From 87b512def792579641499d9bef1d640994ea9c18 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 27 Jun 2019 20:50:46 -0500 Subject: [PATCH] objtool: Add support for C jump tables Objtool doesn't know how to read C jump tables, so it has to whitelist functions which use them, causing missing ORC unwinder data for such functions, e.g. ___bpf_prog_run(). C jump tables are very similar to GCC switch jump tables, which objtool already knows how to read. So adding support for C jump tables is easy. It just needs to be able to find the tables and distinguish them from other data. To allow the jump tables to be found, create an __annotate_jump_table macro which can be used to annotate them. The annotation is done by placing the jump table in an .rodata..c_jump_table section. The '.rodata' prefix ensures that the data will be placed in the rodata section by the vmlinux linker script. The double periods are part of an existing convention which distinguishes kernel sections from GCC sections. Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Song Liu Cc: Kairui Song Cc: Steven Rostedt Cc: Borislav Petkov Cc: Alexei Starovoitov Cc: Daniel Borkmann Link: https://lkml.kernel.org/r/0ba2ca30442b16b97165992381ce643dc27b3d1a.1561685471.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 5 +++++ tools/objtool/check.c | 27 ++++++++++++++++++++------- 2 files changed, 25 insertions(+), 7 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 8aaf7cd026b0..f0fd5636fddb 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -116,9 +116,14 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, ".pushsection .discard.unreachable\n\t" \ ".long 999b - .\n\t" \ ".popsection\n\t" + +/* Annotate a C jump table to allow objtool to follow the code flow */ +#define __annotate_jump_table __section(".rodata..c_jump_table") + #else #define annotate_reachable() #define annotate_unreachable() +#define __annotate_jump_table #endif #ifndef ASM_UNREACHABLE diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 172f99195726..27818a93f0b1 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -18,6 +18,8 @@ #define FAKE_JUMP_OFFSET -1 +#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table" + struct alternative { struct list_head list; struct instruction *insn; @@ -1035,9 +1037,15 @@ static struct rela *find_switch_table(struct objtool_file *file, /* * Make sure the .rodata address isn't associated with a - * symbol. gcc jump tables are anonymous data. + * symbol. GCC jump tables are anonymous data. + * + * Also support C jump tables which are in the same format as + * switch jump tables. For objtool to recognize them, they + * need to be placed in the C_JUMP_TABLE_SECTION section. They + * have symbols associated with them. */ - if (find_symbol_containing(rodata_sec, table_offset)) + if (find_symbol_containing(rodata_sec, table_offset) && + strcmp(rodata_sec->name, C_JUMP_TABLE_SECTION)) continue; rodata_rela = find_rela_by_dest(rodata_sec, table_offset); @@ -1277,13 +1285,18 @@ static void mark_rodata(struct objtool_file *file) bool found = false; /* - * This searches for the .rodata section or multiple .rodata.func_name - * sections if -fdata-sections is being used. The .str.1.1 and .str.1.8 - * rodata sections are ignored as they don't contain jump tables. + * Search for the following rodata sections, each of which can + * potentially contain jump tables: + * + * - .rodata: can contain GCC switch tables + * - .rodata.: same, if -fdata-sections is being used + * - .rodata..c_jump_table: contains C annotated jump tables + * + * .rodata.str1.* sections are ignored; they don't contain jump tables. */ for_each_sec(file, sec) { - if (!strncmp(sec->name, ".rodata", 7) && - !strstr(sec->name, ".str1.")) { + if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) || + !strcmp(sec->name, C_JUMP_TABLE_SECTION)) { sec->rodata = true; found = true; } -- 2.20.1