Message ID | 1463000807-18015-4-git-send-email-rjones@redhat.com |
---|---|
State | New |
Headers | show |
On 11/05/2016 23:06, Richard W.M. Jones wrote: > From: Marc Marí <markmb@redhat.com> > > This optionrom is based on linuxboot.S. > > Signed-off-by: Marc Marí <markmb@redhat.com> > Signed-off-by: Richard W.M. Jones <rjones@redhat.com> Hmm, I hadn't noticed that you added -m16. That breaks on even not-too-old GCC (such as 4.8 on RHEL/CentOS 7). Can you add some Makefile logic to switch between "-m16" and a "-include code16gcc.h" that only contains 'asm(".code16gcc");'? Also, you need to add linuxboot_dma.bin after linuxboot.bin in the main Makefile. Thanks, Paolo > --- > .gitignore | 4 + > hw/i386/pc.c | 10 +- > hw/nvram/fw_cfg.c | 2 +- > include/hw/nvram/fw_cfg.h | 1 + > pc-bios/optionrom/Makefile | 13 +- > pc-bios/optionrom/linuxboot_dma.c | 291 ++++++++++++++++++++++++++++++++++++++ > 6 files changed, 316 insertions(+), 5 deletions(-) > create mode 100644 pc-bios/optionrom/linuxboot_dma.c > > diff --git a/.gitignore b/.gitignore > index 88a80ff..101d1e0 100644 > --- a/.gitignore > +++ b/.gitignore > @@ -94,6 +94,10 @@ > /pc-bios/optionrom/linuxboot.bin > /pc-bios/optionrom/linuxboot.raw > /pc-bios/optionrom/linuxboot.img > +/pc-bios/optionrom/linuxboot_dma.asm > +/pc-bios/optionrom/linuxboot_dma.bin > +/pc-bios/optionrom/linuxboot_dma.raw > +/pc-bios/optionrom/linuxboot_dma.img > /pc-bios/optionrom/multiboot.asm > /pc-bios/optionrom/multiboot.bin > /pc-bios/optionrom/multiboot.raw > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index 99437e0..098d571 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -999,8 +999,13 @@ static void load_linux(PCMachineState *pcms, > fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_SIZE, setup_size); > fw_cfg_add_bytes(fw_cfg, FW_CFG_SETUP_DATA, setup, setup_size); > > - option_rom[nb_option_roms].name = "linuxboot.bin"; > - option_rom[nb_option_roms].bootindex = 0; > + if (fw_cfg_dma_enabled(fw_cfg)) { > + option_rom[nb_option_roms].name = "linuxboot_dma.bin"; > + option_rom[nb_option_roms].bootindex = 0; > + } else { > + option_rom[nb_option_roms].name = "linuxboot.bin"; > + option_rom[nb_option_roms].bootindex = 0; > + } > nb_option_roms++; > } > > @@ -1263,6 +1268,7 @@ void xen_load_linux(PCMachineState *pcms) > load_linux(pcms, fw_cfg); > for (i = 0; i < nb_option_roms; i++) { > assert(!strcmp(option_rom[i].name, "linuxboot.bin") || > + !strcmp(option_rom[i].name, "linuxboot_dma.bin") || > !strcmp(option_rom[i].name, "multiboot.bin")); > rom_add_option(option_rom[i].name, option_rom[i].bootindex); > } > diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c > index 999f480..114aea8 100644 > --- a/hw/nvram/fw_cfg.c > +++ b/hw/nvram/fw_cfg.c > @@ -551,7 +551,7 @@ static bool is_version_1(void *opaque, int version_id) > return version_id == 1; > } > > -static bool fw_cfg_dma_enabled(void *opaque) > +bool fw_cfg_dma_enabled(void *opaque) > { > FWCfgState *s = opaque; > > diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h > index d008112..5c27a1f 100644 > --- a/include/hw/nvram/fw_cfg.h > +++ b/include/hw/nvram/fw_cfg.h > @@ -182,5 +182,6 @@ FWCfgState *fw_cfg_init_mem_wide(hwaddr ctl_addr, > hwaddr dma_addr, AddressSpace *dma_as); > > FWCfgState *fw_cfg_find(void); > +bool fw_cfg_dma_enabled(void *opaque); > > #endif > diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile > index ce4852a..a51dd6e 100644 > --- a/pc-bios/optionrom/Makefile > +++ b/pc-bios/optionrom/Makefile > @@ -13,15 +13,24 @@ CFLAGS := -Wall -Wstrict-prototypes -Werror -fomit-frame-pointer -fno-builtin > CFLAGS += -I$(SRC_PATH) > CFLAGS += $(call cc-option, $(CFLAGS), -fno-stack-protector) > CFLAGS += $(CFLAGS_NOPIE) > +CFLAGS += -m16 > QEMU_CFLAGS = $(CFLAGS) > > -build-all: multiboot.bin linuxboot.bin kvmvapic.bin > +ASFLAGS += -32 > + > +build-all: multiboot.bin linuxboot.bin linuxboot_dma.bin kvmvapic.bin > > # suppress auto-removal of intermediate files > .SECONDARY: > > +ifdef CONFIG_WIN32 > +LD_EMULATION = i386pe > +else > +LD_EMULATION = elf_i386 > +endif > + > %.img: %.o > - $(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -Ttext 0 -e _start -s -o $@ $<," Building $(TARGET_DIR)$@") > + $(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -m $(LD_EMULATION) -Ttext 0 -e _start -s -o $@ $<," Building $(TARGET_DIR)$@") > > %.raw: %.img > $(call quiet-command,$(OBJCOPY) -O binary -j .text $< $@," Building $(TARGET_DIR)$@") > diff --git a/pc-bios/optionrom/linuxboot_dma.c b/pc-bios/optionrom/linuxboot_dma.c > new file mode 100644 > index 0000000..8ebc480 > --- /dev/null > +++ b/pc-bios/optionrom/linuxboot_dma.c > @@ -0,0 +1,291 @@ > +/* > + * Linux Boot Option ROM for fw_cfg DMA > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License as published by > + * the Free Software Foundation; either version 2 of the License, or > + * (at your option) any later version. > + * > + * This program is distributed in the hope that it will be useful, > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > + * GNU General Public License for more details. > + * > + * You should have received a copy of the GNU General Public License > + * along with this program; if not, see <http://www.gnu.org/licenses/>. > + * > + * Copyright (c) 2015-2016 Red Hat Inc. > + * Authors: > + * Marc Marí <markmb@redhat.com> > + * Richard W.M. Jones <rjones@redhat.com> > + */ > + > +asm( > +".text\n" > +".global _start\n" > +"_start:\n" > +" .short 0xaa55\n" > +" .byte 0\n" /* size in 512 units, filled in by signrom.py */ > +" .byte 0xcb\n" /* far return without prefix */ > +" .org 0x18\n" > +" .short 0\n" > +" .short _pnph\n" > +"_pnph:\n" > +" .ascii \"$PnP\"\n" > +" .byte 0x01\n" > +" .byte (_pnph_len / 16)\n" > +" .short 0x0000\n" > +" .byte 0x00\n" > +" .byte 0x00\n" > +" .long 0x00000000\n" > +" .short _manufacturer\n" > +" .short _product\n" > +" .long 0x00000000\n" > +" .short 0x0000\n" > +" .short 0x0000\n" > +" .short _bev\n" > +" .short 0x0000\n" > +" .short 0x0000\n" > +" .equ _pnph_len, . - _pnph\n" > +"_manufacturer:\n" > +" .asciz \"QEMU\"\n" > +"_product:\n" > +" .asciz \"Linux loader DMA\"\n" > +" .align 4, 0\n" > +"_bev:\n" > +" cli\n" > +" cld\n" > +" jmp load_kernel\n" > +); > + > +#include "../../include/hw/nvram/fw_cfg_keys.h" > + > +/* QEMU_CFG_DMA_CONTROL bits */ > +#define BIOS_CFG_DMA_CTL_ERROR 0x01 > +#define BIOS_CFG_DMA_CTL_READ 0x02 > +#define BIOS_CFG_DMA_CTL_SKIP 0x04 > +#define BIOS_CFG_DMA_CTL_SELECT 0x08 > + > +#define BIOS_CFG_DMA_ADDR_HIGH 0x514 > +#define BIOS_CFG_DMA_ADDR_LOW 0x518 > + > +#define uint64_t unsigned long long > +#define uint32_t unsigned int > +#define uint16_t unsigned short > + > +#define barrier() asm("" : : : "memory") > + > +typedef struct FWCfgDmaAccess { > + uint32_t control; > + uint32_t length; > + uint64_t address; > +} __attribute__((packed)) FWCfgDmaAccess; > + > +static inline void outl(uint32_t value, uint16_t port) > +{ > + asm("outl %0, %w1" : : "a"(value), "Nd"(port)); > +} > + > +static inline void set_es(void *addr) > +{ > + uint32_t seg = (uint32_t)addr >> 4; > + asm("movl %0, %%es" : : "r"(seg)); > +} > + > +#ifdef __clang__ > +#define ADDR32 > +#else > +#define ADDR32 "addr32 " > +#endif > + > +static inline uint16_t readw_es(uint16_t offset) > +{ > + uint16_t val; > + asm(ADDR32 "movw %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset)); > + barrier(); > + return val; > +} > + > +static inline uint32_t readl_es(uint16_t offset) > +{ > + uint32_t val; > + asm(ADDR32 "movl %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset)); > + barrier(); > + return val; > +} > + > +static inline void writel_es(uint16_t offset, uint32_t val) > +{ > + barrier(); > + asm(ADDR32 "movl %0, %%es:(%1)" : : "r"(val), "r"((uint32_t)offset)); > +} > + > +static inline uint32_t bswap32(uint32_t x) > +{ > + return > + ((x & 0x000000ffU) << 24) | > + ((x & 0x0000ff00U) << 8) | > + ((x & 0x00ff0000U) >> 8) | > + ((x & 0xff000000U) >> 24); > +} > + > +static inline uint64_t bswap64(uint64_t x) > +{ > + return > + ((x & 0x00000000000000ffULL) << 56) | > + ((x & 0x000000000000ff00ULL) << 40) | > + ((x & 0x0000000000ff0000ULL) << 24) | > + ((x & 0x00000000ff000000ULL) << 8) | > + ((x & 0x000000ff00000000ULL) >> 8) | > + ((x & 0x0000ff0000000000ULL) >> 24) | > + ((x & 0x00ff000000000000ULL) >> 40) | > + ((x & 0xff00000000000000ULL) >> 56); > +} > + > +static inline uint64_t cpu_to_be64(uint64_t x) > +{ > + return bswap64(x); > +} > + > +static inline uint32_t cpu_to_be32(uint32_t x) > +{ > + return bswap32(x); > +} > + > +static inline uint32_t be32_to_cpu(uint32_t x) > +{ > + return bswap32(x); > +} > + > +static void bios_cfg_read_entry(void *buf, uint16_t entry, uint32_t len) > +{ > + FWCfgDmaAccess access; > + uint32_t control = (entry << 16) | BIOS_CFG_DMA_CTL_SELECT > + | BIOS_CFG_DMA_CTL_READ; > + > + access.address = cpu_to_be64((uint64_t)(uint32_t)buf); > + access.length = cpu_to_be32(len); > + access.control = cpu_to_be32(control); > + > + barrier(); > + > + outl(cpu_to_be32((uint32_t)&access), BIOS_CFG_DMA_ADDR_LOW); > + > + while (be32_to_cpu(access.control) & ~BIOS_CFG_DMA_CTL_ERROR) { > + barrier(); > + } > +} > + > +/* Return top of memory using BIOS function E801. */ > +static uint32_t