Am 04.03.19 um 20:05 schrieb Peter Mamonov: > Hi, Oleksij, > > On Mon, Feb 18, 2019 at 08:52:00AM +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> >> --- >> >> [...] >> >> diff --git a/arch/mips/Makefile b/arch/mips/Makefile >> index 5fbd51ceee..5eccf18fe4 100644 >> --- a/arch/mips/Makefile >> +++ b/arch/mips/Makefile >> @@ -11,7 +11,7 @@ endif >> >> CPPFLAGS += -D__MIPS__ -fno-strict-aliasing -fno-merge-constants >> >> -cflags-y += -G 0 -mno-abicalls -fno-pic -pipe >> +cflags-y += -G 0 -mno-abicalls -pipe > > The patch you've ported from das u-boot removes `-fpic` flag, yet your patch > removes `-fno-pic`, i.e. it does the opposite thing. Good point, this part of the change has no influence. With or without this flag, noPIC code is build. I'll put it back to avoid confusion. -- Regards, Oleksij
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