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Use -ffunction-sections to build smaller binaries #8658

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@rustyrussell rustyrussell commented Nov 4, 2025

This gives us a 20% reduction in in-memory sizes for non-Rust binaries.

@rustyrussell
Makefile: improve print-binary-sizes to be more meaningful.
d7a7e1c 
Users care about memory more than disk, and they care about programs
they run more than our test programs and tools.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
@rustyrussell rustyrussell added this to the v25.12 milestone Nov 4, 2025
@rustyrussell
Build: add function sections.
38635c0 
This allows further reduction in binary sizes.

Size of all user before:
	   text		   data	    bss	    dec		    hex	filename
	64277932	 904968	 317576	65500476	3e7753c	(TOTALS)

After:
	52443036	 729560	 271720	53444316	32f7edc	(TOTALS)

Some are dramatic, such as lightning-cli not pulling in libbacktrace:

 174454	   2880	    296	 177630	  2b5de	cli/lightning-cli
  56633	   2608	    232	  59473	   e851	cli/lightning-cli

But most things get a 25% trim:

3972339	 363568	  21760	4357667	 427e23	lightningd/lightningd
3300337	 247768	  21664	3569769	 367869	lightningd/lightningd

Changelog-Changed: Build: most binaries are now about 20% smaller.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
@rustyrussell rustyrussell force-pushed the guilt/try-function-sections branch from 73d7607 to 38635c0 Compare November 4, 2025 02:28
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Lagrang3 commented Nov 4, 2025

If I don't build manually tools/lightning-hsmtool I get the following error

$ uv run make print-binary-sizes
User programs:
   text	   data	    bss	    dec	    hex	filename
2207578	   6736	   4928	2219242	 21dcea	lightningd/lightning_channeld
...
 180194	   2840	    296	 183330	  2cc22	cli/lightning-cli
4015976	 363400	  21760	4401136	 4327f0	lightningd/lightningd
size: 'tools/lightning-hsmtool': No such file
2057558	   6344	   4768	2068670	 1f90be	plugins/autoclean
...
2186875	   9280	   4704	2200859	 21951b	plugins/bookkeeper
177776820	5769632	 322872	183869324	af59f8c	(TOTALS)
make: *** [Makefile:1111: print-binary-sizes] Error 1

The problem is that ALL_PROGRAMS contain tools/hsmtool but not tools/lightning-hsmtool.
The latter is instead found in BIN_PROGRAMS and it is a dependency of the make install target.
A fix could be to make print-binary-sizes dependent on BIN_PROGRAMS as well.

diff --git a/Makefile b/Makefile
index 5c93e6145..4798fc59d 100644
--- a/Makefile
+++ b/Makefile
@@ -1106,7 +1106,7 @@ ccan-rune-rune.o: $(CCANDIR)/ccan/rune/rune.c
 ccan-rune-coding.o: $(CCANDIR)/ccan/rune/coding.c
        @$(call VERBOSE, "cc $<", $(CC) $(CFLAGS) -c -o $@ $<)
 
-print-binary-sizes: $(ALL_PROGRAMS) $(ALL_TEST_PROGRAMS)
+print-binary-sizes: $(ALL_PROGRAMS) $(ALL_TEST_PROGRAMS) $(BIN_PROGRAMS)
        @echo User programs:
        @size -t $(PKGLIBEXEC_PROGRAMS) $(filter-out tools/reckless,$(BIN_PROGRAMS)) $(PLUGINS)
        @echo All programs:

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@rustyrussell @Lagrang3