[PATCH v3 08/16] objtool: Add elf_create_reloc() helper

From: Peter Zijlstra
Date: Fri Mar 26 2021 - 11:14:41 EST

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We have 4 instances of adding a relocation. Create a common helper
to avoid growing even more.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
tools/objtool/check.c | 78 ++++++--------------------------
tools/objtool/elf.c | 86 +++++++++++++++++++++++-------------
tools/objtool/include/objtool/elf.h | 10 ++--
tools/objtool/orc_gen.c | 30 ++----------
4 files changed, 85 insertions(+), 119 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -433,8 +433,7 @@ static int add_dead_ends(struct objtool_

static int create_static_call_sections(struct objtool_file *file)
{
- struct section *sec, *reloc_sec;
- struct reloc *reloc;
+ struct section *sec;
struct static_call_site *site;
struct instruction *insn;
struct symbol *key_sym;
@@ -460,8 +459,7 @@ static int create_static_call_sections(s
if (!sec)
return -1;

- reloc_sec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
- if (!reloc_sec)
+ if (!elf_create_reloc_section(file->elf, sec, SHT_RELA))
return -1;

idx = 0;
@@ -471,25 +469,11 @@ static int create_static_call_sections(s
memset(site, 0, sizeof(struct static_call_site));

/* populate reloc for 'addr' */
- reloc = malloc(sizeof(*reloc));
-
- if (!reloc) {
- perror("malloc");
+ if (elf_add_reloc_to_insn(file->elf, sec,
+ idx * sizeof(struct static_call_site),
+ R_X86_64_PC32,
+ insn->sec, insn->offset))
return -1;
- }
- memset(reloc, 0, sizeof(*reloc));
-
- insn_to_reloc_sym_addend(insn->sec, insn->offset, reloc);
- if (!reloc->sym) {
- WARN_FUNC("static call tramp: missing containing symbol",
- insn->sec, insn->offset);
- return -1;
- }
-
- reloc->type = R_X86_64_PC32;
- reloc->offset = idx * sizeof(struct static_call_site);
- reloc->sec = reloc_sec;
- elf_add_reloc(file->elf, reloc);

/* find key symbol */
key_name = strdup(insn->call_dest->name);
@@ -526,18 +510,11 @@ static int create_static_call_sections(s
free(key_name);

/* populate reloc for 'key' */
- reloc = malloc(sizeof(*reloc));
- if (!reloc) {
- perror("malloc");
+ if (elf_add_reloc(file->elf, sec,
+ idx * sizeof(struct static_call_site) + 4,
+ R_X86_64_PC32, key_sym,
+ is_sibling_call(insn) * STATIC_CALL_SITE_TAIL))
return -1;
- }
- memset(reloc, 0, sizeof(*reloc));
- reloc->sym = key_sym;
- reloc->addend = is_sibling_call(insn) ? STATIC_CALL_SITE_TAIL : 0;
- reloc->type = R_X86_64_PC32;
- reloc->offset = idx * sizeof(struct static_call_site) + 4;
- reloc->sec = reloc_sec;
- elf_add_reloc(file->elf, reloc);

idx++;
}
@@ -547,8 +524,7 @@ static int create_static_call_sections(s

static int create_mcount_loc_sections(struct objtool_file *file)
{
- struct section *sec, *reloc_sec;
- struct reloc *reloc;
+ struct section *sec;
unsigned long *loc;
struct instruction *insn;
int idx;
@@ -571,8 +547,7 @@ static int create_mcount_loc_sections(st
if (!sec)
return -1;

- reloc_sec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
- if (!reloc_sec)
+ if (!elf_create_reloc_section(file->elf, sec, SHT_RELA))
return -1;

idx = 0;
@@ -581,32 +556,11 @@ static int create_mcount_loc_sections(st
loc = (unsigned long *)sec->data->d_buf + idx;
memset(loc, 0, sizeof(unsigned long));

- reloc = malloc(sizeof(*reloc));
- if (!reloc) {
- perror("malloc");
+ if (elf_add_reloc_to_insn(file->elf, sec,
+ idx * sizeof(unsigned long),
+ R_X86_64_64,
+ insn->sec, insn->offset))
return -1;
- }
- memset(reloc, 0, sizeof(*reloc));
-
- if (insn->sec->sym) {
- reloc->sym = insn->sec->sym;
- reloc->addend = insn->offset;
- } else {
- reloc->sym = find_symbol_containing(insn->sec, insn->offset);
-
- if (!reloc->sym) {
- WARN("missing symbol for insn at offset 0x%lx\n",
- insn->offset);
- return -1;
- }
-
- reloc->addend = insn->offset - reloc->sym->offset;
- }
-
- reloc->type = R_X86_64_64;
- reloc->offset = idx * sizeof(unsigned long);
- reloc->sec = reloc_sec;
- elf_add_reloc(file->elf, reloc);

idx++;
}
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -211,32 +211,6 @@ struct reloc *find_reloc_by_dest(const s
return find_reloc_by_dest_range(elf, sec, offset, 1);
}

-void insn_to_reloc_sym_addend(struct section *sec, unsigned long offset,
- struct reloc *reloc)
-{
- if (sec->sym) {
- reloc->sym = sec->sym;
- reloc->addend = offset;
- return;
- }
-
- /*
- * The Clang assembler strips section symbols, so we have to reference
- * the function symbol instead:
- */
- reloc->sym = find_symbol_containing(sec, offset);
- if (!reloc->sym) {
- /*
- * Hack alert. This happens when we need to reference the NOP
- * pad insn immediately after the function.
- */
- reloc->sym = find_symbol_containing(sec, offset - 1);
- }
-
- if (reloc->sym)
- reloc->addend = offset - reloc->sym->offset;
-}
-
static int read_sections(struct elf *elf)
{
Elf_Scn *s = NULL;
@@ -473,14 +447,66 @@ static int read_symbols(struct elf *elf)
return -1;
}

