[PATCH v4 11/16] x86/boot/64: Remove inverse relocations

Brian Gerst
2024-03-22T16:53:01Z

Inverse relocations were needed to offset the effects of relocation for
RIP-relative accesses to zero-based percpu data. Now that the percpu
section is linked normally as part of the kernel image, they are no
longer needed.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
arch/x86/boot/compressed/misc.c | 14 +---
arch/x86/tools/relocs.c | 126 +-------------------------------
2 files changed, 2 insertions(+), 138 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index b70e4a21c15f..371288202268 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -235,7 +235,7 @@ static void handle_relocations(void *output, unsigned long output_len,

/*
* Process relocations: 32 bit relocations first then 64 bit after.
- * Three sets of binary relocations are added to the end of the kernel
+ * Two sets of binary relocations are added to the end of the kernel
* before compression. Each relocation table entry is the kernel
* address of the location which needs to be updated stored as a
* 32-bit value which is sign extended to 64 bits.
@@ -245,8 +245,6 @@ static void handle_relocations(void *output, unsigned long output_len,
* kernel bits...
* 0 - zero terminator for 64 bit relocations
* 64 bit relocation repeated
- * 0 - zero terminator for inverse 32 bit relocations
- * 32 bit inverse relocation repeated
* 0 - zero terminator for 32 bit relocations
* 32 bit relocation repeated
*
@@ -263,16 +261,6 @@ static void handle_relocations(void *output, unsigned long output_len,
*(uint32_t *)ptr += delta;
}
#ifdef CONFIG_X86_64
- while (*--reloc) {
- long extended = *reloc;
- extended += map;
-
- ptr = (unsigned long)extended;
- if (ptr < min_addr || ptr > max_addr)
- error("inverse 32-bit relocation outside of kernel!\n");
-
- *(int32_t *)ptr -= delta;
- }
for (reloc--; *reloc; reloc--) {
long extended = *reloc;
extended += map;
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 65e6f3d6d890..e490297a486b 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -28,7 +28,6 @@ struct relocs {
static struct relocs relocs16;
static struct relocs relocs32;
#if ELF_BITS == 64
-static struct relocs relocs32neg;
static struct relocs relocs64;
#define FMT PRIu64

@@ -89,7 +88,6 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = {
"__initramfs_start|"
"(jiffies|jiffies_64)|"
#if ELF_BITS == 64
- "__per_cpu_load|"
"init_per_cpu__.*|"
"__end_rodata_hpage_align|"
#endif
@@ -287,33 +285,6 @@ static const char *sym_name(const char *sym_strtab, Elf_Sym *sym)
return name;
}

-static Elf_Sym *sym_lookup(const char *symname)
-{
- int i;
- for (i = 0; i < shnum; i++) {
- struct section *sec = &secs[i];
- long nsyms;
- char *strtab;
- Elf_Sym *symtab;
- Elf_Sym *sym;
-
- if (sec->shdr.sh_type != SHT_SYMTAB)
- continue;
-
- nsyms = sec->shdr.sh_size/sizeof(Elf_Sym);
- symtab = sec->symtab;
- strtab = sec->link->strtab;
-
- for (sym = symtab; --nsyms >= 0; sym++) {
- if (!sym->st_name)
- continue;
- if (strcmp(symname, strtab + sym->st_name) == 0)
- return sym;
- }
- }
- return 0;
-}
-
#if BYTE_ORDER == LITTLE_ENDIAN
#define le16_to_cpu(val) (val)
#define le32_to_cpu(val) (val)
@@ -773,75 +744,8 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
}
}

