[Buildroot] [PATCH] package/libcap: don't overwrite 'empty' when generating loader.txt

[Arnout Vandecappelle]

On 24/08/2021 09:13, Yann E. MORIN wrote:
> Arnout, All,
> 
> On 2021-08-24 01:31 +0200, Arnout Vandecappelle (Essensium/Mind) spake thusly:
>> Upstream commit [1] introduced an invocation of objcopy to generat
>> loader.txt. However, objcopy, if not provided with an output file, will
>> overwrite the input file. This is usually harmless because it will be
>> identical, but the timestamp is updated. This may cause 'empty' to be
>> newer than 'loader.txt', which causes 'loader.txt' and its dependencies
>> to be rebuilt during 'make install'
>>
>> We provide a different set of parameters during 'make install'. In
>> particular, we no longer pass in HOST_CONFIGURE_OPTS, so we no longer
>> set LDFLAGS. Thus, there is no -Wl,rpath option that is passed in, which
>> causes the resulting binaries to have an incorrect RPATH.
>>
>> Fix this by adding /dev/null as the output file in the objcopy
>> invocation.
>>
>> Patch was sent upstream, but there's no mailing list, just a single
>> person.
>>
>> Fixes: http://autobuild.buildroot.net/results/600/600aff5b839b48db80751cace5fa9670b7a3d698
>> (hopefully)
>>
>> [1] https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=efd293947f940180eedd8d0915b124f4aedccc08
>>
>> Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
> 
> Applied to master, then reverted, then applied to next, thanks.

 Ah, sorry, I forgot to add the /next part... Well, it was already late :-)

 Regards,
 Arnout

> 
> /me goes grab a third coffee before resuming patch reviews...
> 
> Regards,
> Yann E. MORIN.
> 
>> ---
>> Note: I tried updating to v1.2.53 first, but that failed due to [2]
>>
>> [2] https://bugzilla.kernel.org/show_bug.cgi?id=214023#c16
>> ---
>>  ...don-t-overwrite-empty-when-generatin.patch | 50 +++++++++++++++++++
>>  1 file changed, 50 insertions(+)
>>  create mode 100644 package/libcap/0001-libcap-Makefile-don-t-overwrite-empty-when-generatin.patch
>>
>> diff --git a/package/libcap/0001-libcap-Makefile-don-t-overwrite-empty-when-generatin.patch b/package/libcap/0001-libcap-Makefile-don-t-overwrite-empty-when-generatin.patch
>> new file mode 100644
>> index 0000000000..a47a2c788e
>> --- /dev/null
>> +++ b/package/libcap/0001-libcap-Makefile-don-t-overwrite-empty-when-generatin.patch
>> @@ -0,0 +1,50 @@
>> +From dc507a812d931c24f1ac98c811fdd29bffa21da9 Mon Sep 17 00:00:00 2001
>> +From: "Arnout Vandecappelle (Essensium/Mind)" <arnout at mind.be>
>> +Date: Tue, 24 Aug 2021 00:36:40 +0200
>> +Subject: [PATCH] libcap/Makefile: don't overwrite 'empty' when generating
>> + loader.txt
>> +
>> +objcopy takes an input file and an output file as arguments. If the
>> +output file is left out, the input file will be overwritten.
>> +
>> +Since the objcopy command used to generate loader.txt only does a
>> +dump-section and no filtering, in practice there is no change to empty.
>> +However, as a side-effect, its timestamp is updated. The timestamp of
>> +empty and of loader.txt will be more or less the same; however,
>> +loader.txt is closed just before the output file is closed, so it's
>> +possible that the timestamp of loader.txt is just a little bit earlier.
>> +If this happens, it causes loader.txt to be rebuilt later, which in turn
>> +causes a number of other object files to be rebuilt.
>> +
>> +Usually that's harmless, but it sometimes causes the rebuild to happen
>> +during 'make install'. This is particularly annoying if 'make install'
>> +is done as root, since loader.txt becomes owned by root in that case.
>> +
>> +Fix this by specifying a harmless output file: /dev/null.
>> +
>> +While we're at it, take in an upstream change that removes the redundant
>> +redirect.
>> +
>> +Fixes: ee3b25c0a877fa74d1aec88f325ac45b09963c82
>> +
>> +Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
>> +---
>> + libcap/Makefile | 2 +-
>> + 1 file changed, 1 insertion(+), 1 deletion(-)
>> +
>> +diff --git a/libcap/Makefile b/libcap/Makefile
>> +index 47cf8f4..18e4f4f 100644
>> +--- a/libcap/Makefile
>> ++++ b/libcap/Makefile
>> +@@ -105,7 +105,7 @@ empty: empty.c
>> + 	$(CC) -o $@ $<
>> + 
>> + loader.txt: empty
>> +-	$(OBJCOPY) --dump-section .interp=/dev/stdout $< > $@
>> ++	$(OBJCOPY) --dump-section .interp=$@ $< /dev/null
>> + 
>> + cap_magic.o: execable.h execable.c loader.txt
>> + 	$(CC) $(CFLAGS) $(IPATH) -DLIBRARY_VERSION=\"$(LIBTITLE)-$(VERSION).$(MINOR)\" -DSHARED_LOADER=\"$(shell cat loader.txt)\" -c execable.c -o $@
>> +-- 
>> +2.31.1
>> +
>> -- 
>> 2.31.1
>>
>