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Avoid ubsan bug complaining about &p->field

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I reckon it's quite OK to write &p->field in C when p might be NULL,
and lots of old C programmers probably agree with me.  However, ubsan
disagrees and so do some people I respect.  I suspect C++ influence is
to blame for the ubsan behaviour.  See
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92634.  So far no one has
educated me as to why I'm wrong to claim that there isn't anything in
the C standard to say that p->field is always (*p).field.  Note 79
doesn't quite do that because it doesn't cover null pointers.  If
there was such an equivalence then you could claim &p->field has a
null pointer reference when p is NULL, even though no C compiler would
ever dereference p.

Anyway, to silence ubsan I'm going to apply the following though I
prefer to avoid casts when possible.  And I'm using (void *)
deliberately because this is C, not C++!

	* ldlang.c (lang_output_section_find_by_flags): Don't use &p->field
	when p might be NULL.
	* ldelf.c (output_rel_find, ldelf_place_orphan): Likewise.
	(insert_os_after, lang_insert_orphan, lookup_name): Likewise.
	(strip_excluded_output_sections, lang_clear_os_map): Likewise.
	(lang_check, lang_for_each_input_file): Likewise.
	(lang_reset_memory_regions, find_replacements_insert_point): Likewise.
	(find_rescan_insertion, lang_propagate_lma_regions): Likewise.
	(lang_record_phdrs): Likewise.
	* emultempl/alphaelf.em (alpha_after_open): Likewise.
	* emultempl/mmo.em (mmo_place_orphan): Likewise.
	* emultempl/pe.em (gld_${EMULATION_NAME}_place_orphan): Likewise.
	* emultempl/pep.em (gld_${EMULATION_NAME}_place_orphan): Likewise.
	* emultempl/ppc32elf.em (ppc_after_check_relocs): Likewise.
	* emultempl/spuelf.em (spu_before_allocation): Likewise.
	(embedded_spu_file): Likewise.
This commit is contained in:
Alan Modra
2019-11-26 16:49:44 +10:30
parent 100b122fc1
commit 8ce18f9cdf
9 changed files with 44 additions and 25 deletions
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4
ld/emultempl/spuelf.em
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@@ -290,7 +290,7 @@ spu_before_allocation (void)
}
/* Ensure alignment of overlay sections is sufficient. */
for (os = &lang_os_list.head->output_section_statement;
for (os = (void *) lang_os_list.head;
os != NULL;
os = os->next)
if (os->bfd_section != NULL
@@ -512,7 +512,7 @@ embedded_spu_file (lang_input_statement_type *entry, const char *flags)
return FALSE;
close (fd);
for (search = &input_file_chain.head->input_statement;
for (search = (void *) input_file_chain.head;
search != NULL;
search = search->next_real_file)
if (search->filename != NULL)