package/collectd: Specify correct FP layout for PowerPC

PowerPC stores floating point as big endian, so, in order for 'network' plugin to work correctly (and potentially any user of htond() in collectd's codebase), --with-fp-layout=endianflip as opposed to --with-fp-layout=nothing needs to be specified during configuration phase.

Signed-off-by Andrey Smirnov <[email protected]>

---
 package/collectd/collectd.mk | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

package/collectd/collectd.mk +0 -0

index 626fba81bf..80791b618d 100644

Hello,

Quoted 16 lines · Andrey Smirnov

PowerPC stores floating point as big endian, so, in order for 'network' plugin to work correctly (and potentially any user of htond() in collectd's codebase), --with-fp-layout=endianflip as opposed to --with-fp-layout=nothing needs to be specified during configuration phase.

Signed-off-by Andrey Smirnov <[email protected]>

---
 package/collectd/collectd.mk | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

package/collectd/collectd.mk +0 -0

index 626fba81bf..80791b618d 100644

package/collectd/collectd.mk COLLECTD_PLUGINS_DISABLE = \ · line 31

Quoted 8 lines

package/collectd/collectd.mk +5 -0

@@ -24,9 +24,15 @@ COLLECTD_PLUGINS_DISABLE = \
 
 COLLECTD_CONF_ENV += LIBS="-lm"
 
+ifeq ($(BR2_powerpc)$(BR2_powerpc64)$(BR2_powerpc64le),y)
+COLLECTD_FP_LAYOUT=endianflip
+else
+COLLECTD_FP_LAYOUT=nothing
+endif

I am not sure that the problem is PowerPC vs. rest of the world, but rather big endian vs. little endian. For example, OpenWRT is using endianflip on all big endian platforms, and "nothing" on all little endian platforms:
https://dev.openwrt.org/browser/packages/utils/collectd/Makefile?rev=28960.

So I believe the correct patch is to use:

ifeq ($(BR2_ENDIAN),"BIG")
COLLECTD_FP_LAYOUT = endianflip
else
COLLECTD_FP_LAYOUT = normal
endif

However, there is a third FP layout called "intswap", and I'm not sure in which situations it should be used. Some additional investigation of collectd configure.ac script is probably needed to understand the AC_RUN_IFELSE() tests it does to figure out what the FP layout is when doing a native build.

Quoted 6 lines

ifeq ($(BR2_ENDIAN),"BIG")
COLLECTD_FP_LAYOUT = endianflip
else
COLLECTD_FP_LAYOUT = normal
endif

Yeah, that sounds right. I implemented it PPC-only just because it was the only use-case I could test, but if OpenWRT is doing that for every big-endian arch, then it makes sens to change my patch to do the same.

I looked at that part of config.ac when I was debugging the problem and AFACT all "intswap()" does is swapping upper and lower 32-bits of a 64-bit word. I can't think of an architecture that would require such a transformation and commit that introduced that check in collectd didn't have any helpful hints either. Can we limit the scope of this fix to big vs. little endian the way you suggested and leave the "intswap" case out?

Quoted 6 lines

However, there is a third FP layout called "intswap", and I'm not sure in which situations it should be used. Some additional investigation of collectd configure.ac script is probably needed to understand the AC_RUN_IFELSE() tests it does to figure out what the FP layout is when doing a native build.

I looked at that part of config.ac when I was debugging the problem and AFACT all "intswap()" does is swapping upper and lower 32-bits of a 64-bit word. I can't think of an architecture that would require such a transformation and commit that introduced that check in collectd didn't have any helpful hints either. Can we limit the scope of this fix to big vs. little endian the way you suggested and leave the "intswap" case out?