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Add a --split-dwarf option to configure.py

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It is off by default as it conflicts with distcc.

Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
Message-Id: <20190204002706.15540-1-espindola@scylladb.com>
This commit is contained in:
Rafael Ávila de Espíndola
2019-02-03 16:27:06 -08:00
committed by Avi Kivity
parent a9e1e0233a
commit bbd9dfcba7
2 changed files with 23 additions and 1 deletions
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20
HACKING.md
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@@ -288,7 +288,7 @@ In this example, `10.0.0.2` will be sent up to 16 jobs and the local machine wil
When a compilation is in progress, the status of jobs on all remote machines can be visualized in the terminal with `distccmon-text` or graphically as a GTK application with `distccmon-gnome`.
One thing to keep in mind is that linking object files happens on the coordinating machine, which can be a bottleneck. See the next section speeding up this process.
One thing to keep in mind is that linking object files happens on the coordinating machine, which can be a bottleneck. See the next sections speeding up this process.
### Using the `gold` linker
@@ -298,6 +298,24 @@ Linking Scylla can be slow. The gold linker can replace GNU ld and often speeds
$ sudo alternatives --config ld
```
### Using split dwarf
With debug info enabled, most of the link time is spent copying and
relocating it. It is possible to leave most of the debug info out of
the link by writing it to a side .dwo file. This is done by passing
`-gsplit-dwarf` to gcc.
Unfortunately just `-gsplit-dwarf` would slow down `gdb` startup. To
avoid that the gold linker can be told to create an index with
`--gdb-index`.
More info at https://gcc.gnu.org/wiki/DebugFission.
Both options can be enable by passing `--split-dwarf` to configure.py.
Note that distcc is *not* compatible with it, but icecream
(https://github.com/icecc/icecream) is.
### Testing changes in Seastar with Scylla
Sometimes Scylla development is closely tied with a feature being developed in Seastar. It can be useful to compile Scylla with a particular check-out of Seastar.

4
configure.py
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@@ -433,6 +433,8 @@ arg_parser.add_argument('--python', action='store', dest='python', default='pyth
help='Python3 path')
add_tristate(arg_parser, name='hwloc', dest='hwloc', help='hwloc support')
add_tristate(arg_parser, name='xen', dest='xen', help='Xen support')
arg_parser.add_argument('--split-dwarf', dest='split_dwarf', action='store_true', default=False,
help='use of split dwarf (https://gcc.gnu.org/wiki/DebugFission) to speed up linking')
arg_parser.add_argument('--enable-gcc6-concepts', dest='gcc6_concepts', action='store_true', default=False,
help='enable experimental support for C++ Concepts as implemented in GCC 6')
arg_parser.add_argument('--enable-alloc-failure-injector', dest='alloc_failure_injector', action='store_true', default=False,
@@ -1030,6 +1032,8 @@ if args.gcc6_concepts:
seastar_flags += ['--enable-gcc6-concepts']
if args.alloc_failure_injector:
seastar_flags += ['--enable-alloc-failure-injector']
if args.split_dwarf:
seastar_flags += ['--split-dwarf']
debug_flags = ' ' + debug_compress_flag(compiler=args.cxx) + ' ' + dbgflag
modes['debug']['opt'] += debug_flags