Message-ID: <CAMj1kXG_RTcU9T1FLQX3ZyqwP8xrjaXbyOZtZveL_JkoNaRWsw@mail.gmail.com>
Date:   Thu, 9 Mar 2023 16:57:54 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Evgeniy Baskov <baskov@...ras.ru>
Cc:     Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>,
        "Limonciello, Mario" <mario.limonciello@....com>,
        joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 19/26] x86/build: Cleanup tools/build.c

On Thu, 15 Dec 2022 at 13:42, Evgeniy Baskov <baskov@...ras.ru> wrote:
>
> Use newer C standard. Since kernel requires C99 compiler now,
> we can make use of the new features to make the core more readable.
>
> Use mmap() for reading files also to make things simpler.
>
> Replace most magic numbers with defines.
>
> Should have no functional changes. This is done in preparation for the
> next changes that makes generated PE header more spec compliant.
>
> Tested-by: Mario Limonciello <mario.limonciello@....com>
> Tested-by: Peter Jones <pjones@...hat.com>
> Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
> ---
>  arch/x86/boot/tools/build.c | 387 +++++++++++++++++++++++-------------
>  1 file changed, 245 insertions(+), 142 deletions(-)
>
> diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
> index bd247692b701..fbc5315af032 100644
> --- a/arch/x86/boot/tools/build.c
> +++ b/arch/x86/boot/tools/build.c
> @@ -25,20 +25,21 @@
>   * Substantially overhauled by H. Peter Anvin, April 2007
>   */
>
> +#include <fcntl.h>
> +#include <stdarg.h>
> +#include <stdint.h>
>  #include <stdio.h>
> -#include <string.h>
>  #include <stdlib.h>
> -#include <stdarg.h>
> -#include <sys/types.h>
> +#include <string.h>
> +#include <sys/mman.h>
>  #include <sys/stat.h>
> +#include <sys/types.h>
>  #include <unistd.h>
> -#include <fcntl.h>
> -#include <sys/mman.h>
> +
>  #include <tools/le_byteshift.h>
> +#include <linux/pe.h>
>
> -typedef unsigned char  u8;
> -typedef unsigned short u16;
> -typedef unsigned int   u32;
> +#define round_up(x, n) (((x) + (n) - 1) & ~((n) - 1))
>
>  #define DEFAULT_MAJOR_ROOT 0
>  #define DEFAULT_MINOR_ROOT 0
> @@ -48,8 +49,13 @@ typedef unsigned int   u32;
>  #define SETUP_SECT_MIN 5
>  #define SETUP_SECT_MAX 64
>
> +#define PARAGRAPH_SIZE 16
> +#define SECTOR_SIZE 512
> +#define FILE_ALIGNMENT 512
> +#define SECTION_ALIGNMENT 4096
> +
>  /* This must be large enough to hold the entire setup */
> -u8 buf[SETUP_SECT_MAX*512];
> +uint8_t buf[SETUP_SECT_MAX*SECTOR_SIZE];
>
>  #define PECOFF_RELOC_RESERVE 0x20
>
> @@ -59,6 +65,52 @@ u8 buf[SETUP_SECT_MAX*512];
>  #define PECOFF_COMPAT_RESERVE 0x0
>  #endif
>
> +#define RELOC_SECTION_SIZE 10
> +
> +/* PE header has different format depending on the architecture */
> +#ifdef CONFIG_X86_64
> +typedef struct pe32plus_opt_hdr pe_opt_hdr;
> +#else
> +typedef struct pe32_opt_hdr pe_opt_hdr;
> +#endif
> +
> +static inline struct pe_hdr *get_pe_header(uint8_t *buf)
> +{
> +       uint32_t pe_offset = get_unaligned_le32(buf+MZ_HEADER_PEADDR_OFFSET);
> +       return (struct pe_hdr *)(buf + pe_offset);
> +}
> +
> +static inline pe_opt_hdr *get_pe_opt_header(uint8_t *buf)
> +{
> +       return (pe_opt_hdr *)(get_pe_header(buf) + 1);
> +}
> +
> +static inline struct section_header *get_sections(uint8_t *buf)
> +{
> +       pe_opt_hdr *hdr = get_pe_opt_header(buf);
> +       uint32_t n_data_dirs = get_unaligned_le32(&hdr->data_dirs);
> +       uint8_t *sections = (uint8_t *)(hdr + 1) + n_data_dirs*sizeof(struct data_dirent);
> +       return  (struct section_header *)sections;
> +}
> +
> +static inline struct data_directory *get_data_dirs(uint8_t *buf)
> +{
> +       pe_opt_hdr *hdr = get_pe_opt_header(buf);
> +       return (struct data_directory *)(hdr + 1);
> +}
> +
> +#ifdef CONFIG_EFI_DXE_MEM_ATTRIBUTES

Can we drop this conditional?
