Subject: Re: bug#41669: Cross-compiled powerpc64-linux bootstrap-tarballs not reproducible

From: Chris Marusich <[email-masked]>
Date: Tue, 09 Jun 2020 23:15:01 -0700

Hi Vincent and everyone,

Vincent Legoll <[email-masked]> writes:

> Is that showing the same (or a similar) problem :
>
> https://data.guix-patches.cbaines.net/gnu/store/0lcbxpw1vrca02dzpzw2rxhad7pn4zw7-gcc-objc-5.5.0
>
> ?

Can you clarify what you mean?  I'm not sure what you're referring to.

Chris Marusich <[email-masked]> writes:

> At present, it seems possible that within the context of a single
> machine, gcc-stripped-tarball-5.5.0.drv builds reproducibly, but on a
> different machine, it may (reproducibly) build a different output.
> I'm a bit paranoid about making mistakes, so I'll perform another full
> GC and then try yet again to build gcc-stripped-tarball-5.5.0.drv in
> order to verify whether it truly produces the same output when all (or
> nearly all) of its inputs are rebuilt from scratch.

I repeated the experiment on the same machine (it took a day or two to
build), and the result was the same: on my machine,
gcc-stripped-tarball-5.5.0.drv builds identical output to what it built
before. To be clear, using Guix 8159ce1970d91567468cf1bacac313099a009d2a
on an x86_64-linux machine, I tried (yet again) the following steps:

- I deleted as much as I could from the store using 'guix gc'.

- I explicitly verified that all outputs for the following derivations
  no longer existed in the store:

  /gnu/store/pygln3lr6qbxcps3kmn3w4bc0d0nlpd3-gcc-stripped-tarball-5.5.0.drv
  /gnu/store/kcv3ja1rfr93hw6ly51878zjhdwpgv7z-gcc-stripped-5.5.0.drv
  /gnu/store/m9hfwppla8lph0vxa15lfkp81s2bbjjs-gcc-static-5.5.0.drv
  /gnu/store/g9fpkg2qa27mka1znqsvx8vxqyabsj2y-gcc-7.5.0.drv

- I then built gcc-stripped-tarball-5.5.0.drv via the following command:

  guix build --no-substitutes --check --target=powerpc64-linux-gnu \
       -e '(@@ (gnu packages make-bootstrap) %gcc-static)'

This rebuilt basically everything, including gcc-7.5.0.drv and the other
derivations mentioned above.  When I checked the built output of the
gcc-stripped-tarball-5.5.0.drv derivation, I found that its SHA-512 hash
was identical to the one I calculated previously, which was:

--8<---------------cut here---------------start------------->8---
8aca7f332a1ba8e3c2225c161a7545b0a04ddd690d164dc97afee9c9ea067b0c49bc155e9f06d285c22e24cdd16d91e59730af5f1dd9efcda13a26bede5948a2  /gnu/store/rsmhiyplmbiqm1qwniiafi4ak76pd61v-gcc-stripped-tarball-5.5.0/gcc-stripped-5.5.0-powerpc64-linux-gnu.tar.xz
--8<---------------cut here---------------end--------------->8---

Anyway, this confirms what we already knew: GCC builds reproducibly on
my machine, but it is different when other people build it on other
machines.  I'm now quite convinced of this fact.

Jack and Vincent shared their build results on the email list.  For
reference, you can get them here:

https://flashner.co.il/~efraim/gcc-stripped-5.5.0-powerpc64-linux-gnu.tar.xz
https://jackhill.us/misc/gcc-stripped-5.5.0-powerpc64-linux-gnu.tar.xz
https://media.marusich.info/gcc-stripped-5.5.0-powerpc64-linux-gnu.tar.xz

I also received a copy of Vincent's build results via private email.  In
short, they all seem to differ in basically the same ways:

