Re: [PATCH v4 05/10] objtool: Handle unreachable entry of rodata

From: Tiezhu Yang
Date: Tue Nov 26 2024 - 06:04:48 EST


On 11/26/2024 03:25 PM, Josh Poimboeuf wrote:
On Fri, Nov 22, 2024 at 12:50:00PM +0800, Tiezhu Yang wrote:
When compling with Clang on LoongArch, there exists unreachable entry of
rodata which points to a position after the function return instruction,
this is generated by compiler to fill the non-existent switch case, just
skip the entry when parsing the relocation section of rodata.

This is preparation for later patch on LoongArch, there is no effect for
the other archs with this patch.

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
tools/objtool/check.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8733ca620cca..b21e47d8d3d1 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2144,6 +2144,13 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
if (!dest_insn)
break;

+ /* Handle the special cases compiled with Clang on LoongArch */
+ if (file->elf->ehdr.e_machine == EM_LOONGARCH && reloc->sym->type == STT_SECTION &&
+ (!insn_func(dest_insn) || insn_func(dest_insn)->pfunc != pfunc)) {
+ prev_offset = reloc_offset(reloc);
+ continue;

Are you sure this is specific to loongarch?

I am not sure, I only found this issue on LoongArch compiled with Clang,
but I think there is no effect if make it generic, like this:

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f7586f82b967..87302e6fc07f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2103,9 +2103,10 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
if (!dest_insn)
break;

- /* Make sure the destination is in the same function: */
- if (!insn_func(dest_insn) || insn_func(dest_insn)->pfunc != pfunc)
- break;
+ if (!insn_func(dest_insn) || insn_func(dest_insn)->pfunc != pfunc) {
+ prev_offset = reloc_offset(reloc);
+ continue;
+ }

alt = malloc(sizeof(*alt));
if (!alt) {

If you are OK, I will modify it.

Thanks,
Tiezhu