[OE-core] glibc binary reproducibility

[Richard Purdie]

On Thu, 2018-09-27 at 12:18 +1200, Douglas Royds wrote:
> > $ arm-tait-linux-gnueabi-gcc  -march=armv5te -marm -mcpu=arm926ej-s 
> > --sysroot=/home/douglas/workspace/upstream1/build/tmp/work/armv5e-
> > tait-linux-gnueabi/glibc/2.28-r0/recipe-sysroot -nostdlib
> > -nostartfiles -r -o
> > /home/douglas/workspace/upstream1/build/tmp/work/armv5e-tait-linux-
> > gnueabi/glibc/2.28-r0/build-arm-tait-linux-gnueabi/csu/crt1.o
> > /home/douglas/workspace/upstream1/build/tmp/work/armv5e-tait-linux-
> > gnueabi/glibc/2.28-r0/build-arm-tait-linux-gnueabi/csu/start.o
> > /home/douglas/workspace/upstream1/build/tmp/work/armv5e-tait-linux-
> > gnueabi/glibc/2.28-r0/build-arm-tait-linux-gnueabi/csu/abi-note.o
> > /home/douglas/workspace/upstream1/build/tmp/work/armv5e-tait-linux-
> > gnueabi/glibc/2.28-r0/build-arm-tait-linux-gnueabi/csu/init.o
> > /home/douglas/workspace/upstream1/build/tmp/work/armv5e-tait-linux-
> > gnueabi/glibc/2.28-r0/build-arm-tait-linux-gnueabi/csu/static-
> > reloc.o
> 
> Note the -r = --relocatable, an ld option, which, "Generate[s]
> relocatable output---i.e., generate[s] an output file that can in
> turn serve as input to ld.  This is often called partial linking",
> ie. the glibc build is just putting these .o files together for later
> convenience.
> Regrettably, this command both ignores -fdebug-prefix-map (which ld
> doesn't accept) and puts the fully-qualified path to some of the
> input .o files in the resulting crt1.o. At package splitdebuginfo()
> time, although the fully-qualified path info is split off into the
> .debug files, a (relative) path to the .debug files plus a checksum
> is tacked onto libc.so by objcopy --add-gnu-debuglink ... and the
> checksum depends on the path to the build.
> There is a work-around: turn off the debug packaging:
> > INHIBIT_PACKAGE_DEBUG_SPLIT_pn-glibc = "1"
> 
> I don't have a solution for this. Suggestions?

Good work in tracking it down so far.

Going off a bit of a random memory fragment, would it help to use
relative paths in the compile/link command?

Cheers,

Richard