On 04/27/2017 09:41 PM, Mark Wielaard wrote: > On Thu, Apr 20, 2017 at 04:54:26PM +0200, Ulf Hermann wrote: >> At least one test (dwfl-addr-sect) depends on the order of elf sections >> with equal addresses. This is not guaranteed by the code. Compare also >> by end address and name to tell entries apart. > > O, interesting find. If the start addresses match the order depends on > the specific qsort algorithm. So you need a real tie breaker. > > I think it is simpler and more predictable if we just take the section > number into account. It seem to have the added benefit that it provide > the same ordering as before with the glibc qsort, so no testcases need > to be adjusted. Does the following work for you? > > diff --git a/libdwfl/derelocate.c b/libdwfl/derelocate.c > index 439a24e..0d10672 100644 > --- a/libdwfl/derelocate.c > +++ b/libdwfl/derelocate.c > @@ -63,7 +63,10 @@ compare_secrefs (const void *a, const void *b) > if ((*p1)->start > (*p2)->start) > return 1; > > - return 0; > + /* Same start address, then just compare which section came first. */ > + size_t n1 = elf_ndxscn ((*p1)->scn); > + size_t n2 = elf_ndxscn ((*p2)->scn); > + return n1 - n2;
I would inline the whole thing to return elf_ndxscn (p1->scn) - elf_ndxscn (p2->scn); There is no point in forcing the compiler to keep the intermediate numbers as (signed) size_t. Also, I would still keep the check for p1->end and p2->end before this. If we have a section of size 0, and another one of size > 0 starting at the same place, we want them to be sorted by end address. The zero-sized section should be squeezed in before the one that actually has a size, not after it. Ulf
