
> return username;
> }
>
> int main(void)
> {
> a = getuser();
> printf(a);
> printf("\n");
> }
>
>which compiles and runs fine on my system, with either the -pthread or
>-lpthread option. Of course, since threads are not used, the linker may
>simply be omitting the code that caused the problem 19 years ago.
>
>The old post refers to -lpthreads (with and s) and my Ubuntu and gcc are
>newer.

The code will fail if there is no password file entry matching
the current uid.

scott@slp53.sl.home (Scott Lurndal) writes:

> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>Paul <nospam@needed.invalid> writes:
>>
>>> On 1/4/2023 11:28 AM, Kenny McCormack wrote:
>>>> In article <e95d3f27-47ad-4ff4-8429-92821ad3e79en@googlegroups.com>,
>>>> stryker2k2 <stryker2k2@gmail.com> wrote:
>>>>> ARISE, OLD DEAD THREAD! Hey, this thread is almost legally allowed to drink
>>>>> alcohol in the United States!
>>>>>
>>>>> Anyways... Uwe Ludwig stumbled upon this and now I am stumbling on this
>>>>> as well. Even if you code in the proper checks on the return value, you
>>>>> will still get a SEGFAULT. There is something weird with lpthreads and
>>>>> getpwuid (and also getlogin) and I don't quite know what it is. But,
>>>>> yes... the combo of these two will always cause a SEGFAULT before you
>>>>> can even check the return.
>>>>>
>>>>> Stats:
>>>>> - Ubuntu 20.04
>>>>> - gcc version 9.4.0
>>>>> - x86_64-linux-gnu
>>>>
>>>> Could you post code & build instructions?
>>>> Then we might at least have a chance at understanding what you're talking
>>>> about, Willis...
>>>
>>> Mar 5, 2003, 11:49:55 AM
>>>
>>> https://groups.google.com/g/comp.unix.programmer/c/hs23vL73-y0
>>
>>That program, with the undefined behaviour removed, but the curious
>>verbose style kept, is
>>
>> #include <pwd.h>
>> #include <unistd.h>
>> #include <stdio.h>
>>
>> char *a;
>>
>> char *getuser(void)
>> {
>> char *username;
>> struct passwd *info;
>> info = getpwuid(getuid());
>> username = info->pw_name;
>> return username;
>> }
>>
>> int main(void)
>> {
>> a = getuser();
>> printf(a);
>> printf("\n");
>> }
>>
>>which compiles and runs fine on my system, with either the -pthread or
>>-lpthread option. Of course, since threads are not used, the linker may
>>simply be omitting the code that caused the problem 19 years ago.
>>
>>The old post refers to -lpthreads (with and s) and my Ubuntu and gcc are
>>newer.
>
> The code will fail if there is no password file entry matching
> the current uid.

Sure, but if that's what the OP is observing, then I can't see the
connection to the pthread library.

--
Ben.