--8<---------------cut here---------------start------------->8---
[1] marusich@garuda-lan:~/Documents/notes/guix/ppc/gcc-stripped-tarballs
$ diff -r chris jack
Binary files chris/bin/c++ and jack/bin/c++ differ
Binary files chris/bin/cpp and jack/bin/cpp differ
Binary files chris/bin/g++ and jack/bin/g++ differ
Binary files chris/bin/gcc and jack/bin/gcc differ
Binary files chris/bin/gcov and jack/bin/gcov differ
Binary files chris/bin/gcov-dump and jack/bin/gcov-dump differ
Binary files chris/bin/gcov-tool and jack/bin/gcov-tool differ
Binary files chris/bin/powerpc64-linux-gnu-c++ and jack/bin/powerpc64-linux-gnu-c++ differ
Binary files chris/bin/powerpc64-linux-gnu-g++ and jack/bin/powerpc64-linux-gnu-g++ differ
Binary files chris/bin/powerpc64-linux-gnu-gcc and jack/bin/powerpc64-linux-gnu-gcc differ
Binary files chris/bin/powerpc64-linux-gnu-gcc-5.5.0 and jack/bin/powerpc64-linux-gnu-gcc-5.5.0 differ
Binary files chris/lib/libstdc++.a and jack/lib/libstdc++.a differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1 and jack/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1 differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1plus and jack/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1plus differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/collect2 and jack/libexec/gcc/powerpc64-linux-gnu/5.5.0/collect2 differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/lto-wrapper and jack/libexec/gcc/powerpc64-linux-gnu/5.5.0/lto-wrapper differ
[1] marusich@garuda-lan:~/Documents/notes/guix/ppc/gcc-stripped-tarballs
$ diff -r chris vincent
Binary files chris/bin/c++ and vincent/bin/c++ differ
Binary files chris/bin/cpp and vincent/bin/cpp differ
Binary files chris/bin/g++ and vincent/bin/g++ differ
Binary files chris/bin/gcc and vincent/bin/gcc differ
Binary files chris/bin/gcov and vincent/bin/gcov differ
Binary files chris/bin/gcov-dump and vincent/bin/gcov-dump differ
Binary files chris/bin/gcov-tool and vincent/bin/gcov-tool differ
Binary files chris/bin/powerpc64-linux-gnu-c++ and vincent/bin/powerpc64-linux-gnu-c++ differ
Binary files chris/bin/powerpc64-linux-gnu-g++ and vincent/bin/powerpc64-linux-gnu-g++ differ
Binary files chris/bin/powerpc64-linux-gnu-gcc and vincent/bin/powerpc64-linux-gnu-gcc differ
Binary files chris/bin/powerpc64-linux-gnu-gcc-5.5.0 and vincent/bin/powerpc64-linux-gnu-gcc-5.5.0 differ
Binary files chris/lib/libstdc++.a and vincent/lib/libstdc++.a differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1 and vincent/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1 differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1plus and vincent/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1plus differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/collect2 and vincent/libexec/gcc/powerpc64-linux-gnu/5.5.0/collect2 differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/lto-wrapper and vincent/libexec/gcc/powerpc64-linux-gnu/5.5.0/lto-wrapper differ
[1] marusich@garuda-lan:~/Documents/notes/guix/ppc/gcc-stripped-tarballs
$ diff -r chris efraim
Binary files chris/bin/c++ and efraim/bin/c++ differ
Binary files chris/bin/cpp and efraim/bin/cpp differ
Binary files chris/bin/g++ and efraim/bin/g++ differ
Binary files chris/bin/gcc and efraim/bin/gcc differ
Binary files chris/bin/gcov and efraim/bin/gcov differ
Binary files chris/bin/gcov-dump and efraim/bin/gcov-dump differ
Binary files chris/bin/gcov-tool and efraim/bin/gcov-tool differ
Binary files chris/bin/powerpc64-linux-gnu-c++ and efraim/bin/powerpc64-linux-gnu-c++ differ
Binary files chris/bin/powerpc64-linux-gnu-g++ and efraim/bin/powerpc64-linux-gnu-g++ differ
Binary files chris/bin/powerpc64-linux-gnu-gcc and efraim/bin/powerpc64-linux-gnu-gcc differ
Binary files chris/bin/powerpc64-linux-gnu-gcc-5.5.0 and efraim/bin/powerpc64-linux-gnu-gcc-5.5.0 differ
diff -r chris/lib/gcc/powerpc64-linux-gnu/5.5.0/include-fixed/bits/statx.h efraim/lib/gcc/powerpc64-linux-gnu/5.5.0/include-fixed/bits/statx.h
5c5
< 	"/gnu/store/fa6wj5bxkj5ll1d7292a70knmyl7a0cr-glibc-2.31/include/bits/statx.h"
---
> 	"/gnu/store/cb88z63hyg1icd2kkahiink2p291mhr2-glibc-2.31/include/bits/statx.h"
Binary files chris/lib/libstdc++.a and efraim/lib/libstdc++.a differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1 and efraim/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1 differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1plus and efraim/libexec/gcc/powerpc64-linux-gnu/5.5.0/cc1plus differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/collect2 and efraim/libexec/gcc/powerpc64-linux-gnu/5.5.0/collect2 differ
Binary files chris/libexec/gcc/powerpc64-linux-gnu/5.5.0/lto-wrapper and efraim/libexec/gcc/powerpc64-linux-gnu/5.5.0/lto-wrapper differ
[1] marusich@garuda-lan:~/Documents/notes/guix/ppc/gcc-stripped-tarballs
$ 
--8<---------------cut here---------------end--------------->8---

