Hello all, My colleague Peter managed to use "git bisect" on the git mirror of gcc source code. The commit from a branch called "debug-early" seems like a possible point when the new behavior got introduced. We have also looked at this conversation: https://gcc.gnu.org/ml/gcc/2015-05/msg00046.html We would like to know if this work: >Shortly after the merge I'll work on a pass to prune unused decl DIEs as >we're presently creating more DIEs than mainline. This was expected, >and if I understood Jason correctly, it is ok to work on this post-merge. >However, even without such a pass, the .debug_info size difference is >reasonable: happened along with a future commit or if there is still some work pending. As I wrote, in our environment the debug_info size difference (from earlier 5.4 version of gcc) is significant that the object file size change is non-trivial with gcc 6.3.1. We appreciate any input and help. Thanks. On Thu, Jun 15, 2017 at 2:45 PM, Siva Narayanan <sinaraya@xxxxxxxxxx> wrote: > Hi, > > With a test code like so: > > struct foo { > int fooMember; > }; > > extern struct foo fooDeclared; > > void asymbol() { } > > We find that gcc6 (or even gcc7) generates a lot more debug > information. "readelf -wi <.o file>" shows the following. > > <1><2d>: Abbrev Number: 2 (DW_TAG_structure_type) > <2e> DW_AT_name : foo > <32> DW_AT_byte_size : 4 > <33> DW_AT_decl_file : 1 > <34> DW_AT_decl_line : 1 > <35> DW_AT_sibling : <0x46> > <2><39>: Abbrev Number: 3 (DW_TAG_member) > <3a> DW_AT_name : (indirect string, offset: 0xc): fooMember > <3e> DW_AT_decl_file : 1 > <3f> DW_AT_decl_line : 2 > <40> DW_AT_type : <0x46> > <44> DW_AT_data_member_location: 0 > <2><45>: Abbrev Number: 0 > <1><46>: Abbrev Number: 4 (DW_TAG_base_type) > <47> DW_AT_byte_size : 4 > <48> DW_AT_encoding : 5 (signed) > <49> DW_AT_name : int > <1><4d>: Abbrev Number: 5 (DW_TAG_variable) > <4e> DW_AT_name : (indirect string, offset: 0x0): fooDeclared > <52> DW_AT_decl_file : 1 > <53> DW_AT_decl_line : 5 > <54> DW_AT_type : <0x2d> > <58> DW_AT_external : 1 > <58> DW_AT_declaration : 1 > > The compilation line is: "gcc -o t.o -c -g t.c" in all attempts. > > It is not at all obvious why there is debug information being > generated for an unused "extern" (struct foo, "fooDeclared") > > We don't observe this with gcc4 or gcc5. In our environment this seems > to result in the non-trivial increase of object file size (on disk), > resulting in other downstream issues. > > So we are trying to understand if some config option has some how > become default. > > gcc 5.4 version, built from Fedora based sources: gcc version 5.4.0 > 20160603 (Red Hat 5.4.0-6) (GCC) - does not produce this behavior. > > gcc 6.3 version which exhibits this new behavior: gcc version 6.3.1 > 20170216 (Red Hat 6.3.1-3) (GCC). We picked the source rpm for this > from F25. > > We also tested on gcc 6.2 (Ubuntu Yakkety, and observed the same new > behavior): gcc version 6.2.0 20161005 (Ubuntu 6.2.0-5ubuntu12) > > Many thanks.
