On Fri, Mar 08, 2019 at 11:58:52AM +0100, Oleksij Rempel wrote: > From: Oleksij Rempel <linux@xxxxxxxxxxxxxxxx> > > this patch i a port of following patch from u-boot with some additional > integration changes and fixes of original code: > | Subject: [PATCH] MIPS: Stop building position independent code > | > | U-Boot has up until now built with -fpic for the MIPS architecture, > | producing position independent code which uses indirection through a > | global offset table, making relocation fairly straightforward as it > | simply involves patching up GOT entries. > | > | Using -fpic does however have some downsides. The biggest of these is > | that generated code is bloated in various ways. For example, function > | calls are indirected through the GOT & the t9 register: > | > | 8f998064 lw t9,-32668(gp) > | 0320f809 jalr t9 > | > | Without -fpic the call is simply: > | > | 0f803f01 jal be00fc04 <puts> > | > | This is more compact & faster (due to the lack of the load & the > | dependency the jump has on its result). It is also easier to read & > | debug because the disassembly shows what function is being called, > | rather than just an offset from gp which would then have to be looked up > | in the ELF to discover the target function. > | > | Another disadvantage of -fpic is that each function begins with a > | sequence to calculate the value of the gp register, for example: > | > | 3c1c0004 lui gp,0x4 > | 279c3384 addiu gp,gp,13188 > | 0399e021 addu gp,gp,t9 > | > | Without using -fpic this sequence no longer appears at the start of each > | function, reducing code size considerably. > | > | This patch switches U-Boot from building with -fpic to building with > | -fno-pic, in order to gain the benefits described above. The cost of > | this is an extra step during the build process to extract relocation > | data from the ELF & write it into a new .rel section in a compact > | format, plus the added complexity of dealing with multiple types of > | relocation rather than the single type that applied to the GOT. The > | benefit is smaller, cleaner, more debuggable code. The relocate_code() > | function is reimplemented in C to handle the new relocation scheme, > | which also makes it easier to read & debug. > | > | Taking maltael_defconfig as an example the size of u-boot.bin built > | using the Codescape MIPS 2016.05-06 toolchain (gcc 4.9.2, binutils > | 2.24.90) shrinks from 254KiB to 224KiB. > | > | Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx> > > Signed-off-by: Oleksij Rempel <linux@xxxxxxxxxxxxxxxx> > --- > arch/mips/Kconfig | 18 ++ > arch/mips/Makefile | 9 +- > arch/mips/boot/main_entry-pbl.c | 4 +- > arch/mips/boot/start.S | 4 +- > arch/mips/include/asm/relocs.h | 23 ++ > arch/mips/include/asm/sections.h | 14 + > arch/mips/lib/Makefile | 2 + > arch/mips/lib/barebox.lds.S | 27 +- > arch/mips/lib/reloc.c | 182 +++++++++++++ > arch/mips/lib/sections.c | 9 + > scripts/Makefile | 1 + > scripts/mips-relocs.c | 426 +++++++++++++++++++++++++++++++ > 12 files changed, 712 insertions(+), 7 deletions(-) > create mode 100644 arch/mips/include/asm/relocs.h > create mode 100644 arch/mips/lib/reloc.c > create mode 100644 arch/mips/lib/sections.c > create mode 100644 scripts/mips-relocs.c > > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig > index eab9452de9..49f238df58 100644 > --- a/arch/mips/Kconfig > +++ b/arch/mips/Kconfig > @@ -32,6 +32,24 @@ config PHYS_ADDR_T_64BIT > > menu "Machine selection" > > +config MIPS_RELOCATION_TABLE_SIZE > + hex "Relocation table size" > + range 0x100 0x10000 > + default "0x8000" > + ---help--- > + A table of relocation data will be appended to the Barebox binary > + and parsed in relocate_code() to fix up all offsets in the relocated > + Barebox. > + > + This option allows the amount of space reserved for the table to be > + adjusted in a range from 256 up to 64k. The default is 32k and should > + be ok in most cases. Reduce this value to shrink the size of U-Boot > + binary. > + > + The build will fail and a valid size suggested if this is too small. > + > + If unsure, leave at the default value. > + > config BUILTIN_DTB > bool "link a DTB into the barebox image" > depends on OFTREE > diff --git a/arch/mips/Makefile b/arch/mips/Makefile > index 5fbd51ceee..7830f44be4 100644 > --- a/arch/mips/Makefile > +++ b/arch/mips/Makefile > @@ -59,7 +59,7 @@ CPPFLAGS += -DTEXT_BASE=$(CONFIG_TEXT_BASE) > ifndef CONFIG_MODULES > # Add cleanup flags > CPPFLAGS += -fdata-sections -ffunction-sections > -LDFLAGS_barebox += -static --gc-sections > +LDFLAGS_barebox += -static --gc-sections --emit-relocs > endif > > ifdef CONFIG_IMAGE_COMPRESSION > @@ -116,6 +116,13 @@ CFLAGS += $(cflags-y) > > lds-$(CONFIG_GENERIC_LINKER_SCRIPT) := arch/mips/lib/barebox.lds > > +cmd_barebox__ ?= $(LD) $(LDFLAGS) $(LDFLAGS_barebox) -o $@ \ > + -T $(barebox-lds) \ > + --start-group $(barebox-common) --end-group \ > + $(filter-out $(barebox-lds) $(barebox-common) FORCE ,$^); \ > + $(srctree)/scripts/mips-relocs $@ This should be $(objtree), otherwise it breaks out of tree build. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
