mirror of
https://gitee.com/open-loongarch/linux-6.12.git
synced 2026-10-27 05:27:12 +08:00
Tiezhu Yang
c095d3e54a
The objtool program need to analysis the control flow of each object file generated by compiler toolchain, it needs to know all the locations that a branch instruction may jump into, if a jump table is used, objtool has to correlate the jump instruction with the table. On x86 (which is the only port supported by objtool before LoongArch), there is a relocation type on the jump instruction and directly points to the table. But on LoongArch, the relocation is on another kind of instruction prior to the jump instruction, and also with scheduling it is not very easy to tell the offset of that instruction from the jump instruction. Furthermore, because LoongArch has -fsection-anchors (often enabled at -O1 or above) the relocation may actually points to a section anchor instead of the table itself. The good news is that after continuous analysis and discussion, at last a GCC patch "LoongArch: Add support to annotate tablejump" and a Clang patch "[LoongArch] Add options for annotate tablejump" have been merged into the upstream mainline, the compiler changes make life much easier for switch table support of objtool on LoongArch. By now, there is an additional section ".discard.tablejump_annotate" to store the jump info as pairs of addresses, each pair contains the address of jump instruction and the address of jump table. In order to find switch table, it is easy to parse the relocation section ".rela.discard.tablejump_annotate" to get table_sec and table_offset, the rest process is somehow like x86. Link: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=0ee028f55640 Link: https://github.com/llvm/llvm-project/commit/4c2c17756739 Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn> Signed-off-by: michael <michael5hzg@gmail.com> Signed-off-by: maoxiaochuan <maoxiaochuan@loongson.cn>