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Re: Build failure with probe patch
- From: jose dot marchesi at oracle dot com (Jose E. Marchesi)
- To: Pedro Alves <palves at redhat dot com>
- Cc: Steve Ellcey <sellcey at imgtec dot com>, Sergio Durigan Junior <sergiodj at redhat dot com>, gdb-patches at sourceware dot org
- Date: Thu, 19 Feb 2015 21:17:05 +0100
- Subject: Re: Build failure with probe patch
- Authentication-results: sourceware.org; auth=none
- References: <bac100bc-73de-4bf6-86b5-912ad6887c5a at BAMAIL02 dot ba dot imgtec dot org> <87wq3ercw0 dot fsf at redhat dot com> <1424306916 dot 27855 dot 115 dot camel at ubuntu-sellcey> <87r3tl7uwz dot fsf at oracle dot com> <54E6150B dot 9060808 at redhat dot com> <87vbix3iqm dot fsf at oracle dot com> <54E62BCB dot 80600 at redhat dot com>
> Yes, but not the other way around... it is not allowed to alias a
> character type with a non-character type like in the following call to
> dtrace_process_dof:
Ah, right.
> gdb_byte *buf;
> [...]
> dtrace_process_dof (sect, objfile, probesp, (struct dtrace_dof_hdr *) buf);
Hmm, still, but I think this may be alright.
gdb_bfd_map_section and bfd_get_full_section_contents return
allocated objects, which have no declared type to begin with
(C99 6.5/6, footnote 75).
Then per C99 6.5/6, since the allocated object is never written
through an lvalue with a type that is not a character type, then
the effective type of the object is "simply the type of the
lvalue used for the access."
So it seems to me that casting to struct dtrace_dof_hdr * and then
reading from that lvalue is OK: from that point on, the object
pointed at by BUF has effective type struct dtrace_dof_hdr.
Good point! Yes, I agree. Both bfd_byte and gdb_byte are character
types, so the object returned by either bfd_malloc_and_get_section or
gdb_bfd_map_section must retain the property of not having a declared
type.