[PATCH v4] meson.build: default to -gsplit-dwarf for debug info

[PATCH v4] 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
v4
  - we don't need to pass -g, due to meson doing it under the hood
  - add comment around option_cflags to make mesons roll clear
---
 meson.build                   | 6 ++++++
 meson_options.txt             | 2 ++
 scripts/meson-buildoptions.sh | 2 ++
 3 files changed, 10 insertions(+)

diff --git a/meson.build b/meson.build
index 8d0abe7f12..a8db76fccc 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') and get_option('split_debug')
+  qemu_cflags += '-gsplit-dwarf'
+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')
@@ -4589,6 +4593,8 @@ if have_rust
   summary_info += {'bindgen':         bindgen.full_path()}
   summary_info += {'bindgen version': bindgen.version()}
 endif
+# option_cflags is purely for the summary display, meson will pass
+# -g/-O options directly
 option_cflags = (get_option('debug') ? ['-g'] : [])
 if get_option('optimization') != 'plain'
   option_cflags += ['-O' + get_option('optimization')]
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 v4] meson.build: default to -gsplit-dwarf for debug info

[Paolo Bonzini]

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Il ven 7 mar 2025, 16:17 Alex Bennée <alex.bennee@linaro.org> ha scritto:

> 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>
>

Queued, thanks.

Paolo


> ---
> 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
> v4
>   - we don't need to pass -g, due to meson doing it under the hood
>   - add comment around option_cflags to make mesons roll clear
> ---
>  meson.build                   | 6 ++++++
>  meson_options.txt             | 2 ++
>  scripts/meson-buildoptions.sh | 2 ++
>  3 files changed, 10 insertions(+)
>
> diff --git a/meson.build b/meson.build
> index 8d0abe7f12..a8db76fccc 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') and get_option('split_debug')
> +  qemu_cflags += '-gsplit-dwarf'
> +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')
> @@ -4589,6 +4593,8 @@ if have_rust
>    summary_info += {'bindgen':         bindgen.full_path()}
>    summary_info += {'bindgen version': bindgen.version()}
>  endif
> +# option_cflags is purely for the summary display, meson will pass
> +# -g/-O options directly
>  option_cflags = (get_option('debug') ? ['-g'] : [])
>  if get_option('optimization') != 'plain'
>    option_cflags += ['-O' + get_option('optimization')]
> 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
>
>

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