> +#define SCN_RW (IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_ALIGN_4096BYTES)
> +#define SCN_RX (IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_ALIGN_4096BYTES)
> +#define SCN_RO (IMAGE_SCN_MEM_READ | IMAGE_SCN_ALIGN_4096BYTES)

Please drop the alignment flags - they don't apply to executable only
object files.

> +#else
> +/* With memory protection disabled all sections are RWX */
> +#define SCN_RW (IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | \
> +               IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_ALIGN_4096BYTES)
> +#define SCN_RX SCN_RW
> +#define SCN_RO SCN_RW
> +#endif
> +
>  static unsigned long efi32_stub_entry;
>  static unsigned long efi64_stub_entry;
>  static unsigned long efi_pe_entry;
> @@ -70,7 +122,7 @@ static unsigned long _end;
>
>  /*----------------------------------------------------------------------*/
>
> -static const u32 crctab32[] = {
> +static const uint32_t crctab32[] = {

Replacing all the type names makes this patch very messy. Can we back
that out please?

>         0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
>         0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
>         0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
> @@ -125,12 +177,12 @@ static const u32 crctab32[] = {
>         0x2d02ef8d
>  };
>
> -static u32 partial_crc32_one(u8 c, u32 crc)
> +static uint32_t partial_crc32_one(uint8_t c, uint32_t crc)
>  {
>         return crctab32[(crc ^ c) & 0xff] ^ (crc >> 8);
>  }
>
> -static u32 partial_crc32(const u8 *s, int len, u32 crc)
> +static uint32_t partial_crc32(const uint8_t *s, int len, uint32_t crc)
>  {
>         while (len--)
>                 crc = partial_crc32_one(*s++, crc);
> @@ -152,57 +204,106 @@ static void usage(void)
>         die("Usage: build setup system zoffset.h image");
>  }
>
> +static void *map_file(const char *path, size_t *psize)
> +{
> +       struct stat statbuf;
> +       size_t size;
> +       void *addr;
> +       int fd;
> +
> +       fd = open(path, O_RDONLY);
> +       if (fd < 0)
> +               die("Unable to open `%s': %m", path);
> +       if (fstat(fd, &statbuf))
> +               die("Unable to stat `%s': %m", path);
> +
> +       size = statbuf.st_size;
> +       /*
> +        * Map one byte more, to allow adding null-terminator
> +        * for text files.
> +        */
> +       addr = mmap(NULL, size + 1, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
> +       if (addr == MAP_FAILED)
> +               die("Unable to mmap '%s': %m", path);
> +
> +       close(fd);
> +
> +       *psize = size;
> +       return addr;
> +}
> +
> +static void unmap_file(void *addr, size_t size)
> +{
> +       munmap(addr, size + 1);
> +}
> +
> +static void *map_output_file(const char *path, size_t size)
> +{
> +       void *addr;
> +       int fd;
> +
> +       fd = open(path, O_RDWR | O_CREAT, 0660);
> +       if (fd < 0)
> +               die("Unable to create `%s': %m", path);
> +
> +       if (ftruncate(fd, size))
> +               die("Unable to resize `%s': %m", path);
> +
> +       addr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> +       if (addr == MAP_FAILED)
> +               die("Unable to mmap '%s': %m", path);
> +
> +       return addr;
> +}
> +
>  #ifdef CONFIG_EFI_STUB
>
> -static void update_pecoff_section_header_fields(char *section_name, u32 vma, u32 size, u32 datasz, u32 offset)
> +static void update_pecoff_section_header_fields(char *section_name, uint32_t vma,
> +                                               uint32_t size, uint32_t datasz,
> +                                               uint32_t offset)
>  {
>         unsigned int pe_header;
>         unsigned short num_sections;
> -       u8 *section;
> +       struct section_header *section;
>
> -       pe_header = get_unaligned_le32(&buf[0x3c]);
> -       num_sections = get_unaligned_le16(&buf[pe_header + 6]);
> -
> -#ifdef CONFIG_X86_32
> -       section = &buf[pe_header + 0xa8];
> -#else
> -       section = &buf[pe_header + 0xb8];
> -#endif
> +       struct pe_hdr *hdr = get_pe_header(buf);
> +       num_sections = get_unaligned_le16(&hdr->sections);
> +       section = get_sections(buf);