get_e801_addr(void) > +{ > + uint16_t ax, bx, cx, dx; > + uint32_t ret; > + > + asm("int $0x15\n" > + : "=a"(ax), "=b"(bx), "=c"(cx), "=d"(dx) > + : "a"(0xe801), "b"(0), "c"(0), "d"(0)); > + > + /* Not SeaBIOS, but in theory a BIOS could return CX=DX=0 in which > + * case we need to use the result from AX & BX instead. > + */ > + if (cx == 0 && dx == 0) { > + cx = ax; > + dx = bx; > + } > + > + if (dx) { > + /* DX = extended memory above 16M, in 64K units. > + * Convert it to bytes and return. > + */ > + ret = ((uint32_t)dx + 256 /* 16M in 64K units */) << 16; > + } else { > + /* This is a fallback path for machines with <= 16MB of RAM, > + * which probably would never be the case, but deal with it > + * anyway. > + * > + * CX = extended memory between 1M and 16M, in kilobytes > + * Convert it to bytes and return. > + */ > + ret = ((uint32_t)cx + 1024 /* 1M in K */) << 10; > + } > + > + return ret; > +} > + > +void load_kernel(void) > +{ > + void *setup_addr; > + void *initrd_addr; > + void *kernel_addr; > + void *cmdline_addr; > + uint32_t setup_size; > + uint32_t initrd_size; > + uint32_t kernel_size; > + uint32_t cmdline_size; > + uint32_t initrd_end_page, max_allowed_page; > + uint32_t segment_addr, stack_addr; > + > + bios_cfg_read_entry(&setup_addr, FW_CFG_SETUP_ADDR, 4); > + bios_cfg_read_entry(&setup_size, FW_CFG_SETUP_SIZE, 4); > + bios_cfg_read_entry(setup_addr, FW_CFG_SETUP_DATA, setup_size); > + > + set_es(setup_addr); > + > + /* For protocol < 0x203 we don't have initrd_max ... */ > + if (readw_es(0x206) < 0x203) { > + /* ... so we assume initrd_max = 0x37ffffff. */ > + writel_es(0x22c, 0x37ffffff); > + } > + > + bios_cfg_read_entry(&initrd_addr, FW_CFG_INITRD_ADDR, 4); > + bios_cfg_read_entry(&initrd_size, FW_CFG_INITRD_SIZE, 4); > + > + initrd_end_page = ((uint32_t)(initrd_addr + initrd_size) & -4096); > + max_allowed_page = (readl_es(0x22c) & -4096); > + > + if (initrd_end_page != 0 && max_allowed_page != 0 && > + initrd_end_page != max_allowed_page) { > + /* Initrd at the end of memory. Compute better initrd address > + * based on e801 data > + */ > + initrd_addr = (void *)((get_e801_addr() - initrd_size) & -4096); > + writel_es(0x218, (uint32_t)initrd_addr); > + > + } > + > + bios_cfg_read_entry(initrd_addr, FW_CFG_INITRD_DATA, initrd_size); > + > + bios_cfg_read_entry(&kernel_addr, FW_CFG_KERNEL_ADDR, 4); > + bios_cfg_read_entry(&kernel_size, FW_CFG_KERNEL_SIZE, 4); > + bios_cfg_read_entry(kernel_addr, FW_CFG_KERNEL_DATA, kernel_size); > + > + bios_cfg_read_entry(&cmdline_addr, FW_CFG_CMDLINE_ADDR, 4); > + bios_cfg_read_entry(&cmdline_size, FW_CFG_CMDLINE_SIZE, 4); > + bios_cfg_read_entry(cmdline_addr, FW_CFG_CMDLINE_DATA, cmdline_size); > + > + /* Boot linux */ > + segment_addr = ((uint32_t)setup_addr >> 4); > + stack_addr = (uint32_t)(cmdline_addr - setup_addr - 16); > + > + /* As we are changing critical registers, we cannot leave freedom to the > + * compiler. > + */ > + asm("movw %%ax, %%ds\n" > + "movw %%ax, %%es\n" > + "movw %%ax, %%fs\n" > + "movw %%ax, %%gs\n" > + "movw %%ax, %%ss\n" > + "movl %%ebx, %%esp\n" > + "addw $0x20, %%ax\n" > + "pushw %%ax\n" /* CS */ > + "pushw $0\n" /* IP */ > + /* Clear registers and jump to Linux */ > + "xor %%ebx, %%ebx\n" > + "xor %%ecx, %%ecx\n" > + "xor %%edx, %%edx\n" > + "xor %%edi, %%edi\n" > + "xor %%ebp, %%ebp\n" > + "lretw\n" > + : : "a"(segment_addr), "b"(stack_addr)); > +} >
On Mon, May 23, 2016 at 05:05:15PM +0200, Paolo Bonzini wrote: > > > On 11/05/2016 23:06, Richard W.M. Jones wrote: > > From: Marc Marí <markmb@redhat.com> > > > > This optionrom is based on linuxboot.S. > > > > Signed-off-by: Marc Marí <markmb@redhat.com> > > Signed-off-by: Richard W.M. Jones <rjones@redhat.com> > > Hmm, I hadn't noticed that you added -m16. That breaks on even > not-too-old GCC (such as 4.8 on RHEL/CentOS 7). Can you add some > Makefile logic to switch between "-m16" and a "-include code16gcc.h" > that only contains 'asm(".code16gcc");'? I'll note that we did know that -m16 would break on gcc < 4.9. See Stefan's message here: https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg01238.html However you're right we shouldn't break RHEL 7, so I'll try to implement your suggested fix in the next version. > Also, you need to add linuxboot_dma.bin after linuxboot.bin in the > main Makefile. Ah ha, I was wondering why I had to copy the file manually after building it ... Rich. > Thanks, > > Paolo > > > --- > > .gitignore | 4 + > > hw/i386/pc.c | 10 +- > > hw/nvram/fw_cfg.c | 2 +- > > include/hw/nvram/fw_cfg.h | 1 + > > pc-bios/optionrom/Makefile | 13 +- > > pc-bios/optionrom/linuxboot_dma.c | 291 ++++++++++++++++++++++++++++++++++++++ > > 6 files changed, 316 insertions(+), 5 deletions(-) > > create mode 100644 pc-bios/optionrom/linuxboot_dma.c > > > > diff --git a/.gitignore b/.gitignore > > index 88a80ff..101d1e0 100644 > > --- a/.gitignore > > +++ b/.gitignore > > @@ -94,6 +94,10 @@ > > /pc-bios/optionrom/linuxboot.bin > > /pc-bios/optionrom/linuxboot.raw > > /pc-bios/optionrom/linuxboot.img > > +/pc-bios/optionrom/linuxboot_dma.asm > > +/pc-bios/optionrom/linuxboot_dma.bin > > +/pc-bios/optionrom/linuxboot_dma.raw > > +/pc-bios/optionrom/linuxboot_dma.img > > /pc-bios/optionrom/multiboot.asm > > /pc-bios/optionrom/multiboot.bin > > /pc-bios/optionrom/multiboot.raw > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > > index 99437e0..098d571 100644 > > --- a/hw/i386/pc.c > > +++ b/hw/i386/pc.c > > @@ -999,8 +999,13 @@ static void load_linux(PCMachineState *pcms, > > fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_SIZE, setup_size); > > fw_cfg_add_bytes(fw_cfg, FW_CFG_SETUP_DATA, setup, setup_size); > > > > - option_rom[nb_option_roms].name = "linuxboot.bin"; > > - option_rom[nb_option_roms].bootindex = 0; > > + if (fw_cfg_dma_enabled(fw_cfg)) { > > + option_rom[nb_option_roms].name = "linuxboot_dma.bin"; > > + option_rom[nb_option_roms].bootindex = 0; > > + } else { > > + option_rom[nb_option_roms].name = "linuxboot.bin"; > > + option_rom[nb_option_roms].bootindex = 0; > > + } > > nb_option_roms++; > > } > > > > @@ -1263,6 +1268,7 @@ void xen_load_linux(PCMachineState *pcms) > > load_linux(pcms, fw_cfg); > > for (i = 0; i < nb_option_roms; i++) { > > assert(!strcmp(option_rom[i].name, "linuxboot.bin") || > > + !strcmp(option_rom[i].name, "linuxboot_dma.bin") || > > !strcmp(option_rom[i].name, "multiboot.bin")); > > rom_add_option(option_rom[i].name, option_rom[i].bootindex); > > } > > diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c > > index 999f480..114aea8 100644 > > --- a/hw/nvram/fw_cfg.c > > +++ b/hw/nvram/fw_cfg.c > > @@ -551,7 +551,7 @@ static bool is_version_1(void *opaque, int version_id) > > return version_id == 1; > > } > > > > -static bool fw_cfg_dma_enabled(void *opaque) > > +bool fw_cfg_dma_enabled(void *opaque) > > { > > FWCfgState *s = opaque; > > > > diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h > > index d008112..5c27a1f 100644 > > --- a/include/hw/nvram/fw_cfg.h > > +++ b/include/hw/nvram/fw_cfg.h > > @@ -182,5 +182,6 @@ FWCfgState *fw_cfg_init_mem_wide(hwaddr ctl_addr, > > hwaddr dma_addr, AddressSpace *dma_as); > > > > FWCfgState *fw_cfg_find(void); > > +bool fw_cfg_dma_enabled(void *opaque); > > > > #endif > > diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile > > index ce4852a..a51dd6e 100644 > > --- a/pc-bios/optionrom/Makefile > > +++ b/pc-bios/optionrom/Makefile > > @@ -13,15 +13,24 @@ CFLAGS := -Wall -Wstrict-prototypes -Werror -fomit-frame-pointer -fno-builtin > > CFLAGS += -I$(SRC_PATH) > > CFLAGS += $(call cc-option, $(CFLAGS), -fno-stack-protector) > > CFLAGS += $(CFLAGS_NOPIE) > > +CFLAGS += -m16 > > QEMU_CFLAGS = $(CFLAGS) > > > > -build-all: multiboot.bin linuxboot.bin kvmvapic.bin > > +ASFLAGS += -32 > > + > > +build-all: multiboot.bin linuxboot.bin linuxboot_dma.bin kvmvapic.bin > > > > # suppress auto-removal of intermediate files > > .SECONDARY: > > > > +ifdef CONFIG_WIN32 > > +LD_EMULATION = i386pe > > +else > > +LD_EMULATION = elf_i386 > > +endif > > + > > %.img: %.o > > - $(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -Ttext 0 -e _start -s -o $@ $<," Building $(TARGET_DIR)$@") > > + $(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -m $(LD_EMULATION) -Ttext 0 -e _start -s -o $@ $<," Building $(TARGET_DIR)$@") > > > > %.raw: %.img > > $(call quiet-command,$(OBJCOPY) -O binary -j .text $< $@," Building $(TARGET_DIR)$@") > > diff --git a/pc-bios/optionrom/linuxboot_dma.c b/pc-bios/optionrom/linuxboot_dma.c > > new file mode 100644 > > index 0000000..8ebc480 > > --- /dev/null > > +++ b/pc-bios/optionrom/linuxboot_dma.c > > @@ -0,0 +1,291 @@ > > +/* > > + * Linux Boot Option ROM for fw_cfg DMA > > + * > > + * This program is free software; you can redistribute it and/or modify > > + * it under the terms of the GNU General Public License as published by > > + * the Free Software Foundation; either version 2 of the License, or > > + * (at your option) any later version. > > + * > > + * This program is distributed in the hope that it will be useful, > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > + * GNU General Public License for more details. > > + * > > + * You should have received a copy of the GNU General Public License > > + * along with this program; if not, see <http://www.gnu.org/licenses/>. > > + * > > + * Copyright (c) 2015-2016 Red Hat Inc. > > + * Authors: > > + * Marc Marí <markmb@redhat.com> > > + * Richard W.M. Jones <rjones@redhat.com> > > + */ > > + > > +asm( > > +".text\n" > > +".global _start\n" > > +"_start:\n" > > +" .short 0xaa55\n" > > +" .byte 0\n" /* size in 512 units, filled in by signrom.py */ > > +" .byte 0xcb\n" /* far return without prefix */ > > +" .org 0x18\n" > > +" .short 0\n" > > +" .short _pnph\n" > > +"_pnph:\n" > > +" .ascii \"$PnP\"\n" > > +" .byte 0x01\n" > > +" .byte (_pnph_len / 16)\n" > > +" .short 0x0000\n" > > +" .byte 0x00\n" > > +" .byte 0x00\n" > > +" .long 0x00000000\n" > > +" .short _manufacturer\n" > > +" .short _product\n" > > +" .long 0x00000000\n" > > +" .short 0x0000\n" > > +" .short 0x0000\n" > > +" .short _bev\n" > > +" .short 0x0000\n" > > +" .short 0x0000\n" > > +" .equ _pnph_len, . - _pnph\n" > > +"_manufacturer:\n" > > +" .asciz \"QEMU\"\n" > > +"_product:\n" > > +" .asciz \"Linux loader DMA\"\n" > > +" .align 4, 0\n" > > +"_bev:\n" > > +" cli\n" > > +" cld\n" > > +" jmp load_kernel\n" > > +); > > + > > +#include "../../include/hw/nvram/fw_cfg_keys.h" > > + > > +/* QEMU_CFG_DMA_CONTROL bits */ > > +#define BIOS_CFG_DMA_CTL_ERROR 0x01 > > +#define BIOS_CFG_DMA_CTL_READ 0x02 > > +#define BIOS_CFG_DMA_CTL_SKIP 0x04 > > +#define BIOS_CFG_DMA_CTL_SELECT 0x08 > > + > > +#define BIOS_CFG_DMA_ADDR_HIGH 0x514 > > +#define BIOS_CFG_DMA_ADDR_LOW 0x518 > > + > > +#define uint64_t unsigned long long > > +#define uint32_t unsigned int > > +#define uint16_t unsigned short > > + > > +#define barrier() asm("" : : : "memory") > > + > > +typedef struct FWCfgDmaAccess { > > + uint32_t control; > > + uint32_t length; > > + uint64_t address; > > +} __attribute__((packed)) FWCfgDmaAccess; > > + > > +static inline void outl(uint32_t value, uint16_t port) > > +{ > > + asm("outl %0, %w1" : : "a"(value), "Nd"(port)); > > +} > > + > > +static inline void set_es(void *addr) > > +{ > > + uint32_t seg = (uint32_t)addr >> 4; > > + asm("movl %0, %%es" : : "r"(seg)); > > +} > > + > > +#ifdef __clang__ > > +#define ADDR32 > > +#else > > +#define ADDR32 "addr32 " > > +#endif > > + > > +static inline uint16_t readw_es(uint16_t offset) > > +{ > > + uint16_t val; > > + asm(ADDR32 "movw %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset)); > > + barrier(); > > + return val; > > +} > > + > > +static inline uint32_t readl_es(uint16_t offset) > > +{ > > + uint32_t val; > > + asm(ADDR32 "movl %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset)); > > + barrier(); > > + return val; > > +} > > + > > +static inline void writel_es(uint16_t offset, uint32_t val) > > +{ > > + barrier(); > > + asm(ADDR32 "movl %0, %%es:(%1)" : : "r"(val), "r"((uint32_t)offset)); > > +} > > + > > +static inline uint32_t bswap32(uint32_t x) > > +{ > > + return > > + ((x & 0x000000ffU) << 24) | > > + ((x & 0x0000ff00U) << 8) | > > + ((x & 0x00ff0000U) >> 8) | > > + ((x & 0xff000000U) >> 24); > > +} > > + > > +static inline uint64_t bswap64(uint64_t x) > > +{ > > + return > > + ((x & 0x00000000000000ffULL) << 56) | > > + ((x & 0x000000000000ff00ULL) << 40) | > > + ((x & 0x0000000000ff0000ULL) << 24) | > > + ((x & 0x00000000ff000000ULL) << 8) | > > + ((x & 0x000000ff00000000ULL) >> 8) | > > + ((x & 0x0000ff0000000000ULL) >> 24) | > > + ((x & 0x00ff000000000000ULL) >> 40) | > > + ((x & 0xff00000000000000ULL) >> 56); > > +} > > + > > +static inline uint64_t cpu_to_be64(uint64_t x) > > +{ > > + return bswap64(x); > > +} > > + > > +static inline uint32_t cpu_to_be32(uint32_t x) > > +{ > > + return bswap32(x); > > +} > > + > > +static inline uint32_t be32_to_cpu(uint32_t x) > > +{ > > + return bswap32(x); > > +} > > + > > +static void bios_cfg_read_entry(void *buf, uint16_t entry, uint32_t len) > > +{ > > + FWCfgDmaAccess access; > > + uint32_t control = (entry << 16) | BIOS_CFG_DMA_CTL_SELECT > > + | BIOS_CFG_DMA_CTL_READ; > > + > > + access.address = cpu_to_be64((uint64_t)(uint32_t)buf); > > + access.length = cpu_to_be32(len); > > + access.control = cpu_to_be32(control); > > + > > + barrier(); > > + > > + outl(cpu_to_be32((uint32_t)&access), BIOS_CFG_DMA_ADDR_LOW); > > + > > + while (be32_to_cpu(access.control) & ~BIOS_CFG_DMA_CTL_ERROR) { > > + barrier(); > > + } > > +} > > + > > +/* Return top of memory using BIOS function E801. */ > > +static uint32_t get_e801_addr(void) > > +{ > > + uint16_t ax, bx, cx, dx; > > + uint32_t ret; > > + > > + asm("int $0x15\n" > > + : "=a"(ax), "=b"(bx), "=c"(cx), "=d"(dx) > > + : "a"(0xe801), "b"(0), "c"(0), "d"(0)); > > + > > + /* Not