Efraim's diff looks a little different in statx.h, even though he used
the same Guix commit as me.  Maybe this is because he cross-compiled on
an aarch64-linux machine, while I cross-compiled on an x86_64-linux
machine.  In the other cases, it looks like the binary files differ in
basically the same ways.  I will share some examples below.

Here is some diffoscope output between my c++ and Efraim's (many other
sections also differed in similarly cryptic ways):

--8<---------------cut here---------------start------------->8---
diffoscope chris/bin/c++ efraim/bin/c++
...
├── /gnu/store/xakj5dgs1729297nv50s84sdmq2jiz64-binutils-2.34/bin/readelf --wide --symbols {}
│ @@ -328,18 +328,18 @@
│     324: 00000000101aece0   152 FUNC    LOCAL  DEFAULT   19 check_free.isra.0
│     325: 00000000101aed28    24 FUNC    LOCAL  DEFAULT   19 fini
│     326: 00000000101b6008     8 OBJECT  LOCAL  DEFAULT   24 static_buf
│     327: 00000000101b6010    32 OBJECT  LOCAL  DEFAULT   24 last_result
│     328: 00000000101b6030     4 OBJECT  LOCAL  DEFAULT   24 key
│     329: 00000000101b6034     4 OBJECT  LOCAL  DEFAULT   24 once
│     330: 00000000101b23b8   104 OBJECT  LOCAL  DEFAULT   22 _dlfcn_hooks
│ -   331: 00000000101a98f8   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool4freeEPv.constprop.2
│ -   332: 00000000101a9910   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool8allocateEm.constprop.3
│ -   333: 00000000101a99a0   180 FUNC    LOCAL  DEFAULT   19 _GLOBAL__sub_I_eh_alloc.cc
│ -   334: 00000000101b4f68    64 OBJECT  LOCAL  DEFAULT   24 _ZN12_GLOBAL__N_114emergency_poolE
│ +   331: 00000000101a9880   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool4freeEPv.constprop.2
│ +   332: 00000000101a9898   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool8allocateEm.constprop.3
│ +   333: 00000000101a9928   180 FUNC    LOCAL  DEFAULT   19 _GLOBAL__sub_I_eh_alloc.cc
│ +   334: 00000000101b4f78    64 OBJECT  LOCAL  DEFAULT   24 _ZN12_GLOBAL__N_114emergency_poolE
│     335: 000000001011c5a8    19 OBJECT  LOCAL  DEFAULT    7 _ZZ18ggc_internal_allocmPFvPvEmmE12__FUNCTION__
│     336: 000000001011c5c0    27 OBJECT  LOCAL  DEFAULT    7 _ZZ26ggc_internal_cleared_allocmPFvPvEmmE12__FUNCTION__
│     337: 000000001011c600    21 OBJECT  LOCAL  DEFAULT    7 _ZZ20lang_specific_driverPP17cl_decoded_optionPjPiE12__FUNCTION__
│     338: 00000000101a42d0   228 FUNC    LOCAL  DEFAULT   19 _ZL12elf_platformv
│     339: 00000000101a42e8   236 FUNC    LOCAL  DEFAULT   19 _ZL15elf_dcachebsizev
│     340: 00000000101a4300   164 FUNC    LOCAL  DEFAULT   19 _ZL14describe_cachejjjj.isra.0.constprop.1
│     341: 000000001011c6b8   752 OBJECT  LOCAL  DEFAULT    7 _ZL9asm_names
...
│ @@ -1379,25 +1379,25 @@
│    1375: 00000000101b2448     0 SECTION LOCAL  DEFAULT   23 
│    1376: 00000000101b2b80     0 SECTION LOCAL  DEFAULT   24 
│    1377: 00000000101b6860     0 SECTION LOCAL  DEFAULT   25 
│    1378: 0000000000000000     0 SECTION LOCAL  DEFAULT   26 
│    1379: 0000000000000000     0 SECTION LOCAL  DEFAULT   27 
│    1380: 00000000101a2a28   752 OBJECT  GLOBAL DEFAULT   18 _nl_C_LC_CTYPE
│    1381: 00000000101ace20    56 IFUNC   GLOBAL DEFAULT   19 __libc_strcspn
│ -  1382: 00000000101a9958   100 FUNC    GLOBAL DEFAULT   19 __cxa_free_exception
