>>>>> Arnaud Charlet writes:
Arnaud> Although I would need to see the entire issue we're trying to solve
under
Arnaud> AIX, since it's not clear at all to me that forcing -mminimal-toc
Arnaud> systematically is a good idea to start with. Could you point to a
detailed
Arnaud> discussion on the AIX issue ?
AIX has a limit on the size of the TOC (similar to ELF GOT). The
TOC provides global PIC addressibility and is used for global variables,
static variables, and constants. The data sections patch will improve
this situation by creating a local pool for constants and static
variables, as IBM XLC has done from its initial implementation.
-mminimal-toc instructs GCC to generate one TOC entry per function
and use a side table for all addressibility in the function, reducing the
size of the TOC to the number of functions in the executable or shared
object, instead of the number of variables and constants. One can
intermix object files compiled with and without the option.
One also can fixup the TOC overflow in the linker, which is
reasonably efficient for a small number of extra entries, but inefficient
for a large overflow.
When Ada builds on AIX, libada contains a very large number of TOC
entries. Even the smallest, simplest executable overflows because the
entire TOC is consumed by libada. Using this option when building libada
compacts the library so that applications encounter TOC overflow less
often.
When the data section patch is merged into GCC, this may not be
necessary, so maybe we should just declare GNU Ada unusable on AIX until
that patch is committed.
David
