From: Alexandre Chartre Date: Fri, 21 Nov 2025 09:53:25 +0000 (+0100) Subject: objtool: Improve tracing of alternative instructions X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=350c7ab8577a32c101a097f4c072220d9ce64f3b;p=thirdparty%2Fkernel%2Flinux.git objtool: Improve tracing of alternative instructions When tracing function validation, improve the reporting of alternative instruction by more clearly showing the different alternatives beginning and end. Signed-off-by: Alexandre Chartre Signed-off-by: Peter Zijlstra (Intel) Acked-by: Josh Poimboeuf Link: https://patch.msgid.link/20251121095340.464045-16-alexandre.chartre@oracle.com --- diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 93aaa4b5dce0e..442b655e3f25f 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -3564,7 +3564,7 @@ static bool skip_alt_group(struct instruction *insn) /* ANNOTATE_IGNORE_ALTERNATIVE */ if (insn->alt_group->ignore) { - TRACE_INSN(insn, "alt group ignored"); + TRACE_ALT(insn, "alt group ignored"); return true; } @@ -3680,8 +3680,9 @@ static int validate_insn(struct objtool_file *file, struct symbol *func, struct instruction *prev_insn, struct instruction *next_insn, bool *dead_end) { - /* prev_state is not used if there is no disassembly support */ + /* prev_state and alt_name are not used if there is no disassembly support */ struct insn_state prev_state __maybe_unused; + char *alt_name __maybe_unused = NULL; struct alternative *alt; u8 visited; int ret; @@ -3768,23 +3769,16 @@ static int validate_insn(struct objtool_file *file, struct symbol *func, return 1; if (insn->alts) { - int i, num_alts; - - num_alts = 0; - for (alt = insn->alts; alt; alt = alt->next) - num_alts++; - - i = 1; for (alt = insn->alts; alt; alt = alt->next) { - TRACE_INSN(insn, "alternative %d/%d", i, num_alts); + TRACE_ALT_BEGIN(insn, alt, alt_name); ret = validate_branch(file, func, alt->insn, *statep); + TRACE_ALT_END(insn, alt, alt_name); if (ret) { BT_INSN(insn, "(alt)"); return ret; } - i++; } - TRACE_INSN(insn, "alternative DEFAULT"); + TRACE_ALT_INFO_NOADDR(insn, "/ ", "DEFAULT"); } if (skip_alt_group(insn)) diff --git a/tools/objtool/include/objtool/trace.h b/tools/objtool/include/objtool/trace.h index 33fe9c6acb4fd..70b574366797b 100644 --- a/tools/objtool/include/objtool/trace.h +++ b/tools/objtool/include/objtool/trace.h @@ -19,11 +19,26 @@ extern int trace_depth; fprintf(stderr, fmt, ##__VA_ARGS__); \ }) +/* + * Print the instruction address and a message. The instruction + * itself is not printed. + */ +#define TRACE_ADDR(insn, fmt, ...) \ +({ \ + if (trace) { \ + disas_print_info(stderr, insn, trace_depth - 1, \ + fmt "\n", ##__VA_ARGS__); \ + } \ +}) + +/* + * Print the instruction address, the instruction and a message. + */ #define TRACE_INSN(insn, fmt, ...) \ ({ \ if (trace) { \ disas_print_insn(stderr, objtool_disas_ctx, \ - insn, trace_depth - 1, \ + insn, trace_depth - 1, \ fmt, ##__VA_ARGS__); \ fprintf(stderr, "\n"); \ insn->trace = 1; \ @@ -36,6 +51,37 @@ extern int trace_depth; trace_insn_state(insn, sprev, snext); \ }) +#define TRACE_ALT_FMT(pfx, fmt) pfx "<%s.