Consider this code:
1202 static fragS * get_frag_for_reloc (fragS *last_frag,
1203 const segment_info_type *seginfo,
1204 const struct reloc_list *r)
1205 {
1206 fragS *f;
1207
1208 for (f = last_frag; f != NULL; f = f->fr_next)
1209 if (f->fr_address <= r->u.b.r.address
1210 && r->u.b.r.address < f->fr_address + f->fr_fix)
1211 return f;
1212
1213 for (f = seginfo->frchainP->frch_root; f != NULL; f = f->fr_next)
1214 if (f->fr_address <= r->u.b.r.address
1215 && r->u.b.r.address < f->fr_address + f->fr_fix)
1216 return f;
1217
1218 for (f = seginfo->frchainP->frch_root; f != NULL; f = f->fr_next)
1219 if (f->fr_address <= r->u.b.r.address
1220 && r->u.b.r.address <= f->fr_address + f->fr_fix)
1221 return f;
1222
1223 as_bad_where (r->file, r->line,
1224 _("reloc not within (fixed part of) section"));
1225 return NULL;
1226 }
This function consists of 3 loops: 1208-1211, 1213 to 1216 and 1218 to 1221.
Lines 1213 - 1216 are ALMOST identical to lines 1218 to 1221. The ONLY
difference that I can see is that the less in line 1215 is replaced by a less
equal in line 1220.
But… why?
This code is searching the fragment that contains a given address in between
the start and end addresses of the frags in question, either in the fragment
list given by last_frag or in the list given by seginfo.
To know if a fragment is OK you should start with the given address and stop
one memory address BEFORE the limit given by fr_address + f->fr_fix. That is
what the first two loops are doing. The third loop repeats the second one and
changes the less to less equal, so if fr_address+fr_fix is one MORE than the
address it will still pass.
Why it is doing that?
If that code is correct, it is obvious that we could merge the second and third
loops and put a <= in t he second one and erase the third one… UNLESS priority
should be given to matches that are less and not less equal, what seems
incomprehensible … to me.
This change was introduced on Aug 18th 2011 by Mr Alan Modra with the rather
terse comment: "(get_frag_for_reloc): New function. ». There are no further
comments in the code at all.
This code is run after all relocations are fixed just before the software
writes them out. The code is in file « write.c » in the gas directory. Note
that this code runs through ALL relocations lists each time for EACH
relocation, so it is quite expensive. In general the list data structure is not
really optimal here but that is another story.
Thanks in advance for your help.
Jacob
