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Message-ID: <86761fd1402f1187d23c655edee766cd2c96c5e7.1758067943.git.jpoimboe@kernel.org>
Date: Wed, 17 Sep 2025 09:04:02 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
Petr Mladek <pmladek@...e.com>,
Miroslav Benes <mbenes@...e.cz>,
Joe Lawrence <joe.lawrence@...hat.com>,
live-patching@...r.kernel.org,
Song Liu <song@...nel.org>,
laokz <laokz@...mail.com>,
Jiri Kosina <jikos@...nel.org>,
Marcos Paulo de Souza <mpdesouza@...e.com>,
Weinan Liu <wnliu@...gle.com>,
Fazla Mehrab <a.mehrab@...edance.com>,
Chen Zhongjin <chenzhongjin@...wei.com>,
Puranjay Mohan <puranjay@...nel.org>,
Dylan Hatch <dylanbhatch@...gle.com>,
Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v4 54/63] objtool: Refactor prefix symbol creation code
The prefix symbol creation code currently ignores all errors, presumably
because some functions don't have the leading NOPs.
Shuffle the code around a bit, improve the error handling and document
why some errors are ignored.
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
tools/objtool/check.c | 59 ++++++++++++++++++++++-------
tools/objtool/elf.c | 17 ---------
tools/objtool/include/objtool/elf.h | 2 -
3 files changed, 46 insertions(+), 32 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6eaae3c007486..6a9ce090a2cde 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -15,6 +15,7 @@
#include <objtool/special.h>
#include <objtool/warn.h>
#include <objtool/checksum.h>
+#include <objtool/util.h>
#include <linux/objtool_types.h>
#include <linux/hashtable.h>
@@ -4243,37 +4244,71 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
return false;
}
-static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
+/*
+ * For FineIBT or kCFI, a certain number of bytes preceding the function may be
+ * NOPs. Those NOPs may be rewritten at runtime and executed, so give them a
+ * proper function name: __pfx_<func>.
+ *
+ * The NOPs may not exist for the following cases:
+ *
+ * - compiler cloned functions (*.cold, *.part0, etc)
+ * - asm functions created with inline asm or without SYM_FUNC_START()
+ *
+ * So return 0 if the NOPs are missing or the function already has a prefix
+ * symbol.
+ */
+static int create_prefix_symbol(struct objtool_file *file, struct symbol *func)
{
struct instruction *insn, *prev;
+ char name[SYM_NAME_LEN];
struct cfi_state *cfi;
- insn = find_insn(file, func->sec, func->offset);
- if (!insn)
+ if (!is_func_sym(func) || is_prefix_func(func) ||
+ func->cold || func->static_call_tramp)
+ return 0;
+
+ if ((strlen(func->name) + sizeof("__pfx_") > SYM_NAME_LEN)) {
+ WARN("%s: symbol name too long, can't create __pfx_ symbol",
+ func->name);
+ return 0;
+ }
+
+ if (snprintf_check(name, SYM_NAME_LEN, "__pfx_%s", func->name))
return -1;
+ insn = find_insn(file, func->sec, func->offset);
+ if (!insn) {
+ WARN("%s: can't find starting instruction", func->name);
+ return -1;
+ }
+
for (prev = prev_insn_same_sec(file, insn);
prev;
prev = prev_insn_same_sec(file, prev)) {
u64 offset;
if (prev->type != INSN_NOP)
- return -1;
+ return 0;
offset = func->offset - prev->offset;
if (offset > opts.prefix)
- return -1;
+ return 0;
if (offset < opts.prefix)
continue;
- elf_create_prefix_symbol(file->elf, func, opts.prefix);
+ if (!elf_create_symbol(file->elf, name, func->sec,
+ GELF_ST_BIND(func->sym.st_info),
+ GELF_ST_TYPE(func->sym.st_info),
+ prev->offset, opts.prefix))
+ return -1;
+
break;
}
if (!prev)
- return -1;
+ return 0;
if (!insn->cfi) {
/*
@@ -4291,7 +4326,7 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
return 0;
}
-static int add_prefix_symbols(struct objtool_file *file)
+static int create_prefix_symbols(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;
@@ -4301,10 +4336,8 @@ static int add_prefix_symbols(struct objtool_file *file)
continue;
sec_for_each_sym(sec, func) {
- if (!is_func_sym(func))
- continue;
-
- add_prefix_symbol(file, func);
+ if (create_prefix_symbol(file, func))
+ return -1;
}
}
@@ -4931,7 +4964,7 @@ int check(struct objtool_file *file)
}
if (opts.prefix) {
- ret = add_prefix_symbols(file);
+ ret = create_prefix_symbols(file);
if (ret)
goto out;
}
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index e1daae0630be9..4bb7ce994b6a7 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -942,23 +942,6 @@ struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec)
return sym;
}
-struct symbol *
-elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, size_t size)
-{
- size_t namelen = strlen(orig->name) + sizeof("__pfx_");
- char name[SYM_NAME_LEN];
- unsigned long offset;
-
- snprintf(name, namelen, "__pfx_%s", orig->name);
-
- offset = orig->sym.st_value - size;
-
- return elf_create_symbol(elf, name, orig->sec,
- GELF_ST_BIND(orig->sym.st_info),
- GELF_ST_TYPE(orig->sym.st_info),
- offset, size);
-}
-
struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
unsigned int reloc_idx, unsigned long offset,
struct symbol *sym, s64 addend, unsigned int type)
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index e2cd817fca522..60f844e43c5a2 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -148,8 +148,6 @@ struct symbol *elf_create_symbol(struct elf *elf, const char *name,
unsigned int type, unsigned long offset,
size_t size);
struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec);
-struct symbol *elf_create_prefix_symbol(struct elf *elf, struct symbol *orig,
- size_t size);
void *elf_add_data(struct elf *elf, struct section *sec, const void *data,
size_t size);
--
2.50.0
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