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Message-ID: <20251113164917.2563486-28-alexandre.chartre@oracle.com>
Date: Thu, 13 Nov 2025 17:49:16 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: linux-kernel@...r.kernel.org, mingo@...nel.org, jpoimboe@...nel.org,
peterz@...radead.org
Cc: alexandre.chartre@...cle.com
Subject: [PATCH v4 27/28] objtool: Improve the disassembly of the pv_ops call
When using the --disas option, print the destination name of pv_ops
calls when we can figure out if XENPV mode is used or not. If the
PV mode can't be predicted when print the default pv_ops destination
as a destination example.
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
tools/objtool/disas.c | 101 +++++++++++++++++++++++++++++++++++++-----
1 file changed, 89 insertions(+), 12 deletions(-)
diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
index 2a6c3708ec315..20d64b58182ce 100644
--- a/tools/objtool/disas.c
+++ b/tools/objtool/disas.c
@@ -12,6 +12,7 @@
#include <objtool/special.h>
#include <objtool/warn.h>
+#include <asm/cpufeatures.h>
#include <bfd.h>
#include <linux/string.h>
#include <tools/dis-asm-compat.h>
@@ -54,6 +55,7 @@ struct disas_alt {
int offset; /* instruction offset */
} insn[DISAS_ALT_INSN_MAX]; /* alternative instructions */
int insn_idx; /* index of the next instruction to print */
+ int pv_mode; /* PV mode */
};
#define DALT_DEFAULT(dalt) (!(dalt)->alt)
@@ -665,13 +667,65 @@ char *disas_alt_name(struct alternative *alt)
return str;
}
+/*
+ * Set the PV mode for the current alternative and return the PV mode
+ * to use for next alternatives.
+ */
+static enum pv_mode disas_alt_set_pvmode(struct disas_alt *dalt,
+ enum pv_mode pv_mode)
+{
+ struct alt_group *alt_group;
+ int feature;
+ int flags;
+
+ dalt->pv_mode = pv_mode;
+
+ alt_group = DALT_GROUP(dalt);
+ if (!alt_group)
+ return pv_mode;
+
+ feature = alt_feature(alt_group->feature);
+ flags = alt_flags(alt_group->feature);
+
+ /*
+ * The only PV mode we identify is the XENPV mode which is
+ * enabled with the X86_FEATURE_XENPV feature. When we are
+ * sure that XENPV mode is not used then assume that the
+ * default PV mode is used.
+ */
+ if (feature != X86_FEATURE_XENPV)
+ return pv_mode;
+
+ if (flags & ALT_FLAG_NOT) {
+ /*
+ * This alternative is not used with XENPV mode, so
+ * it is used in default mode. Then next alternatives
+ * will be used in XENPV mode.
+ */
+ dalt->pv_mode = PV_MODE_DEFAULT;
+ pv_mode = PV_MODE_XENPV;
+ } else {
+ /*
+ * This alternative is used with XENPV mode so next
+ * alternatives will apply in default mode.
+ */
+ dalt->pv_mode = PV_MODE_XENPV;
+ pv_mode = PV_MODE_DEFAULT;
+ }
+
+ return pv_mode;
+}
+
/*
* Initialize an alternative. The default alternative should be initialized
* with alt=NULL.
+ *
+ * Return the PV mode to use for the next alternative or -1 on error.
*/
-static int disas_alt_init(struct disas_alt *dalt,
- struct instruction *orig_insn,
- struct alternative *alt)
+static enum pv_mode disas_alt_init(struct disas_alt *dalt,
+ struct instruction *orig_insn,
+ struct alternative *alt,
+ enum pv_mode pv_mode)
{
dalt->orig_insn = orig_insn;
dalt->alt = alt;
@@ -682,7 +736,7 @@ static int disas_alt_init(struct disas_alt *dalt,
return -1;
dalt->width = strlen(dalt->name);
- return 0;
+ return disas_alt_set_pvmode(dalt, pv_mode);
}
static int disas_alt_add_insn(struct disas_alt *dalt, int index, char *insn_str,
@@ -753,27 +807,50 @@ static int disas_alt_extable(struct disas_alt *dalt)
return 1;
}
+static bool disas_alt_is_direct_call(struct instruction *insn)
+{
+ return (insn->alt_group &&
+ (alt_flags(insn->alt_group->feature) & ALT_FLAG_DIRECT_CALL));
+}
+
/*
* Disassemble an alternative and store instructions in the disas_alt
* structure. Return the number of instructions in the alternative.
*/
static int disas_alt_group(struct disas_context *dctx, struct disas_alt *dalt)
{
+ struct instruction *orig_insn;
struct objtool_file *file;
struct instruction *insn;
+ const char *name;
int offset;
char *str;
int count;
int err;
file = dctx->file;
+ orig_insn = dalt->orig_insn;
count = 0;
offset = 0;
alt_for_each_insn(file, DALT_GROUP(dalt), insn) {
-
- disas_insn_alt(dctx, insn);
- str = strdup(disas_result(dctx));
+ /*
+ * An alternative direct call initially has the
+ * "call BUG_func" instruction but it will be
+ * replaced with a direct call to the target of
+ * the pv_ops call in the original instruction.
+ */
+ if (disas_alt_is_direct_call(insn)) {
+ name = pv_call_dest_name(file, orig_insn,
+ dalt->pv_mode);
+ if (name)
+ str = strfmt("callq %s", name);
+ else
+ str = strdup("NOP");
+ } else {
+ disas_insn_alt(dctx, insn);
+ str = strdup(disas_result(dctx));
+ }
if (!str)
return -1;
@@ -876,6 +953,7 @@ static void *disas_alt(struct disas_context *dctx,
struct instruction *orig_insn)
{
struct disas_alt alts[DISAS_ALT_MAX] = { 0 };
+ enum pv_mode pv_mode = PV_MODE_UNKNOWN;
struct alternative *alt;
struct disas_alt *dalt;
int offset_next;
@@ -884,7 +962,6 @@ static void *disas_alt(struct disas_context *dctx,
int alt_id;
int offset;
int count;
- int err;
int i;
alt_id = orig_insn->offset;
@@ -892,8 +969,8 @@ static void *disas_alt(struct disas_context *dctx,
/*
* Initialize and disassemble the default alternative.
*/
- err = disas_alt_init(&alts[0], orig_insn, NULL);
- if (err)
+ pv_mode = disas_alt_init(&alts[0], orig_insn, NULL, pv_mode);
+ if (pv_mode < 0)
goto error;
insn_count = disas_alt_default(dctx, &alts[0]);
@@ -911,8 +988,8 @@ static void *disas_alt(struct disas_context *dctx,
break;
}
dalt = &alts[i];
- err = disas_alt_init(dalt, orig_insn, alt);
- if (err)
+ pv_mode = disas_alt_init(dalt, orig_insn, alt, pv_mode);
+ if (pv_mode < 0)
goto error;
count = -1;
--
2.43.5
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