Messages in this thread Patch in this message | | | Date | Wed, 26 Jun 2019 22:56:23 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v3 2/4] objtool: Add support for C jump tables |
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On Wed, Jun 26, 2019 at 10:44:47PM -0500, Josh Poimboeuf wrote: > > > How about the following approach instead? This is the only other way I > > > can think of to annotate a jump table so that objtool can distinguish > > > it: > > > > > > #define __annotate_jump_table __section(".jump_table.rodata") > > > > > > Then bpf would just need the following: > > > > > > - static const void *jumptable[256] = { > > > + static const void __annotate_jump_table *jumptable[256] = { > > > > > > This would be less magical and fragile than my original approach. > > > > > > I think the jump table would still be placed with all the other rodata, > > > like before, because the vmlinux linker script recognizes the section > > > ".rodata" suffix and bundles them all together. > > > > I like it if that works :) > > Definitely cleaner. > > May be a bit more linker script magic would be necessary, > > but hopefully not. > > And no need to rely on gcc style of mangling static vars.
The last patch was based weird, this one's based on upstream. Will test tomorrow.
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 8aaf7cd026b0..84212bcb5015 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 enable objtool to follow the code flow */ +#define __annotate_jump_table __section(".jump_table.rodata") + #else #define annotate_reachable() #define annotate_unreachable() +#define __annotate_jump_table #endif #ifndef ASM_UNREACHABLE diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 080e2bb644cc..e67977e22967 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1299,7 +1299,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack) { #define BPF_INSN_2_LBL(x, y) [BPF_##x | BPF_##y] = &&x##_##y #define BPF_INSN_3_LBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = &&x##_##y##_##z - static const void *jumptable[256] = { + static const void __annotate_jump_table *jumptable[256] = { [0 ... 255] = &&default_label, /* Now overwrite non-defaults ... */ BPF_INSN_MAP(BPF_INSN_2_LBL, BPF_INSN_3_LBL), @@ -1558,7 +1558,6 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack) BUG_ON(1); return 0; } -STACK_FRAME_NON_STANDARD(___bpf_prog_run); /* jump table */ #define PROG_NAME(stack_size) __bpf_prog_run##stack_size #define DEFINE_BPF_PROG_RUN(stack_size) \ diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 172f99195726..6ade2b32f484 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 ".jump_table.rodata" + 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.<func>: same, if -fdata-sections is being used + * - .jump_table.rodata: 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; }
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