-void elf_add_reloc(struct elf *elf, struct reloc *reloc)
+int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
+ unsigned int type, struct symbol *sym, int addend)
{
- struct section *sec = reloc->sec;
+ struct reloc *reloc;

- list_add_tail(&reloc->list, &sec->reloc_list);
+ reloc = malloc(sizeof(*reloc));
+ if (!reloc) {
+ perror("malloc");
+ return -1;
+ }
+ memset(reloc, 0, sizeof(*reloc));
+
+ reloc->sec = sec->reloc;
+ reloc->offset = offset;
+ reloc->type = type;
+ reloc->sym = sym;
+ reloc->addend = addend;
+
+ list_add_tail(&reloc->list, &sec->reloc->reloc_list);
elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));

- sec->changed = true;
+ sec->reloc->changed = true;
+
+ return 0;
+}
+
+int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
+ unsigned long offset, unsigned int type,
+ struct section *insn_sec, unsigned long insn_off)
+{
+ struct symbol *sym;
+ int addend;
+
+ if (insn_sec->sym) {
+ sym = insn_sec->sym;
+ addend = insn_off;
+
+ } else {
+ /*
+ * The Clang assembler strips section symbols, so we have to
+ * reference the function symbol instead:
+ */
+ sym = find_symbol_containing(insn_sec, insn_off);
+ if (!sym) {
+ /*
+ * Hack alert. This happens when we need to reference
+ * the NOP pad insn immediately after the function.
+ */
+ sym = find_symbol_containing(insn_sec, insn_off - 1);
+ }
+
+ if (!sym) {
+ WARN("can't find symbol containing %s+0x%lx", insn_sec->name, insn_off);
+ return -1;
+ }
+
+ addend = insn_off - sym->offset;
+ }
+
+ return elf_add_reloc(elf, sec, offset, type, sym, addend);
}

static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -123,7 +123,13 @@ static inline u32 reloc_hash(struct relo
struct elf *elf_open_read(const char *name, int flags);
struct section *elf_create_section(struct elf *elf, const char *name, unsigned int sh_flags, size_t entsize, int nr);
struct section *elf_create_reloc_section(struct elf *elf, struct section *base, int reltype);
-void elf_add_reloc(struct elf *elf, struct reloc *reloc);
+
+int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
+ unsigned int type, struct symbol *sym, int addend);
+int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
+ unsigned long offset, unsigned int type,
+ struct section *insn_sec, unsigned long insn_off);
+
int elf_write_insn(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len,
const char *insn);
@@ -140,8 +146,6 @@ struct reloc *find_reloc_by_dest(const s
struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len);
struct symbol *find_func_containing(struct section *sec, unsigned long offset);
-void insn_to_reloc_sym_addend(struct section *sec, unsigned long offset,
- struct reloc *reloc);

#define for_each_sec(file, sec) \
list_for_each_entry(sec, &file->elf->sections, list)
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -82,12 +82,11 @@ static int init_orc_entry(struct orc_ent
}

static int write_orc_entry(struct elf *elf, struct section *orc_sec,
- struct section *ip_rsec, unsigned int idx,
+ struct section *ip_sec, unsigned int idx,
struct section *insn_sec, unsigned long insn_off,
struct orc_entry *o)
{
struct orc_entry *orc;
- struct reloc *reloc;

/* populate ORC data */
orc = (struct orc_entry *)orc_sec->data->d_buf + idx;
@@ -96,25 +95,9 @@ static int write_orc_entry(struct elf *e
orc->bp_offset = bswap_if_needed(orc->bp_offset);

/* populate reloc for ip */
- reloc = malloc(sizeof(*reloc));
- if (!reloc) {
- perror("malloc");
+ if (elf_add_reloc_to_insn(elf, ip_sec, idx * sizeof(int), R_X86_64_PC32,
+ insn_sec, insn_off))
return -1;
- }
- memset(reloc, 0, sizeof(*reloc));
-
- insn_to_reloc_sym_addend(insn_sec, insn_off, reloc);
- if (!reloc->sym) {
- WARN("missing symbol for insn at offset 0x%lx",
- insn_off);
- return -1;
- }
-
- reloc->type = R_X86_64_PC32;
- reloc->offset = idx * sizeof(int);
- reloc->sec = ip_rsec;
-
- elf_add_reloc(elf, reloc);

return 0;
}
@@ -153,7 +136,7 @@ static unsigned long alt_group_len(struc

int orc_create(struct objtool_file *file)
{
- struct section *sec, *ip_rsec, *orc_sec;
+ struct section *sec, *orc_sec;
unsigned int nr = 0, idx = 0;
struct orc_list_entry *entry;
struct list_head orc_list;
@@ -242,13 +225,12 @@ int orc_create(struct objtool_file *file
sec = elf_create_section(file->elf, ".orc_unwind_ip", 0, sizeof(int), nr);
if (!sec)
return -1;
- ip_rsec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
- if (!ip_rsec)
+ if (!elf_create_reloc_section(file->elf, sec, SHT_RELA))
return -1;

/* Write ORC entries to sections: */
list_for_each_entry(entry, &orc_list, list) {
- if (write_orc_entry(file->elf, orc_sec, ip_rsec, idx++,
+ if (write_orc_entry(file->elf, orc_sec, sec, idx++,
entry->insn_sec, entry->insn_off,
&entry->orc))
return -1;

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