which contains "1" if the feature is supported and
"0" otherwise.
+ As an alternative, refer to "Emulated PTWRITE" further below.
+
fup_on_ptw Enable a FUP packet to follow the PTWRITE packet. The FUP packet
provides the address of the ptwrite instruction. In the absence of
fup_on_ptw, the decoder will use the address of the previous branch
to reconstruct the control flow is not possible.
+Emulated PTWRITE
+----------------
+
+Later perf tools support a method to emulate the ptwrite instruction, which
+can be useful if hardware does not support the ptwrite instruction.
+
+Instead of using the ptwrite instruction, a function is used which produces
+a trace that encodes the payload data into TNT packets. Here is an example
+of the function:
+
+ #include <stdint.h>
+
+ void perf_emulate_ptwrite(uint64_t x)
+ __attribute__((externally_visible, noipa, no_instrument_function, naked));
+
+ #define PERF_EMULATE_PTWRITE_8_BITS \
+ "1: shl %rax\n" \
+ " jc 1f\n" \
+ "1: shl %rax\n" \
+ " jc 1f\n" \
+ "1: shl %rax\n" \
+ " jc 1f\n" \
+ "1: shl %rax\n" \
+ " jc 1f\n" \
+ "1: shl %rax\n" \
+ " jc 1f\n" \
+ "1: shl %rax\n" \
+ " jc 1f\n" \
+ "1: shl %rax\n" \
+ " jc 1f\n" \
+ "1: shl %rax\n" \
+ " jc 1f\n"
+
+ /* Undefined instruction */
+ #define PERF_EMULATE_PTWRITE_UD2 ".byte 0x0f, 0x0b\n"
+
+ #define PERF_EMULATE_PTWRITE_MAGIC PERF_EMULATE_PTWRITE_UD2 ".ascii \"perf,ptwrite \"\n"
+
+ void perf_emulate_ptwrite(uint64_t x __attribute__ ((__unused__)))
+ {
+ /* Assumes SysV ABI : x passed in rdi */
+ __asm__ volatile (
+ "jmp 1f\n"
+ PERF_EMULATE_PTWRITE_MAGIC
+ "1: mov %rdi, %rax\n"
+ PERF_EMULATE_PTWRITE_8_BITS
+ PERF_EMULATE_PTWRITE_8_BITS
+ PERF_EMULATE_PTWRITE_8_BITS
+ PERF_EMULATE_PTWRITE_8_BITS
+ PERF_EMULATE_PTWRITE_8_BITS
+ PERF_EMULATE_PTWRITE_8_BITS
+ PERF_EMULATE_PTWRITE_8_BITS
+ PERF_EMULATE_PTWRITE_8_BITS
+ "1: ret\n"
+ );
+ }
+
+For example, a test program with the function above:
+
+ #include <stdio.h>
+ #include <stdint.h>
+ #include <stdlib.h>
+
+ #include "perf_emulate_ptwrite.h"
+
+ int main(int argc, char *argv[])
+ {
+ uint64_t x = 0;
+
+ if (argc > 1)
+ x = strtoull(argv[1], NULL, 0);
+ perf_emulate_ptwrite(x);
+ return 0;
+ }
+
+Can be compiled and traced:
+
+ $ gcc -Wall -Wextra -O3 -g -o eg_ptw eg_ptw.c
+ $ perf record -e intel_pt//u ./eg_ptw 0x1234567890abcdef
+ [ perf record: Woken up 1 times to write data ]
+ [ perf record: Captured and wrote 0.017 MB perf.data ]
+ $ perf script --itrace=ew
+ eg_ptw 19875 [007] 8061.235912: ptwrite: IP: 0 payload: 0x1234567890abcdef 55701249a196 perf_emulate_ptwrite+0x16 (/home/user/eg_ptw)
+ $
+
+
EXAMPLE
-------
bool in_psb;
bool hop;
bool leap;
+ bool emulated_ptwrite;
bool vm_time_correlation;
bool vm_tm_corr_dry_run;
