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Message-ID: <140f6ddac534bcbf3a7e3c096bf15588ada7ae3c.1746821544.git.jpoimboe@kernel.org>
Date: Fri, 9 May 2025 13:17:17 -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>
Subject: [PATCH v2 53/62] objtool/klp: Add --debug option to show cloning decisions
Add a --debug option to klp diff which prints cloning decisions and an
indented dependency tree for all cloned symbols and relocations. This
helps visualize which symbols and relocations were included and why.
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
tools/objtool/include/objtool/warn.h | 21 ++++++++
tools/objtool/klp-diff.c | 75 ++++++++++++++++++++++++++++
tools/objtool/objtool.c | 3 ++
3 files changed, 99 insertions(+)
diff --git a/tools/objtool/include/objtool/warn.h b/tools/objtool/include/objtool/warn.h
index 29173a1368d7..e88322d97573 100644
--- a/tools/objtool/include/objtool/warn.h
+++ b/tools/objtool/include/objtool/warn.h
@@ -102,6 +102,10 @@ static inline char *offstr(struct section *sec, unsigned long offset)
#define ERROR_FUNC(sec, offset, format, ...) __WARN_FUNC(ERROR_STR, sec, offset, format, ##__VA_ARGS__)
#define ERROR_INSN(insn, format, ...) WARN_FUNC(insn->sec, insn->offset, format, ##__VA_ARGS__)
+extern bool debug;
+extern int indent;
+
+static inline void unindent(int *unused) { indent--; }
#define __dbg(format, ...) \
fprintf(stderr, \
@@ -110,6 +114,23 @@ static inline char *offstr(struct section *sec, unsigned long offset)
objname ? ": " : "", \
##__VA_ARGS__)
+#define dbg(args...) \
+({ \
+ if (unlikely(debug)) \
+ __dbg(args); \
+})
+
+#define __dbg_indent(format, ...) \
+({ \
+ if (unlikely(debug)) \
+ __dbg("%*s" format, indent * 8, "", ##__VA_ARGS__); \
+})
+
+#define dbg_indent(args...) \
+ int __attribute__((cleanup(unindent))) __dummy_##__COUNTER__; \
+ __dbg_indent(args); \
+ indent++
+
#define dbg_checksum(func, insn, checksum) \
({ \
if (unlikely(insn->sym && insn->sym->pfunc && \
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index f17e4809ad4b..144525e74da3 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -36,6 +36,8 @@ static const char * const klp_diff_usage[] = {
};
static const struct option klp_diff_options[] = {
+ OPT_GROUP("Options:"),
+ OPT_BOOLEAN('d', "debug", &debug, "enable debug output"),
OPT_END(),
};
@@ -46,6 +48,38 @@ static inline u32 str_hash(const char *str)
return jhash(str, strlen(str), 0);
}
+static char *escape_str(const char *orig)
+{
+ size_t len = 0;
+ const char *a;
+ char *b, *new;
+
+ for (a = orig; *a; a++) {
+ switch (*a) {
+ case '\001': len += 5; break;
+ case '\n':
+ case '\t': len += 2; break;
+ default: len++;
+ }
+ }
+
+ new = malloc(len + 1);
+ if (!new)
+ return NULL;
+
+ for (a = orig, b = new; *a; a++) {
+ switch (*a) {
+ case '\001': memcpy(b, "<SOH>", 5); b += 5; break;
+ case '\n': *b++ = '\\'; *b++ = 'n'; break;
+ case '\t': *b++ = '\\'; *b++ = 't'; break;
+ default: *b++ = *a;
+ }
+ }
+
+ *b = '\0';
+ return new;
+}
+
/*
* Do a sanity check to make sure the changed object was built with
* -ffunction-sections and -fdata-sections.
@@ -516,6 +550,28 @@ static struct symbol *__clone_symbol(struct elf *elf, struct symbol *patched_sym
return out_sym;
}
+static const char *sym_type(struct symbol *sym)
+{
+ switch (sym->type) {
+ case STT_NOTYPE: return "NOTYPE";
+ case STT_OBJECT: return "OBJECT";
+ case STT_FUNC: return "FUNC";
+ case STT_SECTION: return "SECTION";
+ case STT_FILE: return "FILE";
+ default: return "UNKNOWN";
+ }
+}
+
+static const char *sym_bind(struct symbol *sym)
+{
+ switch (sym->bind) {
+ case STB_LOCAL : return "LOCAL";
+ case STB_GLOBAL: return "GLOBAL";
+ case STB_WEAK: return "WEAK";
+ default: return "UNKNOWN";
+ }
+}
+
/*
* Copy a symbol to the output object, optionally including its data and
* relocations.
@@ -528,6 +584,8 @@ static struct symbol *clone_symbol(struct elfs *e, struct symbol *patched_sym,
if (patched_sym->clone)
return patched_sym->clone;
+ dbg_indent("%s%s", patched_sym->name, data_too ? " [+DATA]" : "");
+
/* Make sure the prefix gets cloned first */
if (is_func_sym(patched_sym) && data_too) {
pfx = get_func_prefix(patched_sym);
@@ -889,6 +947,8 @@ static int clone_reloc_klp(struct elfs *e, struct reloc *patched_reloc,
klp_sym = find_symbol_by_name(e->out, sym_name);
if (!klp_sym) {
+ __dbg_indent("%s", sym_name);
+
/* STB_WEAK: avoid modpost undefined symbol warnings */
klp_sym = elf_create_symbol(e->out, sym_name, NULL,
STB_WEAK, patched_sym->type, 0, 0);
@@ -937,6 +997,17 @@ static int clone_reloc_klp(struct elfs *e, struct reloc *patched_reloc,
return 0;
}
+#define dbg_clone_reloc(sec, offset, patched_sym, addend, export, klp) \
+ dbg_indent("%s+0x%lx: %s%s0x%lx [%s%s%s%s%s%s]", \
+ sec->name, offset, patched_sym->name, \
+ addend >= 0 ? "+" : "-", labs(addend), \
+ sym_type(patched_sym), \
+ patched_sym->type == STT_SECTION ? "" : " ", \
+ patched_sym->type == STT_SECTION ? "" : sym_bind(patched_sym), \
+ is_undef_sym(patched_sym) ? " UNDEF" : "", \
+ export ? " EXPORTED" : "", \
+ klp ? " KLP" : "")
+
/* Copy a reloc and its symbol to the output object */
static int clone_reloc(struct elfs *e, struct reloc *patched_reloc,
struct section *sec, unsigned long offset)
@@ -956,6 +1027,8 @@ static int clone_reloc(struct elfs *e, struct reloc *patched_reloc,
klp = klp_reloc_needed(patched_reloc);
+ dbg_clone_reloc(sec, offset, patched_sym, addend, export, klp);
+
if (klp) {
if (clone_reloc_klp(e, patched_reloc, sec, offset, export))
return -1;
@@ -987,6 +1060,8 @@ static int clone_reloc(struct elfs *e, struct reloc *patched_reloc,
if (is_string_sec(patched_sym->sec)) {
const char *str = patched_sym->sec->data->d_buf + addend;
+ __dbg_indent("\"%s\"", escape_str(str));
+
addend = elf_add_string(e->out, out_sym->sec, str);
if (addend == -1)
return -1;
diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index c8f611c1320d..3c26ed561c7e 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -16,6 +16,9 @@
#include <objtool/objtool.h>
#include <objtool/warn.h>
+bool debug;
+int indent;
+
static struct objtool_file file;
struct objtool_file *objtool_open_read(const char *filename)
--
2.49.0
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