>
>         while (num_sections > 0) {
> -               if (strncmp((char*)section, section_name, 8) == 0) {
> +               if (strncmp(section->name, section_name, 8) == 0) {
>                         /* section header size field */
> -                       put_unaligned_le32(size, section + 0x8);
> +                       put_unaligned_le32(size, &section->virtual_size);
>
>                         /* section header vma field */
> -                       put_unaligned_le32(vma, section + 0xc);
> +                       put_unaligned_le32(vma, &section->virtual_address);
>
>                         /* section header 'size of initialised data' field */
> -                       put_unaligned_le32(datasz, section + 0x10);
> +                       put_unaligned_le32(datasz, &section->raw_data_size);
>
>                         /* section header 'file offset' field */
> -                       put_unaligned_le32(offset, section + 0x14);
> +                       put_unaligned_le32(offset, &section->data_addr);
>
>                         break;
>                 }
> -               section += 0x28;
> +               section++;
>                 num_sections--;
>         }
>  }
>
> -static void update_pecoff_section_header(char *section_name, u32 offset, u32 size)
> +static void update_pecoff_section_header(char *section_name, uint32_t offset, uint32_t size)
>  {
>         update_pecoff_section_header_fields(section_name, offset, size, size, offset);
>  }
>
>  static void update_pecoff_setup_and_reloc(unsigned int size)
>  {
> -       u32 setup_offset = 0x200;
> -       u32 reloc_offset = size - PECOFF_RELOC_RESERVE - PECOFF_COMPAT_RESERVE;
> +       uint32_t setup_offset = SECTOR_SIZE;
> +       uint32_t reloc_offset = size - PECOFF_RELOC_RESERVE - PECOFF_COMPAT_RESERVE;
>  #ifdef CONFIG_EFI_MIXED
> -       u32 compat_offset = reloc_offset + PECOFF_RELOC_RESERVE;
> +       uint32_t compat_offset = reloc_offset + PECOFF_RELOC_RESERVE;
>  #endif
> -       u32 setup_size = reloc_offset - setup_offset;
> +       uint32_t setup_size = reloc_offset - setup_offset;
>
>         update_pecoff_section_header(".setup", setup_offset, setup_size);
>         update_pecoff_section_header(".reloc", reloc_offset, PECOFF_RELOC_RESERVE);
> @@ -211,8 +312,8 @@ static void update_pecoff_setup_and_reloc(unsigned int size)
>          * Modify .reloc section contents with a single entry. The
>          * relocation is applied to offset 10 of the relocation section.
>          */
> -       put_unaligned_le32(reloc_offset + 10, &buf[reloc_offset]);
> -       put_unaligned_le32(10, &buf[reloc_offset + 4]);
> +       put_unaligned_le32(reloc_offset + RELOC_SECTION_SIZE, &buf[reloc_offset]);
> +       put_unaligned_le32(RELOC_SECTION_SIZE, &buf[reloc_offset + 4]);
>
>  #ifdef CONFIG_EFI_MIXED
>         update_pecoff_section_header(".compat", compat_offset, PECOFF_COMPAT_RESERVE);
> @@ -224,19 +325,17 @@ static void update_pecoff_setup_and_reloc(unsigned int size)
>          */
>         buf[compat_offset] = 0x1;
>         buf[compat_offset + 1] = 0x8;
> -       put_unaligned_le16(0x14c, &buf[compat_offset + 2]);
> +       put_unaligned_le16(IMAGE_FILE_MACHINE_I386, &buf[compat_offset + 2]);
>         put_unaligned_le32(efi32_pe_entry + size, &buf[compat_offset + 4]);
>  #endif
>  }
>
> -static void update_pecoff_text(unsigned int text_start, unsigned int file_sz,
> +static unsigned int update_pecoff_sections(unsigned int text_start, unsigned int text_sz,
>                                unsigned int init_sz)
>  {
> -       unsigned int pe_header;
> -       unsigned int text_sz = file_sz - text_start;
> +       unsigned int file_sz = text_start + text_sz;
>         unsigned int bss_sz = init_sz - file_sz;
> -
> -       pe_header = get_unaligned_le32(&buf[0x3c]);
> +       pe_opt_hdr *hdr = get_pe_opt_header(buf);
>
>         /*
>          * The PE/COFF loader may load the image at an address which is
> @@ -254,18 +353,20 @@ static void update_pecoff_text(unsigned int text_start, unsigned int file_sz,
>          * Size of code: Subtract the size of the first sector (512 bytes)
>          * which includes the header.
>          */
> -       put_unaligned_le32(file_sz - 512 + bss_sz, &buf[pe_header + 0x1c]);
> +       put_unaligned_le32(file_sz - SECTOR_SIZE + bss_sz, &hdr->text_size);
>
>         /* Size of image */
> -       put_unaligned_le32(init_sz, &buf[pe_header + 0x50]);
> +       put_unaligned_le32(init_sz, &hdr->image_size);
>
>         /*
>          * Address of entry point for PE/COFF executable
>          */
> -       put_unaligned_le32(text_start + efi_pe_entry, &buf[pe_header + 0x28]);
> +       put_unaligned_le32(text_start + efi_pe_entry, &hdr->entry_point);
>
>         update_pecoff_section_header_fields(".text", text_start, text_sz + bss_sz,
>                                             text_sz, text_start);
> +
> +       return text_start + file_sz;
>  }
>
>  static int reserve_pecoff_reloc_section(int c)
> @@ -275,7 +376,7 @@ static int reserve_pecoff_reloc_section(int c)
>         return PECOFF_RELOC_RESERVE;
>  }
>
> -static void efi_stub_defaults(void)
> +static void efi_stub_update_defaults(void)
>  {
>         /* Defaults for old kernel */
>  #ifdef CONFIG_X86_32
> @@ -298,7 +399,7 @@ static void efi_stub_entry_update(void)
>
>  #ifdef CONFIG_EFI_MIXED
>         if (efi32_stub_entry != addr)
> -               die("32-bit and 64-bit EFI entry points do not match\n");
> +               die("32-bit and 64-bit EFI entry points do not match");
>  #endif
>  #endif
>         put_unaligned_le32(addr, &buf[0x264]);
> @@ -310,7 +411,7 @@ static inline void update_pecoff_setup_and_reloc(unsigned int size) {}
>  static inline void update_pecoff_text(unsigned int text_start,
>                                       unsigned int file_sz,
>                                       unsigned int init_sz) {}
> -static inline void efi_stub_defaults(void) {}
> +static inline void efi_stub_update_defaults(void) {}
>  static inline void efi_stub_entry_update(void) {}
>
>  static inline int reserve_pecoff_reloc_section(int c)
> @@ -338,20 +439,15 @@ static int reserve_pecoff_compat_section(int c)
>
>  static void parse_zoffset(char *fname)
>  {
> -       FILE *file;
> -       char *p;
> -       int c;
> +       size_t size;
> +       char *data, *p;
>
> -       file = fopen(fname, "r");
> -       if (!file)
> -               die("Unable to open `%s': %m", fname);
> -       c = fread(buf, 1, sizeof(buf) - 1, file);
> -       if (ferror(file))
> -               die("read-error on `zoffset.h'");
> -       fclose(file);
> -       buf[c] = 0;
> +       data = map_file(fname, &size);
>
> -       p = (char *)buf;
> +       /* We can do that, since we mapped one byte more */
> +       data[size] = 0;
> +
> +       p = (char *)data;
>
>         while (p && *p) {
>                 PARSE_ZOFS(p, efi32_stub_entry);
> @@ -367,82 +463,99 @@ static void parse_zoffset(char *fname)
>                 while (p && (*p == '\r' || *p == '\n'))
>                         p++;
>         }
> +
> +       unmap_file(data, size);
>  }
>
> -int main(int argc, char ** argv)
> +static unsigned int read_setup(char *path)
>  {
> -       unsigned int i, sz, setup_sectors, init_sz;
> -       int c;
> -       u32 sys_size;
> -       struct stat sb;
> -       FILE *file, *dest;
> -       int fd;
> -       void *kernel;
> -       u32 crc = 0xffffffffUL;
> -
> -       efi_stub_defaults();
> -
> -       if (argc != 5)
> -               usage();
> -       parse_zoffset(argv[3]);
> -
> -       dest = fopen(argv[4], "w");
> -       if (!dest)
> -               die("Unable to write `%s': %m", argv[4]);
> +       FILE *file;
> +       unsigned int setup_size, file_size;
>
>         /* Copy the setup code */
> -       file = fopen(argv[1], "r");
> +       file = fopen(path, "r");
>         if (!file)
> -               die("Unable to open `%s': %m", argv[1]);
> -       c = fread(buf, 1, sizeof(buf), file);
> +               die("Unable to open `%s': %m", path);
> +
> +       file_size = fread(buf, 1, sizeof(buf), file);
>         if (ferror(file))
>                 die("read-error on `setup'");
> -       if (c < 1024)
> +
> +       if (file_size < 2 * SECTOR_SIZE)
>                 die("The setup must be at least 1024 bytes");
> -       if (get_unaligned_le16(&buf[510]) != 0xAA55)
> +
> +       if (get_unaligned_le16(&buf[SECTOR_SIZE - 2]) != 0xAA55)
>                 die("Boot block hasn't got boot flag (0xAA55)");
> +
>         fclose(file);
>
> -       c += reserve_pecoff_compat_section(c);
> -       c += reserve_pecoff_reloc_section(c);
> +       /* Reserve space for PE sections */
> +       file_size += reserve_pecoff_compat_section(file_size);
> +       file_size += reserve_pecoff_reloc_section(file_size);
>
>         /* Pad unused space with zeros */
> -       setup_sectors = (c + 511) / 512;
> -       if (setup_sectors < SETUP_SECT_MIN)
> -               setup_sectors = SETUP_SECT_MIN;
> -       i = setup_sectors*512;
> -       memset(buf+c, 0, i-c);
>
> -       update_pecoff_setup_and_reloc(i);
> +       setup_size = round_up(file_size, SECTOR_SIZE);
> +
> +       if (setup_size < SETUP_SECT_MIN * SECTOR_SIZE)
> +               setup_size = SETUP_SECT_MIN * SECTOR_SIZE;
> +
> +       /*
> +        * Global buffer is already initialised
> +        * to 0, but just in case, zero out padding.
> +        */
> +
> +       memset(buf + file_size, 0, setup_size - file_size);
> +
> +       return setup_size;
> +}
> +
> +int main(int argc, char **argv)
> +{
> +       size_t kern_file_size;
> +       unsigned int setup_size;
> +       unsigned int setup_sectors;
> +       unsigned int init_size;
> +       unsigned int total_size;
> +       unsigned int kern_size;
> +       void *kernel;
> +       uint32_t crc = 0xffffffffUL;
> +       uint8_t *output;
> +
> +       if (argc != 5)
> +               usage();
> +
> +       efi_stub_update_defaults();
> +       parse_zoffset(argv[3]);
> +
> +       setup_size = read_setup(argv[1]);
> +
> +       setup_sectors = setup_size/SECTOR_SIZE;
>
>         /* Set the default root device */
>         put_unaligned_le16(DEFAULT_ROOT_DEV, &buf[508]);
>
> -       /* Open and stat the kernel file */
> -       fd = open(argv[2], O_RDONLY);
> -       if (fd < 0)
> -               die("Unable to open `%s': %m", argv[2]);
> -       if (fstat(fd, &sb))
> -               die("Unable to stat `%s': %m", argv[2]);
> -       sz = sb.st_size;
> -       kernel = mmap(NULL, sz, PROT_READ, MAP_SHARED, fd, 0);
> -       if (kernel == MAP_FAILED)
> -               die("Unable to mmap '%s': %m", argv[2]);
> -       /* Number of 16-byte paragraphs, including space for a 4-byte CRC */
> -       sys_size = (sz + 15 + 4) / 16;
> +       /* Map kernel file to memory */
> +       kernel = map_file(argv[2], &kern_file_size);
> +
>  #ifdef CONFIG_EFI_STUB
> -       /*
> -        * COFF requires minimum 32-byte alignment of sections, and
> -        * adding a signature is problematic without that alignment.
> -        */
> -       sys_size = (sys_size + 1) & ~1;
> +       /* PE specification require 512-byte minimum section file alignment */
> +       kern_size = round_up(kern_file_size + 4, SECTOR_SIZE);
> +       update_pecoff_setup_and_reloc(setup_size);
> +#else
> +       /* Number of 16-byte paragraphs, including space for a 4-byte CRC */
> +       kern_size = round_up(kern_file_size + 4, PARAGRAPH_SIZE);
>  #endif
>
>         /* Patch the setup code with the appropriate size parameters */
> -       buf[0x1f1] = setup_sectors-1;
> -       put_unaligned_le32(sys_size, &buf[0x1f4]);
> +       buf[0x1f1] = setup_sectors - 1;
> +       put_unaligned_le32(kern_size/PARAGRAPH_SIZE, &buf[0x1f4]);
> +
> +       /* Update kernel_info offset. */
> +       put_unaligned_le32(kernel_info, &buf[0x268]);
> +
> +       init_size = get_unaligned_le32(&buf[0x260]);
>
> -       init_sz = get_unaligned_le32(&buf[0x260]);
>  #ifdef CONFIG_EFI_STUB
>         /*
>          * The decompression buffer will start at ImageBase. When relocating
> @@ -458,45 +571,35 @@ int main(int argc, char ** argv)
>          * For future-proofing, increase init_sz if necessary.
>          */
>
> -       if (init_sz - _end < i + _ehead) {
> -               init_sz = (i + _ehead + _end + 4095) & ~4095;
> -               put_unaligned_le32(init_sz, &buf[0x260]);
> +       if (init_size - _end < setup_size + _ehead) {
> +               init_size = round_up(setup_size + _ehead + _end, SECTION_ALIGNMENT);
> +               put_unaligned_le32(init_size, &buf[0x260]);
>         }
> -#endif
> -       update_pecoff_text(setup_sectors * 512, i + (sys_size * 16), init_sz);
>
> -       efi_stub_entry_update();
> -
> -       /* Update kernel_info offset. */
> -       put_unaligned_le32(kernel_info, &buf[0x268]);
> +       total_size = update_pecoff_sections(setup_size, kern_size, init_size);
>
> -       crc = partial_crc32(buf, i, crc);
> -       if (fwrite(buf, 1, i, dest) != i)
> -               die("Writing setup failed");
> +       efi_stub_entry_update();
> +#else
> +       (void)init_size;
> +       total_size = setup_size + kern_size;
> +#endif
>
> -       /* Copy the kernel code */
> -       crc = partial_crc32(kernel, sz, crc);
> -       if (fwrite(kernel, 1, sz, dest) != sz)
> -               die("Writing kernel failed");
> +       output = map_output_file(argv[4], total_size);
>
> -       /* Add padding leaving 4 bytes for the checksum */
> -       while (sz++ < (sys_size*16) - 4) {
> -               crc = partial_crc32_one('\0', crc);
> -               if (fwrite("\0", 1, 1, dest) != 1)
> -                       die("Writing padding failed");
> -       }
> +       memcpy(output, buf, setup_size);
> +       memcpy(output + setup_size, kernel, kern_file_size);
> +       memset(output + setup_size + kern_file_size, 0, kern_size - kern_file_size);
>
> -       /* Write the CRC */
> -       put_unaligned_le32(crc, buf);
> -       if (fwrite(buf, 1, 4, dest) != 4)
> -               die("Writing CRC failed");
> +       /* Calculate and write kernel checksum. */
> +       crc = partial_crc32(output, total_size - 4, crc);
> +       put_unaligned_le32(crc, &output[total_size - 4]);
>
> -       /* Catch any delayed write failures */
> -       if (fclose(dest))
> -               die("Writing image failed");
> +       /* Catch any delayed write failures. */
> +       if (munmap(output, total_size) < 0)
> +               die("Writing kernel failed");
>
> -       close(fd);
> +       unmap_file(kernel, kern_file_size);
>
> -       /* Everything is OK */
> +       /* Everything is OK. */
>         return 0;
>  }
> --
> 2.37.4
>

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