bool vm_tm_corr_reliable;
return INTEL_PT_ERR_LOST;
case -ELOOP:
return INTEL_PT_ERR_NELOOP;
+ case -ECONNRESET:
+ return INTEL_PT_ERR_EPTW;
default:
return INTEL_PT_ERR_UNK;
}
[INTEL_PT_ERR_LOST] = "Lost trace data",
[INTEL_PT_ERR_UNK] = "Unknown error!",
[INTEL_PT_ERR_NELOOP] = "Never-ending loop (refer perf config intel-pt.max-loops)",
+ [INTEL_PT_ERR_EPTW] = "Broken emulated ptwrite",
};
int intel_pt__strerror(int code, char *buf, size_t buflen)
return intel_pt_bug(decoder);
}
+struct eptw_data {
+ int bit_countdown;
+ uint64_t payload;
+};
+
+static int intel_pt_eptw_lookahead_cb(struct intel_pt_pkt_info *pkt_info)
+{
+ struct eptw_data *data = pkt_info->data;
+ int nr_bits;
+
+ switch (pkt_info->packet.type) {
+ case INTEL_PT_PAD:
+ case INTEL_PT_MNT:
+ case INTEL_PT_MODE_EXEC:
+ case INTEL_PT_MODE_TSX:
+ case INTEL_PT_MTC:
+ case INTEL_PT_FUP:
+ case INTEL_PT_CYC:
+ case INTEL_PT_CBR:
+ case INTEL_PT_TSC:
+ case INTEL_PT_TMA:
+ case INTEL_PT_PIP:
+ case INTEL_PT_VMCS:
+ case INTEL_PT_PSB:
+ case INTEL_PT_PSBEND:
+ case INTEL_PT_PTWRITE:
+ case INTEL_PT_PTWRITE_IP:
+ case INTEL_PT_EXSTOP:
+ case INTEL_PT_EXSTOP_IP:
+ case INTEL_PT_MWAIT:
+ case INTEL_PT_PWRE:
+ case INTEL_PT_PWRX:
+ case INTEL_PT_BBP:
+ case INTEL_PT_BIP:
+ case INTEL_PT_BEP:
+ case INTEL_PT_BEP_IP:
+ case INTEL_PT_CFE:
+ case INTEL_PT_CFE_IP:
+ case INTEL_PT_EVD:
+ break;
+
+ case INTEL_PT_TNT:
+ nr_bits = data->bit_countdown;
+ if (nr_bits > pkt_info->packet.count)
+ nr_bits = pkt_info->packet.count;
+ data->payload <<= nr_bits;
+ data->payload |= pkt_info->packet.payload >> (64 - nr_bits);
+ data->bit_countdown -= nr_bits;
+ return !data->bit_countdown;
+
+ case INTEL_PT_TIP_PGE:
+ case INTEL_PT_TIP_PGD:
+ case INTEL_PT_TIP:
+ case INTEL_PT_BAD:
+ case INTEL_PT_OVF:
+ case INTEL_PT_TRACESTOP:
+ default:
+ return 1;
+ }
+
+ return 0;
+}
+
+static int intel_pt_emulated_ptwrite(struct intel_pt_decoder *decoder)
+{
+ int n = 64 - decoder->tnt.count;
+ struct eptw_data data = {
+ .bit_countdown = n,
+ .payload = decoder->tnt.payload >> n,
+ };
+
+ decoder->emulated_ptwrite = false;
+ intel_pt_log("Emulated ptwrite detected\n");
+
+ intel_pt_pkt_lookahead(decoder, intel_pt_eptw_lookahead_cb, &data);
+ if (data.bit_countdown)
+ return -ECONNRESET;
+
+ decoder->state.type = INTEL_PT_PTW;
+ decoder->state.from_ip = decoder->ip;
+ decoder->state.to_ip = 0;
+ decoder->state.ptw_payload = data.payload;
+ return 0;
+}
+
static int intel_pt_walk_tnt(struct intel_pt_decoder *decoder)
{
struct intel_pt_insn intel_pt_insn;
int err;
while (1) {
+ if (decoder->emulated_ptwrite)
+ return intel_pt_emulated_ptwrite(decoder);
err = intel_pt_walk_insn(decoder, &intel_pt_insn, 0);
- if (err == INTEL_PT_RETURN)
