[PATCH 13/17] x86/boot: Construct PE/COFF .text section from assembler

Ard Biesheuvel
2023-08-18T13:46:25Z

Now that the size of the setup block is fixed and visible to the
assembler, it is possible to populate the PE/COFF header fields from the
asm code directly, instead of poking the values into the binary using
the build tool. This will make it easier to reorganize the section
layout without having to tweak the build tool in lockstep.

Note that this change results in no differences in the resulting bzImage
binary.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/header.S | 22 +++------
arch/x86/boot/tools/build.c | 47 --------------------
2 files changed, 7 insertions(+), 62 deletions(-)

diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index f1fdffc9d2ca984b..c23c5feef37e55ed 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -79,14 +79,12 @@ optional_header:
.byte 0x02 # MajorLinkerVersion
.byte 0x14 # MinorLinkerVersion

- # Filled in by build.c
- .long 0 # SizeOfCode
+ .long setup_size + ZO__end - 0x200 # SizeOfCode

.long 0 # SizeOfInitializedData
.long 0 # SizeOfUninitializedData

- # Filled in by build.c
- .long 0x0000 # AddressOfEntryPoint
+ .long setup_size + ZO_efi_pe_entry # AddressOfEntryPoint

.long 0x0200 # BaseOfCode
#ifdef CONFIG_X86_32
@@ -109,10 +107,7 @@ extra_header_fields:
.word 0 # MinorSubsystemVersion
.long 0 # Win32VersionValue

- #
- # The size of the bzImage is written in tools/build.c
- #
- .long 0 # SizeOfImage
+ .long setup_size + ZO__end # SizeOfImage

.long 0x200 # SizeOfHeaders
.long 0 # CheckSum
@@ -203,18 +198,15 @@ section_table:
IMAGE_SCN_MEM_DISCARDABLE # Characteristics
#endif

- #
- # The offset & size fields are filled in by build.c.
- #
.ascii ".text"
.byte 0
.byte 0
.byte 0
- .long 0
- .long 0x0 # startup_{32,64}
- .long 0 # Size of initialized data
+ .long ZO__end
+ .long setup_size
+ .long ZO__edata # Size of initialized data
# on disk
- .long 0x0 # startup_{32,64}
+ .long setup_size
.long 0 # PointerToRelocations
.long 0 # PointerToLineNumbers
.word 0 # NumberOfRelocations
diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index 082c38a097713a2d..6b6282a96c6ab24d 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -53,10 +53,8 @@ u8 buf[(SETUP_SECT_NUM+1)*512];
#define PECOFF_COMPAT_RESERVE 0x0
#endif

-static unsigned long efi_pe_entry;
static unsigned long efi32_pe_entry;
static unsigned long _edata;
-static unsigned long _end;

/*----------------------------------------------------------------------*/

@@ -219,32 +217,6 @@ static void update_pecoff_setup_and_reloc(unsigned int size)
#endif
}

-static void update_pecoff_text(unsigned int text_start, unsigned int file_sz)
-{
- unsigned int pe_header;
- unsigned int text_sz = file_sz - text_start;
- unsigned int bss_sz = _end - text_sz;
-
- pe_header = get_unaligned_le32(&buf[0x3c]);
-
- /*
- * 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]);
-
- /* Size of image */
- put_unaligned_le32(file_sz + bss_sz, &buf[pe_header + 0x50]);
-
- /*
- * Address of entry point for PE/COFF executable
- */
- put_unaligned_le32(text_start + efi_pe_entry, &buf[pe_header + 0x28]);
-
- update_pecoff_section_header_fields(".text", text_start, text_sz + bss_sz,
- text_sz, text_start);
-}
-
static int reserve_pecoff_reloc_section(int c)
{
/* Reserve 0x20 bytes for .reloc section */
@@ -252,22 +224,9 @@ static int reserve_pecoff_reloc_section(int c)
return PECOFF_RELOC_RESERVE;
}

-static void efi_stub_defaults(void)
-{
- /* Defaults for old kernel */
-#ifdef CONFIG_X86_32
- efi_pe_entry = 0x10;
-#else
- efi_pe_entry = 0x210;
-#endif
-}
-
#else

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) {}
-static inline void efi_stub_defaults(void) {}

static inline int reserve_pecoff_reloc_section(int c)
{
@@ -310,10 +269,8 @@ static void parse_zoffset(char *fname)
p = (char *)buf;

while (p && *p) {
- PARSE_ZOFS(p, efi_pe_entry);
PARSE_ZOFS(p, efi32_pe_entry);
PARSE_ZOFS(p, _edata);
- PARSE_ZOFS(p, _end);

p = strchr(p, '\n');
while (p && (*p == '\r' || *p == '\n'))
@@ -331,8 +288,6 @@ int main(int argc, char ** argv)
void *kernel;
u32 crc = 0xffffffffUL;

- efi_stub_defaults();
-
if (argc != 5)
usage();
parse_zoffset(argv[3]);
@@ -380,8 +335,6 @@ int main(int argc, char ** argv)
kernel = mmap(NULL, sz, PROT_READ, MAP_SHARED, fd, 0);
if (kernel == MAP_FAILED)
die("Unable to mmap '%s': %m", argv[2]);
- update_pecoff_text(setup_sectors * 512, i + _edata);
-

crc = partial_crc32(buf, i, crc);
if (fwrite(buf, 1, i, dest) != i)
--
2.39.2