Your message dated Thu, 2 Jan 2020 21:42:26 +0100
with message-id <>
and subject line Re: Bug#868076: libc6: gethostbyname assertion failure on m68k
has caused the Debian Bug report #868076,
regarding Assertion failure in gethostbyname 
to be marked as done.

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--- Begin Message ---
Package: libc6
Version: 2.21-9
Usertags: m68k

Backstory: I maintain polyml, and was porting it to m68k; when running the test 
suite, I received an assertion failure in glibc in a call to gethostbyname.

It seems gethostbyname is broken, failing for me with 
“nss_files/files-hosts.c:218: _nss_files_gethostbyname3_r: Assertion 
`(bufferend - (char *) 0) % sizeof (char *) == 0' failed.” This can be 
reproduced with the following simple program:

    #include <stdio.h>
    #include <netdb.h>

    int main(int argc, char **argv) {
        struct hostent *h = gethostbyname("localhost");
        printf("name: %s\n", h->h_name);
        return 0;

Delving inside glibc, _nss_files_gethostbyname3_r expects result->h_aliases to 
be aligned to sizeof(char *), as can be seen in the assert (bufferend points to 
an element in result->h_aliases, and each element is a char *). Provided this 
is true when the function is called, it seems to correctly maintain the 
invariant by rounding up bufferend when necessary.

However, the initial value of result->h_aliases is not aligned to sizeof(char 
*). Instead, it is assigned in parse_list (nss_files/files-parse.c:245) and 
aligned to __alignof__(char *). On many architectures, these are the same, but 
on m68k, __alignof__(char *) == 2, but sizeof(char *) == 4. There may be 
environments where result->h_aliases happens to be aligned to sizeof(char *) by 
chance, but that is most certainly not the case on mine (latest unstable 
running in ARAnyM).

I don’t know why bufferend is required to be aligned to sizeof(char *), and 
believe that imposing __alignof__(char *) in _nss_files_gethostbyname3_r 
instead would suffice. Alternatively, parse_list could choose MAX(sizeof(char 
*), __alignof__(char *)) as the alignment. Either way, the implementation as a 
whole is currently broken.


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--- Begin Message ---
Version: 2.27-1

On 2017-07-11 21:21, James Clarke wrote:
> Package: libc6
> Version: 2.24-12
> Tags: upstream patch
> Forwarded:
> User:
> Usertags: m68k
> X-Debbugs-Cc:
> Hi,
> On m68k, gethostbyname can sometimes cause an assertion failure:
> > "nss_files/files-hosts.c:218: _nss_files_gethostbyname3_r: Assertion 
> > `(bufferend - (char *) 0) % sizeof (char *) == 0' failed."

According to upstream this problem has been fixed in version 2.27-1. I
am therefore closing the bug with that version.

Aurelien Jarno                          GPG: 4096R/1DDD8C9B       

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