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Message-ID: <20240807220513.3100483-3-song@kernel.org>
Date: Wed, 7 Aug 2024 15:05:13 -0700
From: Song Liu <song@...nel.org>
To: live-patching@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org
Cc: jpoimboe@...nel.org,
jikos@...nel.org,
mbenes@...e.cz,
pmladek@...e.com,
joe.lawrence@...hat.com,
nathan@...nel.org,
morbo@...gle.com,
justinstitt@...gle.com,
mcgrof@...nel.org,
thunder.leizhen@...wei.com,
kees@...nel.org,
kernel-team@...a.com,
song@...nel.org,
mmaurer@...gle.com,
samitolvanen@...gle.com,
mhiramat@...nel.org,
rostedt@...dmis.org
Subject: [PATCH v3 2/2] kallsyms: Match symbols exactly with CONFIG_LTO_CLANG
With CONFIG_LTO_CLANG=y, the compiler may add .llvm.<hash> suffix to
function names to avoid duplication. APIs like kallsyms_lookup_name()
and kallsyms_on_each_match_symbol() tries to match these symbol names
without the .llvm.<hash> suffix, e.g., match "c_stop" with symbol
c_stop.llvm.17132674095431275852. This turned out to be problematic
for use cases that require exact match, for example, livepatch.
Fix this by making the APIs to match symbols exactly.
Also cleanup kallsyms_selftests accordingly.
Signed-off-by: Song Liu <song@...nel.org>
---
kernel/kallsyms.c | 55 +++++---------------------------------
kernel/kallsyms_selftest.c | 22 +--------------
2 files changed, 7 insertions(+), 70 deletions(-)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index fb2c77368d18..a9a0ca605d4a 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -160,38 +160,6 @@ unsigned long kallsyms_sym_address(int idx)
return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
}
-static void cleanup_symbol_name(char *s)
-{
- char *res;
-
- if (!IS_ENABLED(CONFIG_LTO_CLANG))
- return;
-
- /*
- * LLVM appends various suffixes for local functions and variables that
- * must be promoted to global scope as part of LTO. This can break
- * hooking of static functions with kprobes. '.' is not a valid
- * character in an identifier in C. Suffixes only in LLVM LTO observed:
- * - foo.llvm.[0-9a-f]+
- */
- res = strstr(s, ".llvm.");
- if (res)
- *res = '\0';
-
- return;
-}
-
-static int compare_symbol_name(const char *name, char *namebuf)
-{
- /* The kallsyms_seqs_of_names is sorted based on names after
- * cleanup_symbol_name() (see scripts/kallsyms.c) if clang lto is enabled.
- * To ensure correct bisection in kallsyms_lookup_names(), do
- * cleanup_symbol_name(namebuf) before comparing name and namebuf.
- */
- cleanup_symbol_name(namebuf);
- return strcmp(name, namebuf);
-}
-
static unsigned int get_symbol_seq(int index)
{
unsigned int i, seq = 0;
@@ -219,7 +187,7 @@ static int kallsyms_lookup_names(const char *name,
seq = get_symbol_seq(mid);
off = get_symbol_offset(seq);
kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
- ret = compare_symbol_name(name, namebuf);
+ ret = strcmp(name, namebuf);
if (ret > 0)
low = mid + 1;
else if (ret < 0)
@@ -236,7 +204,7 @@ static int kallsyms_lookup_names(const char *name,
seq = get_symbol_seq(low - 1);
off = get_symbol_offset(seq);
kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
- if (compare_symbol_name(name, namebuf))
+ if (strcmp(name, namebuf))
break;
low--;
}
@@ -248,7 +216,7 @@ static int kallsyms_lookup_names(const char *name,
seq = get_symbol_seq(high + 1);
off = get_symbol_offset(seq);
kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
- if (compare_symbol_name(name, namebuf))
+ if (strcmp(name, namebuf))
break;
high++;
}
@@ -407,8 +375,7 @@ static int kallsyms_lookup_buildid(unsigned long addr,
if (modbuildid)
*modbuildid = NULL;
- ret = strlen(namebuf);
- goto found;
+ return strlen(namebuf);
}
/* See if it's in a module or a BPF JITed image. */
@@ -422,8 +389,6 @@ static int kallsyms_lookup_buildid(unsigned long addr,
ret = ftrace_mod_address_lookup(addr, symbolsize,
offset, modname, namebuf);
-found:
- cleanup_symbol_name(namebuf);
return ret;
}
@@ -450,8 +415,6 @@ const char *kallsyms_lookup(unsigned long addr,
int lookup_symbol_name(unsigned long addr, char *symname)
{
- int res;
-
symname[0] = '\0';
symname[KSYM_NAME_LEN - 1] = '\0';
@@ -462,16 +425,10 @@ int lookup_symbol_name(unsigned long addr, char *symname)
/* Grab name */
kallsyms_expand_symbol(get_symbol_offset(pos),
symname, KSYM_NAME_LEN);
- goto found;
+ return 0;
}
/* See if it's in a module. */
- res = lookup_module_symbol_name(addr, symname);
- if (res)
- return res;
-
-found:
- cleanup_symbol_name(symname);
- return 0;
+ return lookup_module_symbol_name(addr, symname);
}
/* Look up a kernel symbol and return it in a text buffer. */
diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c
index 2f84896a7bcb..873f7c445488 100644
--- a/kernel/kallsyms_selftest.c
+++ b/kernel/kallsyms_selftest.c
@@ -187,31 +187,11 @@ static void test_perf_kallsyms_lookup_name(void)
stat.min, stat.max, div_u64(stat.sum, stat.real_cnt));
}
-static bool match_cleanup_name(const char *s, const char *name)
-{
- char *p;
- int len;
-
- if (!IS_ENABLED(CONFIG_LTO_CLANG))
- return false;
-
- p = strstr(s, ".llvm.");
- if (!p)
- return false;
-
- len = strlen(name);
- if (p - s != len)
- return false;
-
- return !strncmp(s, name, len);
-}
-
static int find_symbol(void *data, const char *name, unsigned long addr)
{
struct test_stat *stat = (struct test_stat *)data;
- if (strcmp(name, stat->name) == 0 ||
- (!stat->perf && match_cleanup_name(name, stat->name))) {
+ if (!strcmp(name, stat->name)) {
stat->real_cnt++;
stat->addr = addr;
--
2.43.5
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