│ +  1382: 00000000101a98e0   100 FUNC    GLOBAL DEFAULT   19 __cxa_free_exception
│    1383: 00000000101acfe8   104 FUNC    WEAK   DEFAULT   19 stpcpy
│    1384: 00000000101ab7e8   516 FUNC    GLOBAL DEFAULT   19 putchar
│ -  1385: 00000000101a9598    20 FUNC    GLOBAL DEFAULT   19 _ZNKSt9type_info15__is_function_pEv
│ +  1385: 00000000101a9778    20 FUNC    GLOBAL DEFAULT   19 _ZNKSt9type_info15__is_function_pEv
│    1386: 000000001016a3cc    76 OBJECT  GLOBAL DEFAULT    7 _nl_C_LC_CTYPE_class_print
│    1387: 00000000101adfc0   640 FUNC    WEAK   DEFAULT   19 tsearch
│    1388: 00000000101af0a0   176 FUNC    WEAK   DEFAULT   19 clock_gettime
│    1389: 00000000101a4150  4856 FUNC    GLOBAL DEFAULT   19 _ZNK6driver12set_up_specsEv
│    1390: 00000000101a9268    88 FUNC    GLOBAL DEFAULT   19 xmalloc
│    1391: 00000000101b1d68     8 OBJECT  GLOBAL DEFAULT   22 __morecore
│ -  1392: 00000000101a9568    40 FUNC    GLOBAL DEFAULT   19 _ZSt10unexpectedv
│ +  1392: 00000000101a94f0    40 FUNC    GLOBAL DEFAULT   19 _ZSt10unexpectedv
│    1393: 00000000101a8ef0    60 FUNC    GLOBAL DEFAULT   19 lbasename
│    1394: 00000000101aded0    96 FUNC    GLOBAL DEFAULT   19 __getdtablesize
│    1395: 00000000101a4348   752 FUNC    GLOBAL DEFAULT   19 update_path
...
├── /gnu/store/xakj5dgs1729297nv50s84sdmq2jiz64-binutils-2.34/bin/readelf --wide --decompress --hex-dump=.data.rel.ro {}
│ @@ -112,27 +112,27 @@
│    0x101a1718 00000000 10164560 00000009 00000001 ......E`........
│    0x101a1728 00000000 10164570 00000000 10164578 ......Ep......Ex
│    0x101a1738 0000000c 00000002 00000000 101499e8 ................
│    0x101a1748 00000000 10116018 00000001 00000001 ......`.........
│    0x101a1758 00000000 10164588 00000000 10164590 ......E.......E.
│    0x101a1768 00000007 00000001 00000000 10119850 ...............P
│    0x101a1778 00000000 1015e290 00000002 00000002 ................
│ -  0x101a1788 00000000 101641c0 00000000 101653e8 ......A.......S.
│ +  0x101a1788 00000000 101641c0 00000000 101653a8 ......A.......S.
│    0x101a1798 00000001 00000002 00000000 10164598 ..............E.
│    0x101a17a8 00000000 10117df0 00000001 00000002 ......}.........
│    0x101a17b8 00000000 101645a0 00000000 1015e238 ......E........8
│    0x101a17c8 00000002 00000002 00000000 101645a8 ..............E.
│    0x101a17d8 00000000 101631d8 00000001 00000002 ......1.........
│    0x101a17e8 00000000 101645b0 00000000 1015e1e0 ......E.........
│ -  0x101a17f8 00000002 00000002 00000000 101653c0 ..............S.
│ +  0x101a17f8 00000002 00000002 00000000 10165380 ..............S.
│    0x101a1808 00000000 1015e268 00000003 00000003 .......h........
│ -  0x101a1818 00000000 101653c8 00000000 1015e268 ......S........h
│ -  0x101a1828 00000003 00000003 00000000 101653d0 ..............S.
│ +  0x101a1818 00000000 10165388 00000000 1015e268 ......S........h
│ +  0x101a1828 00000003 00000003 00000000 10165390 ..............S.
│    0x101a1838 00000000 1015e268 00000003 00000002 .......h........
│ -  0x101a1848 00000000 101653d8 00000000 1015e268 ......S........h
│ +  0x101a1848 00000000 10165398 00000000 1015e268 ......S........h
│    0x101a1858 00000003 00000002 00000000 10144ea8 ..............N.
│    0x101a1868 00000000 1015e1f0 00000002 00000002 ................
...
--8<---------------cut here---------------end--------------->8---

