seen building the gsequencer package. the warning was not emitted with gcc-10 branch 20210110, but is emitted with 20210228, also emitted with trunk 20210220. $ cat ags_midi_buffer_util.i long ags_midi_buffer_util_seek_message_delta_time; int ags_midi_buffer_util_seek_message_i; int ags_midi_buffer_util_get_varlength() { return 0; } char ags_midi_buffer_util_seek_message() { long current_delta_time; for (; ags_midi_buffer_util_seek_message_i; ags_midi_buffer_util_seek_message_i++) { ags_midi_buffer_util_get_varlength(¤t_delta_time); ags_midi_buffer_util_seek_message_delta_time = current_delta_time; } return 0; } $ gcc -std=gnu99 -Wall -Werror=maybe-uninitialized -fstack-protector-strong -fPIE -O1 -c ags_midi_buffer_util.i ags_midi_buffer_util.i: In function 'ags_midi_buffer_util_seek_message': ags_midi_buffer_util.i:5:8: error: 'current_delta_time' may be used uninitialized in this function [-Werror=maybe-uninitialized] 5 | long current_delta_time; | ^~~~~~~~~~~~~~~~~~ cc1: some warnings being treated as errors
I see the warning (with -fPIE) for all releases I have (4.8.0+). But yes, -fPIC does not report the warning.
PIC allows interposing ags_midi_buffer_util_get_varlength and thus possibly initializing the argument. PIE does not allow this so we see it is not initialized. I suppose the change on the branch is for some unreduced testcase where different optimization might trigger the new warning (correctly I think).
Created attachment 50284 [details] preprocessed source original test case before reducing gcc -std=gnu99 -Werror=uninitialized -Werror=maybe-uninitialized -Wall -Wno-unused-variable -Wno-unused-but-set-variable -Wformat -Wno-pointer-sign -Werror=format-security -fstack-protector-strong -fPIC -O2 -c ags_midi_buffer_util_orig.i
(In reply to Matthias Klose from comment #3) > Created attachment 50284 [details] > preprocessed source > > original test case before reducing > > gcc -std=gnu99 -Werror=uninitialized -Werror=maybe-uninitialized -Wall > -Wno-unused-variable -Wno-unused-but-set-variable -Wformat -Wno-pointer-sign > -Werror=format-security -fstack-protector-strong -fPIC -O2 -c > ags_midi_buffer_util_orig.i Using this with -fPIE reports the warning only on gcc-10 branch. All other is fine.
Started on gcc-10 branch with g:eddcb627ccfbd97e025cf366cc3f3bad76211785. Anyway, the warning contains quite some false positives..
GCC 9 warns as well. I think this was a false negative which is now fixed. Note GCC 10.1.0 and GCC 10.2.0 warn for me as well, so something must have regressed this between 10.2.0 and g:eddcb627ccfbd97e025cf366 I'm inclined to mark as INVALID.
The IL with -fPIC shows a call to ags_midi_buffer_util_get_varlength() while the IL with -fPIE has the call expanded inline, which is what less the warning see current_delta_time is not initialized. With that, resolving as invalid per c6.