-/*
- * The .data..percpu section is a special case for x86_64 SMP kernels.
- * It is used to initialize the actual per_cpu areas and to provide
- * definitions for the per_cpu variables that correspond to their offsets
- * within the percpu area. Since the values of all of the symbols need
- * to be offsets from the start of the per_cpu area the virtual address
- * (sh_addr) of .data..percpu is 0 in SMP kernels.
- *
- * This means that:
- *
- * Relocations that reference symbols in the per_cpu area do not
- * need further relocation (since the value is an offset relative
- * to the start of the per_cpu area that does not change).
- *
- * Relocations that apply to the per_cpu area need to have their
- * offset adjusted by by the value of __per_cpu_load to make them
- * point to the correct place in the loaded image (because the
- * virtual address of .data..percpu is 0).
- *
- * For non SMP kernels .data..percpu is linked as part of the normal
- * kernel data and does not require special treatment.
- *
- */
-static int per_cpu_shndx = -1;
-static Elf_Addr per_cpu_load_addr;
-
-static void percpu_init(void)
-{
- int i;
- for (i = 0; i < shnum; i++) {
- ElfW(Sym) *sym;
- if (strcmp(sec_name(i), ".data..percpu"))
- continue;
-
- if (secs[i].shdr.sh_addr != 0) /* non SMP kernel */
- return;
-
- sym = sym_lookup("__per_cpu_load");
- if (!sym)
- die("can't find __per_cpu_load\n");
-
- per_cpu_shndx = i;
- per_cpu_load_addr = sym->st_value;
- return;
- }
-}
-
#if ELF_BITS == 64

-/*
- * Check to see if a symbol lies in the .data..percpu section.
- *
- * The linker incorrectly associates some symbols with the
- * .data..percpu section so we also need to check the symbol
- * name to make sure that we classify the symbol correctly.
- *
- * The GNU linker incorrectly associates:
- * __init_begin
- * __per_cpu_load
- *
- * The "gold" linker incorrectly associates:
- * init_per_cpu__gdt_page
- */
-static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
-{
- return 0;
-}
-
-
static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
const char *symname)
{
@@ -852,12 +756,6 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
if (sym->st_shndx == SHN_UNDEF)
return 0;

- /*
- * Adjust the offset if this reloc applies to the percpu section.
- */
- if (sec->shdr.sh_info == per_cpu_shndx)
- offset += per_cpu_load_addr;
-
switch (r_type) {
case R_X86_64_NONE:
/* NONE can be ignored. */
@@ -867,33 +765,21 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
case R_X86_64_PLT32:
case R_X86_64_REX_GOTPCRELX:
/*
- * PC relative relocations don't need to be adjusted unless
- * referencing a percpu symbol.
+ * PC relative relocations don't need to be adjusted.
*
* NB: R_X86_64_PLT32 can be treated as R_X86_64_PC32.
*/
- if (is_percpu_sym(sym, symname))
- add_reloc(&relocs32neg, offset);
break;

case R_X86_64_PC64:
/*
* Only used by jump labels
*/
- if (is_percpu_sym(sym, symname))
- die("Invalid R_X86_64_PC64 relocation against per-CPU symbol %s\n",
- symname);
break;

case R_X86_64_32:
case R_X86_64_32S:
case R_X86_64_64:
- /*
- * References to the percpu area don't need to be adjusted.
- */
- if (is_percpu_sym(sym, symname))
- break;
-
if (shn_abs) {
/*
* Whitelisted absolute symbols do not require
@@ -1107,7 +993,6 @@ static void emit_relocs(int as_text, int use_real_mode)
/* Order the relocations for more efficient processing */
sort_relocs(&relocs32);
#if ELF_BITS == 64
- sort_relocs(&relocs32neg);
sort_relocs(&relocs64);
#else
sort_relocs(&relocs16);
@@ -1139,13 +1024,6 @@ static void emit_relocs(int as_text, int use_real_mode)
/* Now print each relocation */
for (i = 0; i < relocs64.count; i++)
write_reloc(relocs64.offset[i], stdout);
-
- /* Print a stop */
- write_reloc(0, stdout);
-
- /* Now print each inverse 32-bit relocation */
- for (i = 0; i < relocs32neg.count; i++)
- write_reloc(relocs32neg.offset[i], stdout);
#endif

/* Print a stop */
@@ -1196,8 +1074,6 @@ void process(FILE *fp, int use_real_mode, int as_text,
read_strtabs(fp);
read_symtabs(fp);
read_relocs(fp);
- if (ELF_BITS == 64)
- percpu_init();
if (show_absolute_syms) {
print_absolute_symbols();
return;
--
2.44.0