[PATCH v3] meson.build: default to -gsplit-dwarf for debug info

[PATCH v3] meson.build: default to -gsplit-dwarf for debug info

[Alex Bennée]

This option is supported by both gcc (since 4.7) and clang (since
7.0). Not only does this make the linkers job easier by reducing the
amount of ELF it needs to parse it also reduces the total build size
quite considerably. In my case a default build went from 5.8G to
3.9G (vs 1.9G for --disable-debug-info).

The --disable-split-debug option allows distros to keep all the info
together for ease of packaging.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

---
v1
  - add --disable/enable-split-debug
  - move to option_cflags
v2
  - removed unneeded []'s
  - fix stray whitespace
v3
  - set qemu_cflags instead of option_cflags
  - move up to the rest of the qemu_cflag setting code
  - update build size numbers with --disable-debug-info
---
 meson.build                   | 6 +++++-
 meson_options.txt             | 2 ++
 scripts/meson-buildoptions.sh | 2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index 8d0abe7f12..bba17c73f1 100644
--- a/meson.build
+++ b/meson.build
@@ -601,6 +601,10 @@ if get_option('tsan')
   qemu_ldflags = ['-fsanitize=thread'] + qemu_ldflags
 endif
 
+if get_option('debug')
+  qemu_cflags += get_option('split_debug') ? ['-gsplit-dwarf'] : ['-g']
+endif
+
 # Detect support for PT_GNU_RELRO + DT_BIND_NOW.
 # The combination is known as "full relro", because .got.plt is read-only too.
 qemu_ldflags += cc.get_supported_link_arguments('-Wl,-z,relro', '-Wl,-z,now')
@@ -4589,7 +4593,7 @@ if have_rust
   summary_info += {'bindgen':         bindgen.full_path()}
   summary_info += {'bindgen version': bindgen.version()}
 endif
-option_cflags = (get_option('debug') ? ['-g'] : [])
+option_cflags = []
 if get_option('optimization') != 'plain'
   option_cflags += ['-O' + get_option('optimization')]
 endif
diff --git a/meson_options.txt b/meson_options.txt
index 59d973bca0..3432123fee 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -362,6 +362,8 @@ option('debug_mutex', type: 'boolean', value: false,
        description: 'mutex debugging support')
 option('debug_stack_usage', type: 'boolean', value: false,
        description: 'measure coroutine stack usage')
+option('split_debug', type: 'boolean', value: true,
+       description: 'split debug info from object files')
 option('qom_cast_debug', type: 'boolean', value: true,
        description: 'cast debugging support')
 option('slirp_smbd', type : 'feature', value : 'auto',
diff --git a/scripts/meson-buildoptions.sh b/scripts/meson-buildoptions.sh
index 3e8e00852b..aca6e68830 100644
--- a/scripts/meson-buildoptions.sh
+++ b/scripts/meson-buildoptions.sh
@@ -504,6 +504,8 @@ _meson_option_parse() {
     --disable-strict-rust-lints) printf "%s" -Dstrict_rust_lints=false ;;
     --enable-strip) printf "%s" -Dstrip=true ;;
     --disable-strip) printf "%s" -Dstrip=false ;;
+    --enable-split-debug) printf "%s" -Dsplit_debug=true ;;
+    --disable-split-debug) printf "%s" -Dsplit_debug=false ;;
     --sysconfdir=*) quote_sh "-Dsysconfdir=$2" ;;
     --enable-tcg) printf "%s" -Dtcg=enabled ;;
     --disable-tcg) printf "%s" -Dtcg=disabled ;;
-- 
2.39.5

Re: [PATCH v3] meson.build: default to -gsplit-dwarf for debug info

[Paolo Bonzini]

On Thu, Mar 6, 2025 at 5:16 PM Alex Bennée <alex.bennee@linaro.org> wrote:
> +if get_option('debug')
> +  qemu_cflags += get_option('split_debug') ? ['-gsplit-dwarf'] : ['-g']
> +endif

Since -g is already added by meson, it's enough to do

-if get_option('debug')
-  qemu_cflags += get_option('split_debug') ? ['-gsplit-dwarf'] : ['-g']
+if get_option('debug') and get_option('split_debug')
+  qemu_cflags += '-gsplit-dwarf'
 endif

Applied with this change, then.

Paolo

Re: [PATCH v3] meson.build: default to -gsplit-dwarf for debug info

[Alex Bennée]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On Thu, Mar 6, 2025 at 5:16 PM Alex Bennée <alex.bennee@linaro.org> wrote:
>> +if get_option('debug')
>> +  qemu_cflags += get_option('split_debug') ? ['-gsplit-dwarf'] : ['-g']
>> +endif
>
> Since -g is already added by meson, it's enough to do
>
> -if get_option('debug')
> -  qemu_cflags += get_option('split_debug') ? ['-gsplit-dwarf'] : ['-g']
> +if get_option('debug') and get_option('split_debug')
> +  qemu_cflags += '-gsplit-dwarf'
>  endif
>
> Applied with this change, then.

Ahh I guess I was missing that meson does that under the hood. Can I
have a r-b with that change or do do you want to wait for v4?


>
> Paolo

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro