objtool: Trim trailing NOPs in alternative
When disassembling alternatives replace trailing NOPs with a single indication of the number of bytes covered with NOPs. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-31-alexandre.chartre@oracle.com
This commit is contained in:
Alexandre Chartre
Peter Zijlstra
parent
aff95e0d4e
commit
c0a67900dc
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@ -52,6 +52,7 @@ struct disas_alt {
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struct {
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char *str; /* instruction string */
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int offset; /* instruction offset */
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int nops; /* number of nops */
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} insn[DISAS_ALT_INSN_MAX]; /* alternative instructions */
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int insn_idx; /* index of the next instruction to print */
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};
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@ -727,7 +728,7 @@ static int disas_alt_init(struct disas_alt *dalt,
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}
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static int disas_alt_add_insn(struct disas_alt *dalt, int index, char *insn_str,
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int offset)
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int offset, int nops)
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{
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int len;
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@ -740,6 +741,7 @@ static int disas_alt_add_insn(struct disas_alt *dalt, int index, char *insn_str,
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len = strlen(insn_str);
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dalt->insn[index].str = insn_str;
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dalt->insn[index].offset = offset;
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dalt->insn[index].nops = nops;
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if (len > dalt->width)
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dalt->width = len;
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@ -752,6 +754,7 @@ static int disas_alt_jump(struct disas_alt *dalt)
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struct instruction *dest_insn;
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char suffix[2] = { 0 };
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char *str;
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int nops;
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orig_insn = dalt->orig_insn;
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dest_insn = dalt->alt->insn;
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@ -762,14 +765,16 @@ static int disas_alt_jump(struct disas_alt *dalt)
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str = strfmt("jmp%-3s %lx <%s+0x%lx>", suffix,
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dest_insn->offset, dest_insn->sym->name,
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dest_insn->offset - dest_insn->sym->offset);
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nops = 0;
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} else {
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str = strfmt("nop%d", orig_insn->len);
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nops = orig_insn->len;
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}
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if (!str)
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return -1;
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disas_alt_add_insn(dalt, 0, str, 0);
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disas_alt_add_insn(dalt, 0, str, 0, nops);
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return 1;
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}
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@ -789,7 +794,7 @@ static int disas_alt_extable(struct disas_alt *dalt)
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if (!str)
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return -1;
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disas_alt_add_insn(dalt, 0, str, 0);
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disas_alt_add_insn(dalt, 0, str, 0, 0);
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return 1;
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}
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@ -805,11 +810,13 @@ static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt)
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int offset;
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char *str;
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int count;
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int nops;
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int err;
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file = dctx->file;
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count = 0;
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offset = 0;
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nops = 0;
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alt_for_each_insn(file, DALT_GROUP(dalt), insn) {
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@ -818,7 +825,8 @@ static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt)
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if (!str)
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return -1;
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err = disas_alt_add_insn(dalt, count, str, offset);
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nops = insn->type == INSN_NOP ? insn->len : 0;
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err = disas_alt_add_insn(dalt, count, str, offset, nops);
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if (err)
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break;
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offset += insn->len;
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@ -834,6 +842,7 @@ static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt)
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static int disas_alt_default(struct disas_context *dctx, struct disas_alt *dalt)
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{
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char *str;
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int nops;
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int err;
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if (DALT_GROUP(dalt))
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@ -849,7 +858,8 @@ static int disas_alt_default(struct disas_context *dctx, struct disas_alt *dalt)
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str = strdup(disas_result(dctx));
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if (!str)
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return -1;
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err = disas_alt_add_insn(dalt, 0, str, 0);
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nops = dalt->orig_insn->type == INSN_NOP ? dalt->orig_insn->len : 0;
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err = disas_alt_add_insn(dalt, 0, str, 0, nops);
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if (err)
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return -1;
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@ -995,6 +1005,62 @@ static void disas_alt_print_compact(char *alt_name, struct disas_alt *dalts,
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}
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}
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/*
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* Trim NOPs in alternatives. This replaces trailing NOPs in alternatives
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* with a single indication of the number of bytes covered with NOPs.
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*
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* Return the maximum numbers of instructions in all alternatives after
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* trailing NOPs have been trimmed.
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*/
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static int disas_alt_trim_nops(struct disas_alt *dalts, int alt_count,
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int insn_count)
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{
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struct disas_alt *dalt;
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int nops_count;
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const char *s;
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int offset;
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int count;
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int nops;
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int i, j;
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count = 0;
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for (i = 0; i < alt_count; i++) {
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offset = 0;
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nops = 0;
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nops_count = 0;
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dalt = &dalts[i];
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for (j = insn_count - 1; j >= 0; j--) {
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if (!dalt->insn[j].str || !dalt->insn[j].nops)
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break;
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offset = dalt->insn[j].offset;
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free(dalt->insn[j].str);
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dalt->insn[j].offset = 0;
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dalt->insn[j].str = NULL;
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nops += dalt->insn[j].nops;
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nops_count++;
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}
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/*
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* All trailing NOPs have been removed. If there was a single
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* NOP instruction then re-add it. If there was a block of
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* NOPs then indicate the number of bytes than the block
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* covers (nop*<number-of-bytes>).
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*/
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if (nops_count) {
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s = nops_count == 1 ? "" : "*";
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dalt->insn[j + 1].str = strfmt("nop%s%d", s, nops);
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dalt->insn[j + 1].offset = offset;
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dalt->insn[j + 1].nops = nops;
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j++;
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}
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if (j > count)
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count = j;
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}
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return count + 1;
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}
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/*
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* Disassemble an alternative.
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*
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@ -1083,6 +1149,8 @@ static void *disas_alt(struct disas_context *dctx,
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* Print default and non-default alternatives.
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*/
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insn_count = disas_alt_trim_nops(dalts, alt_count, insn_count);
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if (opts.wide)
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disas_alt_print_wide(alt_name, dalts, alt_count, insn_count);
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else
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