Commit c0a67900 authored by Alexandre Chartre's avatar Alexandre Chartre Committed by Peter Zijlstra
Browse files

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: default avatarAlexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Link: https://patch.msgid.link/20251121095340.464045-31-alexandre.chartre@oracle.com
parent aff95e0d

tools/objtool/disas.c

+73 −5
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ struct disas_alt { 
	struct {

		char *str;			/* instruction string */

		int offset;			/* instruction offset */

		int nops;			/* number of nops */

	} insn[DISAS_ALT_INSN_MAX];		/* alternative instructions */

	int insn_idx;				/* index of the next instruction to print */

};
@@ -727,7 +728,7 @@ static int disas_alt_init(struct disas_alt *dalt, 
}



static int disas_alt_add_insn(struct disas_alt *dalt, int index, char *insn_str,

			      int offset)

			      int offset, int nops)

{

	int len;
@@ -740,6 +741,7 @@ static int disas_alt_add_insn(struct disas_alt *dalt, int index, char *insn_str, 
	len = strlen(insn_str);

	dalt->insn[index].str = insn_str;

	dalt->insn[index].offset = offset;

	dalt->insn[index].nops = nops;

	if (len > dalt->width)

		dalt->width = len;
@@ -752,6 +754,7 @@ static int disas_alt_jump(struct disas_alt *dalt) 
	struct instruction *dest_insn;

	char suffix[2] = { 0 };

	char *str;

	int nops;



	orig_insn = dalt->orig_insn;

	dest_insn = dalt->alt->insn;
@@ -762,14 +765,16 @@ static int disas_alt_jump(struct disas_alt *dalt) 
		str = strfmt("jmp%-3s %lx <%s+0x%lx>", suffix,

			     dest_insn->offset, dest_insn->sym->name,

			     dest_insn->offset - dest_insn->sym->offset);

		nops = 0;

	} else {

		str = strfmt("nop%d", orig_insn->len);

		nops = orig_insn->len;

	}



	if (!str)

		return -1;



	disas_alt_add_insn(dalt, 0, str, 0);

	disas_alt_add_insn(dalt, 0, str, 0, nops);



	return 1;

}
@@ -789,7 +794,7 @@ static int disas_alt_extable(struct disas_alt *dalt) 
	if (!str)

		return -1;



	disas_alt_add_insn(dalt, 0, str, 0);

	disas_alt_add_insn(dalt, 0, str, 0, 0);



	return 1;

}
@@ -805,11 +810,13 @@ static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt) 
	int offset;

	char *str;

	int count;

	int nops;

	int err;



	file = dctx->file;

	count = 0;

	offset = 0;

	nops = 0;



	alt_for_each_insn(file, DALT_GROUP(dalt), insn) {
@@ -818,7 +825,8 @@ static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt) 
		if (!str)

			return -1;



		err = disas_alt_add_insn(dalt, count, str, offset);

		nops = insn->type == INSN_NOP ? insn->len : 0;

		err = disas_alt_add_insn(dalt, count, str, offset, nops);

		if (err)

			break;

		offset += insn->len;
@@ -834,6 +842,7 @@ static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt) 
static int disas_alt_default(struct disas_context *dctx, struct disas_alt *dalt)

{

	char *str;

	int nops;

	int err;



	if (DALT_GROUP(dalt))
@@ -849,7 +858,8 @@ static int disas_alt_default(struct disas_context *dctx, struct disas_alt *dalt) 
	str = strdup(disas_result(dctx));

	if (!str)

		return -1;

	err = disas_alt_add_insn(dalt, 0, str, 0);

	nops = dalt->orig_insn->type == INSN_NOP ? dalt->orig_insn->len : 0;

	err = disas_alt_add_insn(dalt, 0, str, 0, nops);

	if (err)

		return -1;
@@ -995,6 +1005,62 @@ static void disas_alt_print_compact(char *alt_name, struct disas_alt *dalts, 
	}

}



/*

 * Trim NOPs in alternatives. This replaces trailing NOPs in alternatives

 * with a single indication of the number of bytes covered with NOPs.

 *

 * Return the maximum numbers of instructions in all alternatives after

 * trailing NOPs have been trimmed.

 */

static int disas_alt_trim_nops(struct disas_alt *dalts, int alt_count,

			       int insn_count)

{

	struct disas_alt *dalt;

	int nops_count;

	const char *s;

	int offset;

	int count;

	int nops;

	int i, j;



	count = 0;

	for (i = 0; i < alt_count; i++) {

		offset = 0;

		nops = 0;

		nops_count = 0;

		dalt = &dalts[i];

		for (j = insn_count - 1; j >= 0; j--) {

			if (!dalt->insn[j].str || !dalt->insn[j].nops)

				break;

			offset = dalt->insn[j].offset;

			free(dalt->insn[j].str);

			dalt->insn[j].offset = 0;

			dalt->insn[j].str = NULL;

			nops += dalt->insn[j].nops;

			nops_count++;

		}



		/*

		 * All trailing NOPs have been removed. If there was a single

		 * NOP instruction then re-add it. If there was a block of

		 * NOPs then indicate the number of bytes than the block

		 * covers (nop*<number-of-bytes>).

		 */

		if (nops_count) {

			s = nops_count == 1 ? "" : "*";

			dalt->insn[j + 1].str = strfmt("nop%s%d", s, nops);

			dalt->insn[j + 1].offset = offset;

			dalt->insn[j + 1].nops = nops;

			j++;

		}



		if (j > count)

			count = j;

	}



	return count + 1;

}



/*

 * Disassemble an alternative.

 *
@@ -1083,6 +1149,8 @@ static void *disas_alt(struct disas_context *dctx, 
	 * Print default and non-default alternatives.

	 */



	insn_count = disas_alt_trim_nops(dalts, alt_count, insn_count);



	if (opts.wide)

		disas_alt_print_wide(alt_name, dalts, alt_count, insn_count);

	else