SeaBIOS, but in theory a BIOS could return CX=DX=0 in which > > + * case we need to use the result from AX & BX instead. > > + */ > > + if (cx == 0 && dx == 0) { > > + cx = ax; > > + dx = bx; > > + } > > + > > + if (dx) { > > + /* DX = extended memory above 16M, in 64K units. > > + * Convert it to bytes and return. > > + */ > > + ret = ((uint32_t)dx + 256 /* 16M in 64K units */) << 16; > > + } else { > > + /* This is a fallback path for machines with <= 16MB of RAM, > > + * which probably would never be the case, but deal with it > > + * anyway. > > + * > > + * CX = extended memory between 1M and 16M, in kilobytes > > + * Convert it to bytes and return. > > + */ > > + ret = ((uint32_t)cx + 1024 /* 1M in K */) << 10; > > + } > > + > > + return ret; > > +} > > + > > +void load_kernel(void) > > +{ > > + void *setup_addr; > > + void *initrd_addr; > > + void *kernel_addr; > > + void *cmdline_addr; > > + uint32_t setup_size; > > + uint32_t initrd_size; > > + uint32_t kernel_size; > > + uint32_t cmdline_size; > > + uint32_t initrd_end_page, max_allowed_page; > > + uint32_t segment_addr, stack_addr; > > + > > + bios_cfg_read_entry(&setup_addr, FW_CFG_SETUP_ADDR, 4); > > + bios_cfg_read_entry(&setup_size, FW_CFG_SETUP_SIZE, 4); > > + bios_cfg_read_entry(setup_addr, FW_CFG_SETUP_DATA, setup_size); > > + > > + set_es(setup_addr); > > + > > + /* For protocol < 0x203 we don't have initrd_max ... */ > > + if (readw_es(0x206) < 0x203) { > > + /* ... so we assume initrd_max = 0x37ffffff. */ > > + writel_es(0x22c, 0x37ffffff); > > + } > > + > > + bios_cfg_read_entry(&initrd_addr, FW_CFG_INITRD_ADDR, 4); > > + bios_cfg_read_entry(&initrd_size, FW_CFG_INITRD_SIZE, 4); > > + > > + initrd_end_page = ((uint32_t)(initrd_addr + initrd_size) & -4096); > > + max_allowed_page = (readl_es(0x22c) & -4096); > > + > > + if (initrd_end_page != 0 && max_allowed_page != 0 && > > + initrd_end_page != max_allowed_page) { > > + /* Initrd at the end of memory. Compute better initrd address > > + * based on e801 data > > + */ > > + initrd_addr = (void *)((get_e801_addr() - initrd_size) & -4096); > > + writel_es(0x218, (uint32_t)initrd_addr); > > + > > + } > > + > > + bios_cfg_read_entry(initrd_addr, FW_CFG_INITRD_DATA, initrd_size); > > + > > + bios_cfg_read_entry(&kernel_addr, FW_CFG_KERNEL_ADDR, 4); > > + bios_cfg_read_entry(&kernel_size, FW_CFG_KERNEL_SIZE, 4); > > + bios_cfg_read_entry(kernel_addr, FW_CFG_KERNEL_DATA, kernel_size); > > + > > + bios_cfg_read_entry(&cmdline_addr, FW_CFG_CMDLINE_ADDR, 4); > > + bios_cfg_read_entry(&cmdline_size, FW_CFG_CMDLINE_SIZE, 4); > > + bios_cfg_read_entry(cmdline_addr, FW_CFG_CMDLINE_DATA, cmdline_size); > > + > > + /* Boot linux */ > > + segment_addr = ((uint32_t)setup_addr >> 4); > > + stack_addr = (uint32_t)(cmdline_addr - setup_addr - 16); > > + > > + /* As we are changing critical registers, we cannot leave freedom to the > > + * compiler. > > + */ > > + asm("movw %%ax, %%ds\n" > > + "movw %%ax, %%es\n" > > + "movw %%ax, %%fs\n" > > + "movw %%ax, %%gs\n" > > + "movw %%ax, %%ss\n" > > + "movl %%ebx, %%esp\n" > > + "addw $0x20, %%ax\n" > > + "pushw %%ax\n" /* CS */ > > + "pushw $0\n" /* IP */ > > + /* Clear registers and jump to Linux */ > > + "xor %%ebx, %%ebx\n" > > + "xor %%ecx, %%ecx\n" > > + "xor %%edx, %%edx\n" > > + "xor %%edi, %%edi\n" > > + "xor %%ebp, %%ebp\n" > > + "lretw\n" > > + : : "a"(segment_addr), "b"(stack_addr)); > > +} > >
diff --git a/.gitignore b/.gitignore index 88a80ff..101d1e0 100644 --- a/.gitignore +++ b/.gitignore @@ -94,6 +94,10 @@ /pc-bios/optionrom/linuxboot.bin /pc-bios/optionrom/linuxboot.raw /pc-bios/optionrom/linuxboot.img +/pc-bios/optionrom/linuxboot_dma.asm +/pc-bios/optionrom/linuxboot_dma.bin +/pc-bios/optionrom/linuxboot_dma.raw +/pc-bios/optionrom/linuxboot_dma.img /pc-bios/optionrom/multiboot.asm /pc-bios/optionrom/multiboot.bin /pc-bios/optionrom/multiboot.raw diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 99437e0..098d571 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -999,8 +999,13 @@ static void load_linux(PCMachineState *pcms, fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_SIZE, setup_size); fw_cfg_add_bytes(fw_cfg, FW_CFG_SETUP_DATA, setup, setup_size); - option_rom[nb_option_roms].name = "linuxboot.bin"; - option_rom[nb_option_roms].bootindex = 0; + if (fw_cfg_dma_enabled(fw_cfg)) { + option_rom[nb_option_roms].name = "linuxboot_dma.bin"; + option_rom[nb_option_roms].bootindex = 0; + } else { + option_rom[nb_option_roms].name = "linuxboot.bin"; + option_rom[nb_option_roms].bootindex = 0; + } nb_option_roms++; } @@ -1263,6 +1268,7 @@ void xen_load_linux(PCMachineState *pcms) load_linux(pcms, fw_cfg); for (i = 0; i < nb_option_roms; i++) { assert(!strcmp(option_rom[i].name, "linuxboot.bin") || + !strcmp(option_rom[i].name, "linuxboot_dma.bin") || !strcmp(option_rom[i].name, "multiboot.bin")); rom_add_option(option_rom[i].name, option_rom[i].bootindex); } diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c index 999f480..114aea8 100644 --- a/hw/nvram/fw_cfg.c +++ b/hw/nvram/fw_cfg.c @@ -551,7 +551,7 @@ static bool is_version_1(void *opaque, int version_id) return version_id == 1; } -static bool fw_cfg_dma_enabled(void *opaque) +bool fw_cfg_dma_enabled(void *opaque) { FWCfgState *s = opaque; diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h index d008112..5c27a1f 100644 --- a/include/hw/nvram/fw_cfg.h +++ b/include/hw/nvram/fw_cfg.h @@ -182,5 +182,6 @@ FWCfgState *fw_cfg_init_mem_wide(hwaddr ctl_addr, hwaddr dma_addr, AddressSpace *dma_as); FWCfgState *fw_cfg_find(void); +bool fw_cfg_dma_enabled(void *opaque); #endif diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile index ce4852a..a51dd6e 100644 --- a/pc-bios/optionrom/Makefile +++ b/pc-bios/optionrom/Makefile @@ -13,15 +13,24 @@ CFLAGS := -Wall -Wstrict-prototypes -Werror -fomit-frame-pointer -fno-builtin CFLAGS += -I$(SRC_PATH) CFLAGS += $(call cc-option, $(CFLAGS), -fno-stack-protector) CFLAGS += $(CFLAGS_NOPIE) +CFLAGS += -m16 QEMU_CFLAGS = $(CFLAGS) -build-all: multiboot.bin linuxboot.bin kvmvapic.bin +ASFLAGS += -32 + +build-all: multiboot.bin linuxboot.bin linuxboot_dma.bin kvmvapic.bin # suppress auto-removal of intermediate files .SECONDARY: +ifdef CONFIG_WIN32 +LD_EMULATION = i386pe +else +LD_EMULATION = elf_i386 +endif + %.img: %.o - $(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -Ttext 0 -e _start -s -o $@ $<," Building $(TARGET_DIR)$@") + $(call quiet-command,$(LD) $(LDFLAGS_NOPIE) -m $(LD_EMULATION) -Ttext 0 -e _start -s -o $@ $<," Building $(TARGET_DIR)$@") %.raw: %.img $(call quiet-command,$(OBJCOPY) -O binary -j .text $< $@," Building $(TARGET_DIR)$@") diff --git a/pc-bios/optionrom/linuxboot_dma.c b/pc-bios/optionrom/linuxboot_dma.c new file mode 100644 index 0000000..8ebc480 --- /dev/null +++ b/pc-bios/optionrom/linuxboot_dma.c @@ -0,0 +1,291 @@ +/* + * Linux Boot Option ROM for fw_cfg DMA + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see <http://www.gnu.org/licenses/>. + * + * Copyright (c) 2015-2016 Red Hat Inc. + * Authors: + * Marc Marí <markmb@redhat.com> + * Richard W.M. Jones <rjones@redhat.com> + */ + +asm( +".text\n" +".global _start\n" +"_start:\n" +" .short 0xaa55\n" +" .byte 0\n" /* size in 512 units, filled in by signrom.py */ +" .byte 0xcb\n" /* far return without prefix */ +" .org 0x18\n" +" .short 0\n" +" .short _pnph\n" +"_pnph:\n" +" .ascii \"$PnP\"\n" +" .byte 0x01\n" +" .byte (_pnph_len / 16)\n" +" .short 0x0000\n" +" .byte 0x00\n" +" .byte 0x00\n" +" .long 0x00000000\n" +" .short _manufacturer\n" +" .short _product\n" +" .long 0x00000000\n" +" .short 0x0000\n" +" .short 0x0000\n" +" .short _bev\n" +" .short 0x0000\n" +" .short 0x0000\n" +" .equ _pnph_len, . - _pnph\n" +"_manufacturer:\n" +" .asciz \"QEMU\"\n" +"_product:\n" +" .asciz \"Linux loader DMA\"\n" +" .align 4, 0\n" +"_bev:\n" +" cli\n" +" cld\n" +" jmp load_kernel\n" +); + +#include "../../include/hw/nvram/fw_cfg_keys.h" + +/* QEMU_CFG_DMA_CONTROL bits */ +#define BIOS_CFG_DMA_CTL_ERROR 0x01 +#define BIOS_CFG_DMA_CTL_READ 0x02 +#define BIOS_CFG_DMA_CTL_SKIP 0x04 +#define BIOS_CFG_DMA_CTL_SELECT 0x08 + +#define BIOS_CFG_DMA_ADDR_HIGH 0x514 +#define BIOS_CFG_DMA_ADDR_LOW 0x518 + +#define uint64_t unsigned long long +#define uint32_t unsigned int +#define uint16_t unsigned short + +#define barrier() asm("" : : : "memory") + +typedef struct FWCfgDmaAccess { + uint32_t control; + uint32_t length; + uint64_t address; +} __attribute__((packed)) FWCfgDmaAccess; + +static inline void outl(uint32_t value, uint16_t port) +{ + asm("outl %0, %w1" : : "a"(value), "Nd"(port)); +} + +static inline void set_es(void *addr) +{ + uint32_t seg = (uint32_t)addr >> 4; + asm("movl %0, %%es" : : "r"(seg)); +} + +#ifdef __clang__ +#define ADDR32 +#else +#define ADDR32 "addr32 " +#endif + +static inline uint16_t readw_es(uint16_t offset) +{ + uint16_t val; + asm(ADDR32 "movw %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset)); + barrier(); + return val; +} + +static inline uint32_t readl_es(uint16_t offset) +{ + uint32_t val; + asm(ADDR32 "movl %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset)); + barrier(); + return val; +} + +static inline void writel_es(uint16_t offset, uint32_t val) +{ + barrier(); + asm(ADDR32 "movl %0, %%es:(%1)" : : "r"(val), "r"((uint32_t)offset)); +} + +static inline uint32_t bswap32(uint32_t x) +{ + return + ((x & 0x000000ffU) << 24) | + ((x & 0x0000ff00U) << 8) | + ((x & 0x00ff0000U) >> 8) | + ((x & 0xff000000U) >> 24); +} + +static inline uint64_t bswap64(uint64_t x) +{ + return + ((x & 0x00000000000000ffULL) << 56) | + ((x & 0x000000000000ff00ULL) << 40) | + ((x & 0x0000000000ff0000ULL) << 24) | + ((x & 0x00000000ff000000ULL) << 8) | + ((x & 0x000000ff00000000ULL) >> 8) | + ((x & 0x0000ff0000000000ULL) >> 24) | + ((x & 0x00ff000000000000ULL) >> 40) | + ((x & 0xff00000000000000ULL) >> 56); +} + +static inline uint64_t cpu_to_be64(uint64_t x) +{ + return bswap64(x); +} + +static inline uint32_t cpu_to_be32(uint32_t x) +{ + return bswap32(x); +} + +static inline uint32_t be32_to_cpu(uint32_t x) +{ + return bswap32(x); +} + +static void bios_cfg_read_entry(void *buf, uint16_t entry, uint32_t len) +{ + FWCfgDmaAccess access; + uint32_t control = (entry << 16) | BIOS_CFG_DMA_CTL_SELECT + | BIOS_CFG_DMA_CTL_READ; + + access.address = cpu_to_be64((uint64_t)(uint32_t)buf); + access.length = cpu_to_be32(len); + access.control = cpu_to_be32(control); + + barrier(); + + outl(cpu_to_be32((uint32_t)&access), BIOS_CFG_DMA_ADDR_LOW); + + while (be32_to_cpu(access.control) & ~BIOS_CFG_DMA_CTL_ERROR) { + barrier(); + } +} + +/* Return top of memory using BIOS function E801. */ +static uint32_t get_e801_addr(void) +{ + uint16_t ax, bx, cx, dx; + uint32_t ret; + + asm("int $0x15\n" + : "=a"(ax), "=b"(bx), "=c"(cx), "=d"(dx) + : "a"(0xe801), "b"(0), "c"(0), "d"(0)); + + /* Not SeaBIOS, but in theory a BIOS could return CX=DX=0 in which + * case we need to use the result from AX & BX instead. + */ + if (cx == 0 && dx == 0) { + cx = ax; + dx = bx; + } + + if (dx) { + /* DX = extended memory above 16M, in 64K units. + * Convert it to bytes and return. + */ + ret = ((uint32_t)dx + 256 /* 16M in 64K units */) << 16; + } else { + /* This is a fallback path for machines with <= 16MB of RAM, + * which probably would never be the case, but deal with it + * anyway. + * + * CX = extended memory between 1M and 16M, in kilobytes + * Convert it to bytes and return. + */ + ret = ((uint32_t)cx + 1024 /* 1M in K */) << 10; + } + + return ret; +} + +void load_kernel(void) +{ + void *setup_addr; + void *initrd_addr; + void *kernel_addr; + void *cmdline_addr; + uint32_t setup_size; + uint32_t initrd_size; + uint32_t kernel_size; + uint32_t cmdline_size; + uint32_t initrd_end_page, max_allowed_page; + uint32_t segment_addr, stack_addr; + + bios_cfg_read_entry(&setup_addr, FW_CFG_SETUP_ADDR, 4); + bios_cfg_read_entry(&setup_size, FW_CFG_SETUP_SIZE, 4); + bios_cfg_read_entry(setup_addr, FW_CFG_SETUP_DATA, setup_size); + + set_es(setup_addr); + + /* For protocol < 0x203 we don't have initrd_max ... */ + if (readw_es(0x206) < 0x203) { + /* ... so we assume initrd_max = 0x37ffffff. */ + writel_es(0x22c, 0x37ffffff); + } + + bios_cfg_read_entry(&initrd_addr, FW_CFG_INITRD_ADDR, 4); + bios_cfg_read_entry(&initrd_size, FW_CFG_INITRD_SIZE, 4); + + initrd_end_page = ((uint32_t)(initrd_addr + initrd_size) & -4096); + max_allowed_page = (readl_es(0x22c) & -4096); + + if (initrd_end_page != 0 && max_allowed_page != 0 && + initrd_end_page != max_allowed_page) { + /* Initrd at the end of memory. Compute better initrd address + * based on e801 data + */ + initrd_addr = (void *)((get_e801_addr() - initrd_size) & -4096); + writel_es(0x218, (uint32_t)initrd_addr); + + } + + bios_cfg_read_entry(initrd_addr, FW_CFG_INITRD_DATA, initrd_size); + + bios_cfg_read_entry(&kernel_addr, FW_CFG_KERNEL_ADDR, 4); + bios_cfg_read_entry(&kernel_size, FW_CFG_KERNEL_SIZE, 4); + bios_cfg_read_entry(kernel_addr, FW_CFG_KERNEL_DATA, kernel_size); + + bios_cfg_read_entry(&cmdline_addr, FW_CFG_CMDLINE_ADDR, 4); + bios_cfg_read_entry(&cmdline_size, FW_CFG_CMDLINE_SIZE, 4); + bios_cfg_read_entry(cmdline_addr, FW_CFG_CMDLINE_DATA, cmdline_size); + + /* Boot linux */ + segment_addr = ((uint32_t)setup_addr >> 4); + stack_addr = (uint32_t)(cmdline_addr - setup_addr - 16); + + /* As we are changing critical registers, we cannot leave freedom to the + * compiler. + */ + asm("movw %%ax, %%ds\n" + "movw %%ax, %%es\n" + "movw %%ax, %%fs\n" + "movw %%ax, %%gs\n" + "movw %%ax, %%ss\n" + "movl %%ebx, %%esp\n" + "addw $0x20, %%ax\n" + "pushw %%ax\n" /* CS */ + "pushw $0\n" /* IP */ + /* Clear registers and jump to Linux */ + "xor %%ebx, %%ebx\n" + "xor %%ecx, %%ecx\n" + "xor %%edx, %%edx\n" + "xor %%edi, %%edi\n" + "xor %%ebp, %%ebp\n" + "lretw\n" + : : "a"(segment_addr), "b"(stack_addr)); +}