Here is some diffoscope output betweeen my c++ and Jack's (many other
sections also differed in similarly cryptic ways):

--8<---------------cut here---------------start------------->8---
diffoscope chris/bin/c++ jack/bin/c++
...
├── /gnu/store/xakj5dgs1729297nv50s84sdmq2jiz64-binutils-2.34/bin/readelf --wide --symbols {}
│ @@ -328,17 +328,17 @@
│     324: 00000000101aece0   152 FUNC    LOCAL  DEFAULT   19 check_free.isra.0
│     325: 00000000101aed28    24 FUNC    LOCAL  DEFAULT   19 fini
│     326: 00000000101b6008     8 OBJECT  LOCAL  DEFAULT   24 static_buf
│     327: 00000000101b6010    32 OBJECT  LOCAL  DEFAULT   24 last_result
│     328: 00000000101b6030     4 OBJECT  LOCAL  DEFAULT   24 key
│     329: 00000000101b6034     4 OBJECT  LOCAL  DEFAULT   24 once
│     330: 00000000101b23b8   104 OBJECT  LOCAL  DEFAULT   22 _dlfcn_hooks
│ -   331: 00000000101a98f8   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool4freeEPv.constprop.2
│ -   332: 00000000101a9910   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool8allocateEm.constprop.3
│ -   333: 00000000101a99a0   180 FUNC    LOCAL  DEFAULT   19 _GLOBAL__sub_I_eh_alloc.cc
│ +   331: 00000000101a94c0   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool4freeEPv.constprop.2
│ +   332: 00000000101a94d8   524 FUNC    LOCAL  DEFAULT   19 _ZN12_GLOBAL__N_14pool8allocateEm.constprop.3
│ +   333: 00000000101a9568   180 FUNC    LOCAL  DEFAULT   19 _GLOBAL__sub_I_eh_alloc.cc
│     334: 00000000101b4f68    64 OBJECT  LOCAL  DEFAULT   24 _ZN12_GLOBAL__N_114emergency_poolE
│     335: 000000001011c5a8    19 OBJECT  LOCAL  DEFAULT    7 _ZZ18ggc_internal_allocmPFvPvEmmE12__FUNCTION__
│     336: 000000001011c5c0    27 OBJECT  LOCAL  DEFAULT    7 _ZZ26ggc_internal_cleared_allocmPFvPvEmmE12__FUNCTION__
│     337: 000000001011c600    21 OBJECT  LOCAL  DEFAULT    7 _ZZ20lang_specific_driverPP17cl_decoded_optionPjPiE12__FUNCTION__
│     338: 00000000101a42d0   228 FUNC    LOCAL  DEFAULT   19 _ZL12elf_platformv
│     339: 00000000101a42e8   236 FUNC    LOCAL  DEFAULT   19 _ZL15elf_dcachebsizev
│     340: 00000000101a4300   164 FUNC    LOCAL  DEFAULT   19 _ZL14describe_cachejjjj.isra.0.constprop.1
...
├── /gnu/store/xakj5dgs1729297nv50s84sdmq2jiz64-binutils-2.34/bin/readelf --wide --decompress --hex-dump=.data.rel.ro {}
│ @@ -206,60 +206,60 @@
│    0x101a1cf8 00000000 101a3b08 00000000 10118108 ......;.........
│    0x101a1d08 00000000 101a4120 00000000 10118120 ......A ....... 
│    0x101a1d18 00000000 101a4108 00000000 10115758 ......A.......WX
│    0x101a1d28 00000000 101a3a60 00000000 10118138 ......:`.......8
│    0x101a1d38 00000000 101a3a48 00000000 10115ae8 ......:H......Z.
│    0x101a1d48 00000000 101a3c10 00000000 10118150 ......<........P
│    0x101a1d58 00000000 101a4318 00000000 00000000 ......C.........
│ -  0x101a1d68 00000000 00000000 00000000 101a1dd8 ................
│ -  0x101a1d78 00000000 101650d0 00000000 101a1e70 ......P........p
│ -  0x101a1d88 00000000 00000000 00000000 101a1d70 ...............p
│ -  0x101a1d98 00000000 101a9388 00000000 101a93a0 ................
│ -  0x101a1da8 00000000 101a9370 00000000 101a1dd8 .......p........
│ -  0x101a1db8 00000000 101650f0 00000000 101a1fd8 ......P.........