+ if (err == INTEL_PT_RETURN) {
+ decoder->emulated_ptwrite = intel_pt_insn.emulated_ptwrite;
return 0;
- if (err)
+ }
+ if (err) {
+ decoder->emulated_ptwrite = false;
return err;
+ }
if (intel_pt_insn.op == INTEL_PT_OP_RET) {
if (!decoder->return_compression) {
INTEL_PT_ERR_LOST,
INTEL_PT_ERR_UNK,
INTEL_PT_ERR_NELOOP,
+ INTEL_PT_ERR_EPTW,
INTEL_PT_ERR_MAX,
};
int ext;
intel_pt_insn->rel = 0;
+ intel_pt_insn->emulated_ptwrite = false;
if (insn_is_avx(insn)) {
intel_pt_insn->op = INTEL_PT_OP_OTHER;
struct intel_pt_insn {
enum intel_pt_insn_op op;
enum intel_pt_insn_branch branch;
+ bool emulated_ptwrite;
int length;
int32_t rel;
unsigned char buf[INTEL_PT_INSN_BUF_SZ];
u64 byte_cnt;
enum intel_pt_insn_op op;
enum intel_pt_insn_branch branch;
+ bool emulated_ptwrite;
int length;
int32_t rel;
char insn[INTEL_PT_INSN_BUF_SZ];
e->byte_cnt = byte_cnt;
e->op = intel_pt_insn->op;
e->branch = intel_pt_insn->branch;
+ e->emulated_ptwrite = intel_pt_insn->emulated_ptwrite;
e->length = intel_pt_insn->length;
e->rel = intel_pt_insn->rel;
memcpy(e->insn, intel_pt_insn->buf, INTEL_PT_INSN_BUF_SZ);
return 0;
}
+static inline bool intel_pt_jmp_16(struct intel_pt_insn *intel_pt_insn)
+{
+ return intel_pt_insn->rel == 16 && intel_pt_insn->branch == INTEL_PT_BR_UNCONDITIONAL;
+}
+
+#define PTWRITE_MAGIC "\x0f\x0bperf,ptwrite "
+#define PTWRITE_MAGIC_LEN 16
+
+static bool intel_pt_emulated_ptwrite(struct dso *dso, struct machine *machine, u64 offset)
+{
+ unsigned char buf[PTWRITE_MAGIC_LEN];
+ ssize_t len;
+
+ len = dso__data_read_offset(dso, machine, offset, buf, PTWRITE_MAGIC_LEN);
+ if (len == PTWRITE_MAGIC_LEN && !memcmp(buf, PTWRITE_MAGIC, PTWRITE_MAGIC_LEN)) {
+ intel_pt_log("Emulated ptwrite signature found\n");
+ return true;
+ }
+ intel_pt_log("Emulated ptwrite signature not found\n");
+ return false;
+}
+
static int intel_pt_walk_next_insn(struct intel_pt_insn *intel_pt_insn,
uint64_t *insn_cnt_ptr, uint64_t *ip,
uint64_t to_ip, uint64_t max_insn_cnt,
*ip += e->byte_cnt;
intel_pt_insn->op = e->op;
intel_pt_insn->branch = e->branch;
+ intel_pt_insn->emulated_ptwrite = e->emulated_ptwrite;
intel_pt_insn->length = e->length;
intel_pt_insn->rel = e->rel;
memcpy(intel_pt_insn->buf, e->insn,
insn_cnt += 1;
- if (intel_pt_insn->branch != INTEL_PT_BR_NO_BRANCH)
+ if (intel_pt_insn->branch != INTEL_PT_BR_NO_BRANCH) {
+ bool eptw;
+ u64 offs;
+
+ if (!intel_pt_jmp_16(intel_pt_insn))
+ goto out;
+ /* Check for emulated ptwrite */
+ offs = offset + intel_pt_insn->length;
+ eptw = intel_pt_emulated_ptwrite(al.map->dso, machine, offs);
+ intel_pt_insn->emulated_ptwrite = eptw;
goto out;
+ }
if (max_insn_cnt && insn_cnt >= max_insn_cnt)
goto out_no_cache;
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