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Message-ID: <20251119143247.3944213-31-alexandre.chartre@oracle.com>
Date: Wed, 19 Nov 2025 15:32:47 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: linux-kernel@...r.kernel.org, mingo@...nel.org, jpoimboe@...nel.org,
peterz@...radead.org, david.laight.linux@...il.com
Cc: alexandre.chartre@...cle.com
Subject: [PATCH v5 30/30] 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@...cle.com>
---
tools/objtool/disas.c | 78 ++++++++++++++++++++++++++++++++++++++++---
1 file changed, 73 insertions(+), 5 deletions(-)
diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
index f04bc14bef39e..441b9306eafcc 100644
--- a/tools/objtool/disas.c
+++ b/tools/objtool/disas.c
@@ -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
--
2.43.5
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