Hi Daniel, On Friday, 16 June 2017 15:48:06 PDT Daniel Schwierzeck wrote: > Am 16.06.2017 um 02:05 schrieb Paul Burton: > > 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.bur...@imgtec.com> > > Cc: Daniel Schwierzeck <daniel.schwierz...@gmail.com> > > Cc: u-boot@lists.denx.de > > --- > > > > arch/mips/Makefile.postlink | 23 +++ > > arch/mips/config.mk | 19 +- > > arch/mips/cpu/start.S | 130 ------------- > > arch/mips/cpu/u-boot.lds | 41 +--- > > arch/mips/include/asm/relocs.h | 24 +++ > > arch/mips/lib/Makefile | 1 + > > arch/mips/lib/reloc.c | 164 ++++++++++++++++ > > common/board_f.c | 2 +- > > tools/.gitignore | 1 + > > tools/Makefile | 2 + > > tools/mips-relocs.c | 426 > > +++++++++++++++++++++++++++++++++++++++++ 11 files changed, 656 > > insertions(+), 177 deletions(-) > > create mode 100644 arch/mips/Makefile.postlink > > create mode 100644 arch/mips/include/asm/relocs.h > > create mode 100644 arch/mips/lib/reloc.c > > create mode 100644 tools/mips-relocs.c > > there is a regression on qemu_mips when started with Qemu. The code > execution hangs in an endless loop and doesn't reach the console prompt. > > I could debug it to following location: > > int bootm_find_images(int flag, int argc, char * const argv[]) > { > int ret; > > /* find ramdisk */ > ret = boot_get_ramdisk(argc, argv, &images, IH_INITRD_ARCH, > &images.rd_start, &images.rd_end); > if (ret) { > puts("Ramdisk image is corrupt or invalid\n"); > return 1; > } > ... > } > > The code flow goes into the "if (ret)" branch. At the "return 1" the $ra > register contains the address of bootm_find_images(). Thus the code is > executed in an endless loop. I don't know yet if that's a miscalculated > relocation or a stack overflow (maybe due to the changed 64KiB alignment > of the U-Boot relocation address) because $ra in bootm_find_images() is > loaded from stack: > > bfc08f1c <bootm_find_images>: > bfc08f1c: 3c02bfc3 lui v0,0xbfc3 > bfc08f20: 27bdffe0 addiu sp,sp,-32 > ... > bfc08f6c: 8fbf001c lw ra,28(sp) > bfc08f70: 00601025 move v0,v1 > bfc08f74: 03e00008 jr ra > bfc08f78: 27bd0020 addiu sp,sp,32 > > > This regression leads to broken pytest for qemu_mips and therefore to > failing Travis CI [1]. I used the kernel.org MIPS toolchain with gcc-4.9 > (same as in Travis CI). Could you please have a look? > > > [1] https://travis-ci.org/danielschwierzeck/u-boot/jobs/243667863
This was due to an R_MIPS_26 relocation applied to a j instruction in show_board_info, which overflowed into the opcode field & changed the j into a jal. v3 should fix it. Thanks, Paul
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