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. For the jump table of switch cases, 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, it can parse the additional section ".discard.tablejump_annotate" which stores the jump info as pairs of addresses, each pair contains the address of jump instruction and the address of jump table. For the jump table of computed gotos, it is indeed not easy to implement in the compiler, especially if there is more than one computed goto in a function such as ___bpf_prog_run(). objdump kernel/bpf/core.o shows that there are many table jump instructions in ___bpf_prog_run(), but there are no relocations on the table jump instructions and to the table directly on LoongArch. Without the help of compiler, in order to figure out the address of goto table for the special case of ___bpf_prog_run(), since the instruction sequence is relatively single and stable, it makes sense to add a helper find_reloc_of_rodata_c_jump_table() to find the relocation which points to the section ".rodata..c_jump_table". If find_reloc_by_table_annotate() failed, it means there is no relocation info of switch table address in ".rela.discard.tablejump_annotate", then objtool may find the relocation info of goto table ".rodata..c_jump_table" with find_reloc_of_rodata_c_jump_table(). Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> --- tools/objtool/arch/loongarch/special.c | 32 ++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-) diff --git a/tools/objtool/arch/loongarch/special.c b/tools/objtool/arch/loongarch/special.c index 4fa6877d5b2b..27c6473608f3 100644 --- a/tools/objtool/arch/loongarch/special.c +++ b/tools/objtool/arch/loongarch/special.c @@ -116,6 +116,30 @@ static struct reloc *find_reloc_by_table_annotate(struct objtool_file *file, return NULL; } +static struct reloc *find_reloc_of_rodata_c_jump_table(struct section *sec, + unsigned long offset, + unsigned long *table_size) +{ + struct section *rsec; + struct reloc *reloc; + + rsec = sec->rsec; + if (!rsec) + return NULL; + + for_each_reloc(rsec, reloc) { + if (reloc_offset(reloc) > offset) + break; + + if (!strncmp(reloc->sym->sec->name, ".rodata..c_jump_table", 21)) { + *table_size = 0; + return reloc; + } + } + + return NULL; +} + struct reloc *arch_find_switch_table(struct objtool_file *file, struct instruction *insn, unsigned long *table_size) @@ -126,8 +150,12 @@ struct reloc *arch_find_switch_table(struct objtool_file *file, unsigned long table_offset; annotate_reloc = find_reloc_by_table_annotate(file, insn, table_size); - if (!annotate_reloc) - return NULL; + if (!annotate_reloc) { + annotate_reloc = find_reloc_of_rodata_c_jump_table( + insn->sec, insn->offset, table_size); + if (!annotate_reloc) + return NULL; + } table_sec = annotate_reloc->sym->sec; table_offset = annotate_reloc->sym->offset + reloc_addend(annotate_reloc); -- 2.42.0