38 ms·

All this for the possibility of interposition? Yes, it seems so. The impact is there for this little-known and little-used feature. Instead of optimising for th

by dkarl 15y ago

All this for the possibility of interposition? Yes, it seems so. The impact is there for this little-known and little-used feature. Instead of optimising for the common-case scenario where the symbols are not overridden, the ABI optimises for the corner case. Using LD_PRELOAD isn't so rare and strange that you can propose throwing it out without quantifying its performance cost. I can't recall offhand why I needed it (I would guess Valgrind or Massif) but I've used it several times as a developer. What exactly is the payoff for giving it up? It can't be bigger than the current performance difference between statically and dynamically linked executables, can it?

gioele 15y ago
> All this for the possibility of interposition? Yes, it seems so. The impact is there for this little-known and little-used feature. Instead of optimising for the common-case scenario where the symbols are not overridden, the ABI optimises for the corner case. It also looks like PIE+PIC is required if you want a secure system with ASLR: <http://blog.flameeyes.eu/2009/11/02/the-pie-is-not-exactly-a-lie> http://blog.flameeyes.eu/2009/11/02/the-pie-is-not-exactly-a.... Flameeyes (Gentoo dev) has sent patches to all the main library developer that make sure only the necessary number of symbols is exposed and as much data as possible is marked as read-only. I think this effort is more valuable than proposing a very unlikely ABI change.
- klodolph 15y ago
  Of course, a bunch of this work is sabotaged by stupid default `LDFLAGS` you get if you use `pkg-config` and some package (like `gmodule`) throws random stuff in there like `-Wl,--export-dynamic` which is just totally unnecessary for at least 99% of executables which only ever used `gmodule` indirectly in the first place...
ars 15y ago
LD_PRELOAD is used by fakeroot, artsdsp, esddsp, alsadsp to name some of the most popular programs that use it.
- forgotusername 15y ago
  Only for overriding parts of libc, which already cannot be 'unexported'. The article's main beef is with internal program symbols also being made indirect (AIUI a patch adding a new visibility option was landed in gcc years ago that more or less automatically fixed this up, but I may be wrong) Edit: rushing out the door here, last sentence was referring to this: http://gcc.gnu.org/wiki/Visibility http://gcc.gnu.org/wiki/Visibility

by dkarl 15y ago

gioele 15y ago

> All this for the possibility of interposition? Yes, it seems so. The impact is there for this little-known and little-used feature. Instead of optimising for the common-case scenario where the symbols are not overridden, the ABI optimises for the corner case. It also looks like PIE+PIC is required if you want a secure system with ASLR: <http://blog.flameeyes.eu/2009/11/02/the-pie-is-not-exactly-a-lie> http://blog.flameeyes.eu/2009/11/02/the-pie-is-not-exactly-a.... Flameeyes (Gentoo dev) has sent patches to all the main library developer that make sure only the necessary number of symbols is exposed and as much data as possible is marked as read-only. I think this effort is more valuable than proposing a very unlikely ABI change.

klodolph 15y ago
Of course, a bunch of this work is sabotaged by stupid default `LDFLAGS` you get if you use `pkg-config` and some package (like `gmodule`) throws random stuff in there like `-Wl,--export-dynamic` which is just totally unnecessary for at least 99% of executables which only ever used `gmodule` indirectly in the first place...

ars 15y ago

LD_PRELOAD is used by fakeroot, artsdsp, esddsp, alsadsp to name some of the most popular programs that use it.

forgotusername 15y ago
Only for overriding parts of libc, which already cannot be 'unexported'. The article's main beef is with internal program symbols also being made indirect (AIUI a patch adding a new visibility option was landed in gcc years ago that more or less automatically fixed this up, but I may be wrong) Edit: rushing out the door here, last sentence was referring to this: http://gcc.gnu.org/wiki/Visibility http://gcc.gnu.org/wiki/Visibility