Package: libc6 Version: 2.21-9 User: [email protected] Usertags: m68k
Hi,
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.
Regards,
James
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