│ -  0x101a1dc8 00000000 00000000 00000000 101a1db0 ................
│ -  0x101a1dd8 00000000 101a93d0 00000000 101a93e8 ................
│ -  0x101a1de8 00000000 101a9598 00000000 101a9598 ................
│ -  0x101a1df8 00000000 101a9b20 00000000 101a9a90 ....... ........
│ -  0x101a1e08 00000000 101a9430 00000000 101a9418 .......0........
│ -  0x101a1e18 00000000 101a9400 00000000 101a2000 .............. .
│ -  0x101a1e28 00000000 10165118 00000000 00000000 ......Q.........
│ -  0x101a1e38 00000000 101a1e20 00000000 101a9580 ....... ........
│ -  0x101a1e48 00000000 101a95c8 00000000 101a9598 ................
│ -  0x101a1e58 00000000 101a9598 00000000 101a95e0 ................
│ -  0x101a1e68 00000000 101a95b0 00000000 101a2000 .............. .
│ -  0x101a1e78 00000000 10165128 00000000 101a1dd8 ......Q(........
│ -  0x101a1e88 00000000 10165138 00000000 101a1e70 ......Q8.......p
│ -  0x101a1e98 00000000 101a2000 00000000 10165150 ...... .......QP
│ -  0x101a1ea8 00000000 101a2000 00000000 10165170 ...... .......Qp
│ -  0x101a1eb8 00000000 00000000 00000000 101a1e70 ...............p
│ -  0x101a1ec8 00000000 101a96e8 00000000 101a9748 ...............H
│ -  0x101a1ed8 00000000 101a9718 00000000 00000000 ................
│ -  0x101a1ee8 00000000 101a1e80 00000000 101a9700 ................
│ -  0x101a1ef8 00000000 101a9760 00000000 101a9730 .......`.......0
│ -  0x101a1f08 00000000 00000000 00000000 101a1e98 ................
│ -  0x101a1f18 00000000 00000000 00000000 00000000 ................
│ -  0x101a1f28 00000000 101a99b8 00000000 00000000 ................
│ -  0x101a1f38 00000000 101a1ea8 00000000 00000000 ................
│ -  0x101a1f48 00000000 00000000 00000000 101a99b8 ................
│ -  0x101a1f58 00000000 101a1dd8 00000000 101651c0 ..............Q.
│ -  0x101a1f68 00000000 101a1e70 00000000 101a1dd8 .......p........
│ -  0x101a1f78 00000000 101651e8 00000000 101a1e70 ......Q........p
│ -  0x101a1f88 00000000 00000000 00000000 101a1f58 ...............X
│ -  0x101a1f98 00000000 101a9880 00000000 101a98b0 ................
│ -  0x101a1fa8 00000000 101a9850 00000000 00000000 .......P........
│ -  0x101a1fb8 00000000 101a1f70 00000000 101a9898 .......p........
│ -  0x101a1fc8 00000000 101a98c8 00000000 101a9868 ...............h
│ -  0x101a1fd8 00000000 101a1dd8 00000000 101652a8 ..............R.
│ -  0x101a1fe8 00000000 101a1e20 00000000 00000000 ....... ........
│ -  0x101a1ff8 00000000 101a1fd8 00000000 101a9ac0 ................
│ -  0x101a2008 00000000 101a9ad8 00000000 101a9598 ................
│ -  0x101a2018 00000000 101a9598 00000000 101a9b20 ............... 
│ -  0x101a2028 00000000 101a9a90 00000000 101a9b08 ................
│ -  0x101a2038 00000000 101a9af0 00000000 101a9aa8 ................
│ +  0x101a1d68 00000000 00000000 00000000 101a1f40 ...............@
│ +  0x101a1d78 00000000 101650d0 00000000 101a1e30 ......P........0
│ +  0x101a1d88 00000000 101a1f40 00000000 101650f8 .......@......P.
│ +  0x101a1d98 00000000 101a1e30 00000000 00000000 .......0........
│ +  0x101a1da8 00000000 101a1d70 00000000 101a9448 .......p.......H
│ +  0x101a1db8 00000000 101a9478 00000000 101a9418 .......x........
│ +  0x101a1dc8 00000000 00000000 00000000 101a1d88 ................
