Hello Joel,
On 18/05/2021 23:40, Joel Sherrill wrote:
Hi
In working with Alex to reduce the minimum on his new BSP, we noticed
that it is easy for a BSP to accidentally trip up and end up with a
minimum.exe that is as much as 2x over what it should be. I have looked
at a few BSPs and seen a handful of issues so far. I have patches
pending for some. This particular issue I think indicates a dependency
path that is too heavy. I spotted this on powerpc/psim and likely
impacts a number of BSPs. I made two minor changes reduced the size of
minimum.exe as shown below
text data bss dec hex filename
66616 11848 268356980 268435444 ffffff4 minimum.exe
45064 5884 268384476 268435424 fffffe0 minimum.exe
FWIW That 45K is larger than the ARM or MIPS BSPs I looked at but seems
reasonable due to all the PPC helper and IRQ code pulled in.
psim does two things that the arm and mips BSPs I looked at do not. It
uses the powerpc shared sbrk.c and it calls malloc() from its
irq_init.c. malloc() and sbrk() set errno. Commenting out setting errno
in those two methods is what resulted in 21.5K text and 6K data saved.
we have an rtems_malloc() and rtems_calloc() which do not set errno.
I think setting errno doesn't directly add this much code but the
sysinit dependency chain it trips ends up pulling in getreent,
rtems_libio_init, rtems_libio_post_driver (opening /dev/console), open,
atexit(), close(), rtems_filesystem_do_unmount() and a host of other
things. I am not sure of the exact order of the chain but that's the end
result.I do think it starts with getreent though.
Yes, if you use __getreent() with
#define CONFIGURE_DISABLE_NEWLIB_REENTRANCY
then a lot of stuff is pulled in.
If you don't use this option, then a lot of stuff is pulled in by the
Newlib extensions.
It would be nice to call a method that uses errno without automatically
pulling in this much baggage via a long dependency chain.
Alternatively, the BSPs should use a malloc alternative that does not
set errno. And our sbrk is only used in one place so it could simply not
set errno.
Fixing the dependency chain is the preferred solution.
I am not sure how the dependency chain can be fixed with the current
struct _reent approach of Newlib. A modern approach would be to replace
this structure with individual thread-local objects. This would be
technically feasible, however, a lot of work.
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