[ccache] feature wishes and questions

[Basile STARYNKEVITCH]

Dear Ccache developers

I'm giving here some features I would wish to suggest for
ccache. Unfortunately, I don't have the incentive or time to develop
them.

First (and this is actually a question) how to deal with cache
corruption. My laptop (MSI S270 - see
http://starynkevitch.net/Basile/msi_s270_linux.html for more - seems
to have occasionaly problems (maybe memory, but memtest don't detact
any errors in a 12hour run, maybe bus controller?)

The symptom is for example that a cc1 or as pass of the gcc compiler
output a single wrong bit, or (for as) got a single wrong bit on
input. For a concrete example (this one is a kernel compile not using
ccache, but it is the only example I actually saved to a file)

  CC      drivers/message/i2o/i2o_config.mod.o
  LD [M]  drivers/message/i2o/i2o_config.ko
  CC      drivers/message/i2o/i2o_core.mod.o
  LD [M]  drivers/message/i2o/i2o_core.ko
  CC      drivers/message/i2o/i2o_proc.mod.o
{standard input}: Assembler messages:
{standard input}:6185: Error: unknown pseudo-op: `.uleb1'
{standard input}:6186: Error: junk at end of line, first unrecognized character is `"'
make[1]: *** [drivers/message/i2o/i2o_proc.mod.o] Error 1
make: *** [modules] Error 2

Then I restart thru make, and the same file is compiled ok:


  Building modules, stage 2.
  MODPOST
  CC      drivers/message/i2o/i2o_proc.mod.o
  LD [M]  drivers/message/i2o/i2o_proc.ko

So you see that the produced assembly got a .uleb1 instead of .ulab1
directive. This is a single-bit error.

I once (when compîling Qt4 snapshot) got a similar error, and the
erronous .o file got into ccache ~/.ccache file. I saw no other way to
remove this fault from the cache that to erase the entire cache. It
took me a whole hour (ok I am a ccache newbie) to guess that the fault
was indeed stored in the cache ~/.ccache of ccache.

This brings several suggestions

1. have an option to force recompilation (ie behave as if there is
   always a cache miss), like

   ccache -F gcc ....


2. have some log option which tell in which file a given compilation
   is cached (the source code of ccache seems to suggest there is
   something for this, I didn't found it yet).


I also have another question: if the same file foo.c is in 2 different
directories compiled the same way, does the compilation from the first
directory serves as cache for the second one? And what if dir1/foo.c
is the same as dir2/foo2.c?

Also, can we remove individual files from the cache?

Regards, and thanks for your good work!
 
-- 
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/ 
email: basile(at)starynkevitch(dot)net 
8, rue de la Faïencerie, 92340 Bourg La Reine, France