[PATCH] reproducible builds: strip embedded file paths

[Vagrant Cascadian <vagrant@reproducible-builds.org>]

On 2021-11-22, Xiang W. wrote:
> ? 2021-11-18???? 17:05 -0800?Vagrant Cascadian???
>> 
>> Unfortunately, the use of __FILE__ can embed the absolute build path
>> in
>> the resulting binary, resulting in different binaries depending on
>> which
>> path the build was performed in.
>
> Under what scenarios will absolute paths be embed.

In each of the directories below, I built using the same toolchain from
the same git commit...

$ cd /home/vagrant/src/opensbi/opensbi1
$ CROSS_COMPILE=riscv64-linux-gnu- make V=1 FW_PAYLOAD=n PLATFORM=generic
...
$ strings build/platform/generic/firmware/fw_dynamic.bin | grep /home/vagrant
/home/vagrant/src/opensbi/opensbi1/lib/sbi/riscv_asm.c

$ cd /home/vagrant/src/opensbi/opensbi2
$ CROSS_COMPILE=riscv64-linux-gnu- make V=1 FW_PAYLOAD=n PLATFORM=generic
...
$ strings build/platform/generic/firmware/fw_dynamic.bin | grep /home/vagrant
/home/vagrant/src/opensbi/opensbi2/lib/sbi/riscv_asm.c


With the patch applied:

$ cd /home/vagrant/src/opensbi/opensbi3
$ CROSS_COMPILE=riscv64-linux-gnu- make V=1 FW_PAYLOAD=n PLATFORM=generic
...
$ strings build/platform/generic/firmware/fw_dynamic.bin  | grep /home/vagrant
$ strings build/platform/generic/firmware/fw_dynamic.bin  | grep riscv_asm.c
./lib/sbi/riscv_asm.c

A relative path within the source should be sufficient for the debug
message to properly identify the relevent source files...


An alternate approach would be to not use __FILE__ at all, but that
would probably take more code than passing -ffile-prefix-map at compile
time.


Thanks!


live well,
  vagrant