bug#42009: package.cache not deterministic

[zimoun <zimon.toutoune@gmail.com>]

Dear,

Thank you for the bug report.  It is something already noticed [1] but
without a clean bug report to track it. :-)

1: http://issues.guix.gnu.org/issue/39258#86


On Mon, 22 Jun 2020 at 19:07, Marinus <marinus.savoritias@disroot.org> wrote:

> Run into a determinism problem today with guix pull.
> I run guix pull --rounds=3 but guix ended in error that the result
> wasn't the same.

For reproducing, the simplest is:

--8<---------------cut here---------------start------------->8---
$ guix build --check --no-grafts -K \
   $(guix gc --derivers \
      $(readlink -f ~/.config/guix/current/lib/guix/package.cache))
The following profile hooks will be built:
   /gnu/store/l50sinckbl1y0fz2y4yk4vvfdvay9c8l-guix-package-cache.drv
   /gnu/store/h69hdf14c11q7dip0gssfd4cv0qw8j7k-guix-package-cache.drv
building package cache...
(repl-version 0 1 1)
Generating package cache for '/gnu/store/67zi87xwv2d90kx8pzxsbw2q7qkh11ns-profile'...
(values (value "/gnu/store/0009whxhfz00lm027wbars8q4wb3rvia-guix-package-cache/lib/guix/package.cache"))
guix build: error: derivation `/gnu/store/h69hdf14c11q7dip0gssfd4cv0qw8j7k-guix-package-cache.drv' may not be deterministic: output `/gnu/store/0009whxhfz00lm027wbars8q4wb3rvia-guix-package-cache' differs
--8<---------------cut here---------------end--------------->8---

Then the usual "diffoscope":

--8<---------------cut here---------------start------------->8---
diffoscope \
/gnu/store/0009whxhfz00lm027wbars8q4wb3rvia-guix-package-cache/lib/guix/package.cache \
/gnu/store/0009whxhfz00lm027wbars8q4wb3rvia-guix-package-cache-check/lib/guix/package.cache\
  | head -n50
--8<---------------cut here---------------end--------------->8---

outputs something like:

--8<---------------cut here---------------start------------->8---
--- /gnu/store/0009whxhfz00lm027wbars8q4wb3rvia-guix-package-cache/lib/guix/package.cache
+++ /gnu/store/0009whxhfz00lm027wbars8q4wb3rvia-guix-package-cache-check/lib/guix/package.cache
├── readelf --wide --file-header {}
│ @@ -6,15 +6,15 @@
│    OS/ABI:                            <unknown: ff>
│    ABI Version:                       0
│    Type:                              DYN (Shared object file)
│    Machine:                           None
│    Version:                           0x1
│    Entry point address:               0x0
│    Start of program headers:          64 (bytes into file)
│ -  Start of section headers:          4900296 (bytes into file)
│ +  Start of section headers:          4900456 (bytes into file)
│    Flags:                             0x0
│    Size of this header:               64 (bytes)
│    Size of program headers:           56 (bytes)
│    Number of program headers:         3
│    Size of section headers:           64 (bytes)
│    Number of section headers:         20
│    Section header string table index: 17
├── readelf --wide --program-header {}
│ @@ -1,16 +1,16 @@
│  
│  Elf file type is DYN (Shared object file)
│  Entry point 0x0
│  There are 3 program headers, starting at offset 64
│  
│  Program Headers:
│    Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
│ -  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x286a68 0x286a68 R   0x10000
│ -  LOAD           0x290000 0x0000000000290000 0x0000000000290000 0x21c5c8 0x21c5c8 RW  0x10000
│ -  DYNAMIC        0x286a08 0x0000000000286a08 0x0000000000286a08 0x000060 0x000060 R   0x8
│ +  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x286b78 0x286b78 R   0x10000
│ +  LOAD           0x290000 0x0000000000290000 0x0000000000290000 0x21c668 0x21c668 RW  0x10000
│ +  DYNAMIC        0x286b18 0x0000000000286b18 0x0000000000286b18 0x000060 0x000060 R   0x8
│  
│   Section to Segment mapping:
│    Segment Sections...
│     00     .rodata .rtl-text .dynamic  
│     01     .data 
│     02     .dynamic
├── readelf --wide --sections {}
│┄ stderr from `readelf --wide --sections {}`:
│┄ readelf: Warning: [ 5]: Link field (0) should index a string section.
│ @@ -1,29 +1,29 @@
│ -There are 20 section headers, starting at offset 0x4ac5c8:
│ +There are 20 section headers, starting at offset 0x4ac668:
--8<---------------cut here---------------end--------------->8---

Well, I do not know what should the next step.  I mean this
"package.cache" file is created by the function
gnu/packages.scm:(generate-package-cache) which reads:

--8<---------------cut here---------------start------------->8---
      ;; Store the cache as a '.go' file.  This makes loading fast and reduces
      ;; heap usage since some of the static data is directly mmapped.
      (put-bytevector port
                      (compile `'(,@exp)
                               #:to 'bytecode
                               #:opts '(#:to-file? #t)))))
--8<---------------cut here---------------end--------------->8---

Then it is on the Guile side, isn't it? 


All the best,
simon