On 20/11/2019 15.51, Jessica Yu wrote:
We can alleviate this situation by utilizing the SHF_MERGE and
SHF_STRING section flags. SHF_MERGE|SHF_STRING indicate to the linker
that the data in the section are null-terminated strings
[pet peeve: nul, not null.]
As of v5.4-rc5, the following statistics were gathered with x86
defconfig with approximately 10.7k exported symbols.
Size of __ksymtab_strings in vmlinux:
-------------------------------------
v5.4-rc5: 213834 bytes
v5.4-rc5 with commit c3a6cf19e695: 224455 bytes
v5.4-rc5 with this patch: 205759 bytes
So, we already see memory savings of ~8kB compared to vanilla -rc5 and
savings of nearly 18.7kB compared to -rc5 with commit c3a6cf19e695 on top.
Yippee :) Thanks for picking up the ball and sending this.
/*
- * note on .section use: @progbits vs %progbits nastiness doesn't matter,
- * since we immediately emit into those sections anyway.
+ * note on .section use: we specify @progbits vs %progbits since usage of
+ * "M" (SHF_MERGE) section flag requires it.
*/
+
+#ifdef CONFIG_ARM
+#define ARCH_PROGBITS %progbits
+#else
+#define ARCH_PROGBITS @progbits
+#endif
Did you figure out a way to determine if ARM is the only odd one? I was
just going by gas' documentation which mentions ARM as an example, but
doesn't really provide a way to know what each arch uses. I suppose 0day
will tell us shortly.
If we want to avoid arch-ifdefs in these headers (and that could become
unwieldy if ARM is not the only one) I think one could add a
asm-generic/progbits.h, add progbits.h to mandatory-y in
include/asm-generic/Kbuild, and then just provide a progbits.h on ARM
(and the other exceptions) - then I think the kbuild logic automatically
makes "#include <asm/progbits.h>" pick up the right one. And the header
could define ARCH_PROGBITS with or without the double quotes depending
on __ASSEMBLY__.