%lx> " fmt +#define TRACE_ALT_ARG(insn) disas_alt_type_name(insn), (insn)->offset + +#define TRACE_ALT(insn, fmt, ...) \ + TRACE_INSN(insn, TRACE_ALT_FMT("", fmt), \ + TRACE_ALT_ARG(insn), ##__VA_ARGS__) + +#define TRACE_ALT_INFO(insn, pfx, fmt, ...) \ + TRACE_ADDR(insn, TRACE_ALT_FMT(pfx, fmt), \ + TRACE_ALT_ARG(insn), ##__VA_ARGS__) + +#define TRACE_ALT_INFO_NOADDR(insn, pfx, fmt, ...) \ + TRACE_ADDR(NULL, TRACE_ALT_FMT(pfx, fmt), \ + TRACE_ALT_ARG(insn), ##__VA_ARGS__) + +#define TRACE_ALT_BEGIN(insn, alt, alt_name) \ +({ \ + if (trace) { \ + alt_name = disas_alt_name(alt); \ + trace_alt_begin(insn, alt, alt_name); \ + } \ +}) + +#define TRACE_ALT_END(insn, alt, alt_name) \ +({ \ + if (trace) { \ + trace_alt_end(insn, alt, alt_name); \ + free(alt_name); \ + } \ +}) + static inline void trace_enable(void) { trace = true; @@ -61,17 +107,34 @@ static inline void trace_depth_dec(void) void trace_insn_state(struct instruction *insn, struct insn_state *sprev, struct insn_state *snext); +void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt, + char *alt_name); +void trace_alt_end(struct instruction *orig_insn, struct alternative *alt, + char *alt_name); #else /* DISAS */ #define TRACE(fmt, ...) ({}) +#define TRACE_ADDR(insn, fmt, ...) ({}) #define TRACE_INSN(insn, fmt, ...) ({}) #define TRACE_INSN_STATE(insn, sprev, snext) ({}) +#define TRACE_ALT(insn, fmt, ...) ({}) +#define TRACE_ALT_INFO(insn, fmt, ...) ({}) +#define TRACE_ALT_INFO_NOADDR(insn, fmt, ...) ({}) +#define TRACE_ALT_BEGIN(insn, alt, alt_name) ({}) +#define TRACE_ALT_END(insn, alt, alt_name) ({}) + static inline void trace_enable(void) {} static inline void trace_disable(void) {} static inline void trace_depth_inc(void) {} static inline void trace_depth_dec(void) {} +static inline void trace_alt_begin(struct instruction *orig_insn, + struct alternative *alt, + char *alt_name) {}; +static inline void trace_alt_end(struct instruction *orig_insn, + struct alternative *alt, + char *alt_name) {}; #endif diff --git a/tools/objtool/trace.c b/tools/objtool/trace.c index d70d47081e82d..5dec44dab781c 100644 --- a/tools/objtool/trace.c +++ b/tools/objtool/trace.c @@ -146,3 +146,58 @@ void trace_insn_state(struct instruction *insn, struct insn_state *sprev, insn->trace = 1; } + +void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt, + char *alt_name) +{ + struct instruction *alt_insn; + char suffix[2]; + + alt_insn = alt->insn; + + if (alt->type == ALT_TYPE_EX_TABLE) { + /* + * When there is an exception table then the instruction + * at the original location is executed but it can cause + * an exception. In that case, the execution will be + * redirected to the alternative instruction. + * + * The instruction at the original location can have + * instruction alternatives, so we just print the location + * of the instruction that can cause the exception and + * not the instruction itself. + */ + TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s for instruction at 0x%lx <%s+0x%lx>", + alt_name, + orig_insn->offset, orig_insn->sym->name, + orig_insn->offset - orig_insn->sym->offset); + } else { + TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s", alt_name); + } + + if (alt->type == ALT_TYPE_JUMP_TABLE) { + /* + * For a jump alternative, if the default instruction is + * a NOP then it is replaced with the jmp instruction, + * otherwise it is replaced with a NOP instruction. + */ + trace_depth++; + if (orig_insn->type == INSN_NOP) { + suffix[0] = (orig_insn->len == 5) ? 'q' : '\0'; + TRACE_ADDR(orig_insn, "jmp%-3s %lx <%s+0x%lx>", suffix, + alt_insn->offset, alt_insn->sym->name, + alt_insn->offset - alt_insn->sym->offset); + } else { + TRACE_ADDR(orig_insn, "nop%d", orig_insn->len); + trace_depth--; + } + } +} + +void trace_alt_end(struct instruction *orig_insn, struct alternative *alt, + char *alt_name) +{ + if (alt->type == ALT_TYPE_JUMP_TABLE && orig_insn->type == INSN_NOP) + trace_depth--; + TRACE_ALT_INFO_NOADDR(orig_insn, "\\ ", "%s", alt_name); +}