│ +  0x101a1dd8 00000000 101a9460 00000000 101a9490 .......`........
│ +  0x101a1de8 00000000 101a9430 00000000 101a1f40 .......0.......@
│ +  0x101a1df8 00000000 10165178 00000000 101a1e30 ......Qx.......0
│ +  0x101a1e08 00000000 00000000 00000000 101a1df0 ................
│ +  0x101a1e18 00000000 101a9610 00000000 101a9628 ...............(
│ +  0x101a1e28 00000000 101a95f8 00000000 101a1fb0 ................
│ +  0x101a1e38 00000000 10165198 00000000 101a1f40 ......Q........@
│ +  0x101a1e48 00000000 101651a8 00000000 101a1e30 ......Q........0
│ +  0x101a1e58 00000000 101a1fb0 00000000 101651c0 ..............Q.
│ +  0x101a1e68 00000000 101a1fb0 00000000 101651e0 ..............Q.
│ +  0x101a1e78 00000000 00000000 00000000 101a1e30 ...............0
│ +  0x101a1e88 00000000 101a9760 00000000 101a97c0 .......`........
│ +  0x101a1e98 00000000 101a9790 00000000 00000000 ................
│ +  0x101a1ea8 00000000 101a1e40 00000000 101a9778 .......@.......x
│ +  0x101a1eb8 00000000 101a97d8 00000000 101a97a8 ................
│ +  0x101a1ec8 00000000 00000000 00000000 101a1e58 ...............X
│ +  0x101a1ed8 00000000 00000000 00000000 00000000 ................
│ +  0x101a1ee8 00000000 101a98b0 00000000 00000000 ................
│ +  0x101a1ef8 00000000 101a1e68 00000000 00000000 .......h........
│ +  0x101a1f08 00000000 00000000 00000000 101a98b0 ................
│ +  0x101a1f18 00000000 101a1f40 00000000 10165270 .......@......Rp
│ +  0x101a1f28 00000000 101a1f88 00000000 00000000 ................
│ +  0x101a1f38 00000000 101a1f18 00000000 101a98e0 ................
│ +  0x101a1f48 00000000 101a98f8 00000000 101a9af0 ................
│ +  0x101a1f58 00000000 101a9af0 00000000 101a9ac0 ................
│ +  0x101a1f68 00000000 101a9a30 00000000 101a9940 .......0.......@
│ +  0x101a1f78 00000000 101a9928 00000000 101a9910 .......(........
│ +  0x101a1f88 00000000 101a1f40 00000000 10165298 .......@......R.
│ +  0x101a1f98 00000000 101a1ff8 00000000 00000000 ................
│ +  0x101a1fa8 00000000 101a1f88 00000000 101a9a60 ...............`
│ +  0x101a1fb8 00000000 101a9a78 00000000 101a9af0 .......x........
│ +  0x101a1fc8 00000000 101a9af0 00000000 101a9ac0 ................
│ +  0x101a1fd8 00000000 101a9a30 00000000 101a9aa8 .......0........
│ +  0x101a1fe8 00000000 101a9a90 00000000 101a9a48 ...............H
│ +  0x101a1ff8 00000000 101a1fb0 00000000 101652c0 ..............R.
│ +  0x101a2008 00000000 00000000 00000000 101a1ff8 ................
│ +  0x101a2018 00000000 101a9ad8 00000000 101a9b20 ............... 
│ +  0x101a2028 00000000 101a9af0 00000000 101a9af0 ................
│ +  0x101a2038 00000000 101a9b38 00000000 101a9b08 .......8........
│    0x101a2048 00000000 10165a28 00000000 101aa888 ......Z(........
│    0x101a2058 00000000 00000000 04040404 00000000 ................
│    0x101a2068 00000000 10165a38 00000000 101aa8a0 ......Z8........
│    0x101a2078 00000000 00000000 04040404 00000000 ................
│    0x101a2088 00000000 10165a58 00000000 101aa8b8 ......ZX........
│    0x101a2098 00000000 00000000 04040404 00000000 ................
│    0x101a20a8 00000000 10165a70 00000000 101aa8d0 ......Zp........
--8<---------------cut here---------------end--------------->8---

If I'm reading this correctly, one problem seems to be that our GCC
toolchains are putting symbols at different locations.  This issue (and
maybe others) could be trickling down, causing other aspects of the
binaries to differ (e.g., in length).  Nothing really stands out, but
when we discussed this on IRC, we thought perhaps factors like the
following might contribute to the non-reproducibility:

- Perhaps we are all running different Linux kernel versions?  In some
  cases, the kernel version can unfortunately influence the build
  output, so this might be worth testing.

- Perhaps the GCC Makefiles etc. are doing something non-deterministic?

- Something else?

Avenues of investigation:

- If anything obvious stands out from the diffoscope output, please
  leave a comment.

- Try building with different kernel versions on the same machine, to
  see if they differ.

- If somebody else could please confirm that running the following
  command reports no difference on their own machine (i.e., exit code
  0), that would be good to know, since it would help further solidify
  the theory that on a single machine, the build of gcc-static-5.5.0.drv
  is reproducible, even if it is not reproducible across machines:

  guix build --no-substitutes --check --target=powerpc64-linux-gnu \
       -e '(@@ (gnu packages make-bootstrap) %gcc-static)'

- Try building two different versions of gcc-7.5.0 (maybe by hand?), and
  then use them to build a simple reproduction case and compare results.
  If we're lucky, maybe this will help us understand the problem better.

We'll get there!

-- 
Chris