[Mesa-dev] [PATCH 2/4] anv: use cache uuid based on the build timestamp.

[Michel Dänzer]

On 22.06.2016 21:04, Emil Velikov wrote:
> From: Emil Velikov <emil.velikov at collabora.com>
> 
> Do not rely on the git sha1:
>  - its current truncated form makes it less unique
>  - it does not attribute for local (Vulkand or otherwise) changes
> 
> Use a timestamp produced at the time of build. It's perfectly unique,
> unless someone explicitly thinkers with their system clock. Even then
> chances of producing the exact same one are very small, if not zero.
> 
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: mesa-stable at lists.freedesktop.org
> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> ---
> Current approach uses seconds since Epoch, but if people prefer we
> can use nano seconds, combination of the two and/or other.
> ---
>  src/intel/vulkan/.gitignore   |  2 ++
>  src/intel/vulkan/Makefile.am  | 15 ++++++++++++++-
>  src/intel/vulkan/anv_device.c |  4 ++--
>  3 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/src/intel/vulkan/.gitignore b/src/intel/vulkan/.gitignore
> index a496146..7ef6a48 100644
> --- a/src/intel/vulkan/.gitignore
> +++ b/src/intel/vulkan/.gitignore
> @@ -2,3 +2,5 @@
>  /anv_entrypoints.c
>  /anv_entrypoints.h
>  /dev_icd.json
> +/anv_timestamp.h.tmp
> +/anv_timestamp.h
> diff --git a/src/intel/vulkan/Makefile.am b/src/intel/vulkan/Makefile.am
> index 4d9ff90..8332ae5 100644
> --- a/src/intel/vulkan/Makefile.am
> +++ b/src/intel/vulkan/Makefile.am
> @@ -131,7 +131,20 @@ anv_entrypoints.c : anv_entrypoints_gen.py $(vulkan_include_HEADERS)
>  	$(AM_V_GEN) cat $(vulkan_include_HEADERS) |\
>  	$(PYTHON2) $(srcdir)/anv_entrypoints_gen.py code > $@
>  
> -BUILT_SOURCES = $(VULKAN_GENERATED_FILES)
> +
> +.PHONY: anv_timestamp.h.tmp
> +anv_timestamp.h.tmp:
> +	$(AM_V_GEN) echo "#define ANV_TIMESTAMP `date +%s`" > $@

This conflicts with efforts to make builds reproducible, see e.g.
https://wiki.debian.org/ReproducibleBuilds . One technique used by such
efforts is to replace any timestamps with all 0s.


Would it be possible to generate a hash over all source files listed in
any Makefile.sources, or something like that?


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer