From 28ed10d6a67c9f674e827dafc4bab173445c626b Mon Sep 17 00:00:00 2001 From: Oleksij Rempel Date: Wed, 10 Apr 2019 09:04:40 +0200 Subject: MIPS: relocation: add relocation support 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 | | 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 Signed-off-by: Oleksij Rempel Signed-off-by: Sascha Hauer --- arch/mips/lib/reloc.c | 182 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 182 insertions(+) create mode 100644 arch/mips/lib/reloc.c (limited to 'arch/mips/lib/reloc.c') diff --git a/arch/mips/lib/reloc.c b/arch/mips/lib/reloc.c new file mode 100644 index 0000000000..9756d61666 --- /dev/null +++ b/arch/mips/lib/reloc.c @@ -0,0 +1,182 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * MIPS Relocation + * + * Copyright (c) 2017 Imagination Technologies Ltd. + * + * Relocation data, found in the .rel section, is generated by the mips-relocs + * tool & contains a record of all locations in the Barebox binary that need to + * be fixed up during relocation. + * + * The data is a sequence of unsigned integers, which are of somewhat arbitrary + * size. This is achieved by encoding integers as a sequence of bytes, each of + * which contains 7 bits of data with the most significant bit indicating + * whether any further bytes need to be read. The least significant bits of the + * integer are found in the first byte - ie. it somewhat resembles little + * endian. + * + * Each pair of two integers represents a relocation that must be applied. The + * first integer represents the type of relocation as a standard ELF relocation + * type (ie. R_MIPS_*). The second integer represents the offset at which to + * apply the relocation, relative to the previous relocation or for the first + * relocation the start of the relocated .text section. + * + * The end of the relocation data is indicated when type R_MIPS_NONE (0) is + * read, at which point no further integers should be read. That is, the + * terminating R_MIPS_NONE reloc includes no offset. + */ + +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#define MAX_BSS_SIZE SZ_1M + +void main_entry(void *fdt, u32 fdt_size); +void relocate_code(void *fdt, u32 fdt_size, u32 relocaddr); + +/** + * read_uint() - Read an unsigned integer from the buffer + * @buf: pointer to a pointer to the reloc buffer + * + * Read one whole unsigned integer from the relocation data pointed to by @buf, + * advancing @buf past the bytes encoding the integer. + * + * Returns: the integer read from @buf + */ +static unsigned long read_uint(uint8_t **buf) +{ + unsigned long val = 0; + unsigned int shift = 0; + uint8_t new; + + do { + new = *(*buf)++; + val |= (new & 0x7f) << shift; + shift += 7; + } while (new & 0x80); + + return val; +} + +/** + * apply_reloc() - Apply a single relocation + * @type: the type of reloc (R_MIPS_*) + * @addr: the address that the reloc should be applied to + * @off: the relocation offset, ie. number of bytes we're moving Barebox by + * + * Apply a single relocation of type @type at @addr. This function is + * intentionally simple, and does the bare minimum needed to fixup the + * relocated Barebox - in particular, it does not check for overflows. + */ +static void apply_reloc(unsigned int type, void *addr, long off) +{ + uint32_t u32; + + switch (type) { + case R_MIPS_26: + u32 = *(uint32_t *)addr; + u32 = (u32 & GENMASK(31, 26)) | + ((u32 + (off >> 2)) & GENMASK(25, 0)); + *(uint32_t *)addr = u32; + break; + + case R_MIPS_32: + *(uint32_t *)addr += off; + break; + + case R_MIPS_64: + *(uint64_t *)addr += off; + break; + + case R_MIPS_HI16: + *(uint32_t *)addr += off >> 16; + break; + + default: + panic("Unhandled reloc type %u\n", type); + } +} + +/** + * relocate_code() - Relocate Barebox, generally from flash to DDR + * @start_addr_sp: new stack pointer + * @new_gd: pointer to relocated global data + * @relocaddr: the address to relocate to + * + * Relocate Barebox from its current location (generally in flash) to a new one + * (generally in DDR). This function will copy the Barebox binary & apply + * relocations as necessary, then jump to board_init_r in the new build of + * Barebox. As such, this function does not return. + */ +void relocate_code(void *fdt, u32 fdt_size, u32 ram_size) +{ + unsigned long addr, length, bss_len; + u32 relocaddr, new_stack; + uint8_t *buf, *bss_start; + unsigned int type; + long off; + + length = barebox_image_size + MAX_BSS_SIZE; + relocaddr = ALIGN_DOWN(ram_size - barebox_image_size, SZ_64K); + relocaddr = KSEG0ADDR(relocaddr); + new_stack = relocaddr - MALLOC_SIZE - 16; + + /* + * Ensure that we're relocating by an offset which is a multiple of + * 64KiB, ie. doesn't change the least significant 16 bits of any + * addresses. This allows us to discard R_MIPS_LO16 relocs, saving + * space in the Barebox binary & complexity in handling them. + */ + off = relocaddr - (unsigned long)__image_start; + if (off & 0xffff) + panic("Mis-aligned relocation\n"); + + /* Copy Barebox to RAM */ + memcpy((void *)relocaddr, __image_start, length); + + /* Now apply relocations to the copy in RAM */ + buf = __rel_start; + addr = relocaddr; + while (true) { + type = read_uint(&buf); + if (type == R_MIPS_NONE) + break; + + addr += read_uint(&buf) << 2; + apply_reloc(type, (void *)addr, off); + } + + /* Ensure the icache is coherent */ + flush_cache_all(); + + /* Clear the .bss section */ + bss_start = (uint8_t *)((unsigned long)__bss_start + off); + bss_len = (unsigned long)&__bss_stop - (unsigned long)__bss_start; + memset(bss_start, 0, bss_len); + + __asm__ __volatile__ ( + "move $a0, %0\n" + " move $a1, %1\n" + " move $31, $0\n" + " move $sp, %2\n" + " jr %3\n" + : /* no outputs */ + : "r"(fdt), + "r"(fdt_size), + "r"(new_stack), + "r"((unsigned long)main_entry + off)); + + /* Since we jumped to the new Barebox above, we won't get here */ + unreachable(); +} -- cgit v1.2.3