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Fix SIGFPE at startup when CPUID leaf 0x15 is unusable with tpause #43

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Merged
byrnedj merged 1 commit into from
Oct 27, 2026
Merged

Fix SIGFPE at startup when CPUID leaf 0x15 is unusable with tpause #43

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63 changes: 39 additions & 24 deletions dto.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1255,10 +1255,10 @@ static int dsa_init(void)
const char *env_str;
char wq_list[256];

/* detect waitpkg support */
leaf = 7;
/* detect waitpkg support: CPUID.(EAX=7,ECX=0):ECX bit 5 */
leaf = 0;
waitpkg = 0;
if (__get_cpuid(0, &leaf, unused, &waitpkg, unused + 1)) {
if (__get_cpuid_count(7, 0, &leaf, unused, &waitpkg, unused + 1)) {
if (waitpkg & 0x20) {
LOG_TRACE("waitpkg supported\n");
waitpkg_support = 1;
Expand Down Expand Up @@ -1539,27 +1539,42 @@ static int init_dto(void)
use_std_lib_calls = 1;
}

// calculate the wait time for TPAUSE
if (wait_method == WAIT_TPAUSE) {
unsigned int num, den, freq;
unsigned int empty;
unsigned long long tmp;
__get_cpuid( 0x15, &den, &num, &freq, &empty );
freq /= 1000;
LOG_TRACE( "Core Freq = %u kHz\n", freq );
LOG_TRACE( "TSC Mult = %u\n", num );
LOG_TRACE( "TSC Den = %u\n", den );
freq *= num;
freq /= den;
LOG_TRACE( "CPU freq = %u kHz\n", freq );

LOG_TRACE( "Requested wait: %llu nsec\n", tpause_wait_time );
tmp = tpause_wait_time;
tmp *= freq;
tpause_wait_time = tmp / NSEC_PER_MSEC;
LOG_TRACE( "Requested wait duration: %llu cycles\n", tpause_wait_time );
}

/*
* Calculate the wait time for TPAUSE. This converts ns to TSC
* cycles using CPUID leaf 0x15, which may be absent or report a
* zero denominator/crystal frequency (common in VMs and on
* older parts), so verify it before dividing.
*/
if (!use_std_lib_calls && wait_method == WAIT_TPAUSE) {
unsigned int num = 0, den = 0, freq = 0;
unsigned int empty;
unsigned long long tmp;

if (!__get_cpuid(0x15, &den, &num, &freq, &empty) ||
den == 0 || num == 0 || freq == 0) {
LOG_ERROR("CPUID leaf 0x15 unavailable (den=%u, num=%u, freq=%u); "
"cannot compute TSC frequency for tpause. Falling back to busypoll\n",
den, num, freq);
wait_method = WAIT_BUSYPOLL;
min_avg_waits = MIN_AVG_POLL_WAITS;
max_avg_waits = MAX_AVG_POLL_WAITS;
} else {
freq /= 1000;
LOG_TRACE("Core Freq = %u kHz\n", freq);
LOG_TRACE("TSC Mult = %u\n", num);
LOG_TRACE("TSC Den = %u\n", den);
freq *= num;
freq /= den;
LOG_TRACE("CPU freq = %u kHz\n", freq);

LOG_TRACE("Requested wait: %llu nsec\n", tpause_wait_time);
tmp = tpause_wait_time;
tmp *= freq;
tpause_wait_time = tmp / NSEC_PER_MSEC;
LOG_TRACE("Requested wait duration: %llu cycles\n", tpause_wait_time);
}
}

// display configuration
LOG_TRACE("log_level: %d, collect_stats: %d, use_std_lib_calls: %d, dsa_min_size: %lu, "
"cpu_size_fraction: %.2f, wait_method: %s, auto_adjust_knobs: %d, numa_awareness: %s, dto_dsa_cc: %d\n",
Expand Down
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