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x86: Add generic CPUID data dumper to ld.so --list-diagnostics

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This is surprisingly difficult to implement if the goal is to produce
reasonably sized output.  With the current approaches to output
compression (suppressing zeros and repeated results between CPUs,
folding ranges of identical subleaves, dealing with the %ecx
reflection issue), the output is less than 600 KiB even for systems
with 256 logical CPUs.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
This commit is contained in:
Florian Weimer 2024-04-08 16:48:55 +02:00
parent 5653ccd847
commit 7a430f40c4
2 changed files with 468 additions and 1 deletions
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85
manual/dynlink.texi
View File

@ -228,7 +228,90 @@ reported by the @code{uname} function. @xref{Platform Type}.
@item x86.cpu_features.@dots{}
These items are specific to the i386 and x86-64 architectures. They
reflect supported CPU features and information on cache geometry, mostly
collected using the @code{CPUID} instruction.
collected using the CPUID instruction.
@item x86.processor[@var{index}].@dots{}
These are additional items for the i386 and x86-64 architectures, as
described below. They mostly contain raw data from the CPUID
instruction. The probes are performed for each active CPU for the
@code{ld.so} process, and data for different probed CPUs receives a
uniqe @var{index} value. Some CPUID data is expected to differ from CPU
core to CPU core. In some cases, CPUs are not correctly initialized and
indicate the presence of different feature sets.
@item x86.processor[@var{index}].requested=@var{kernel-cpu}
The kernel is told to run the subsequent probing on the CPU numbered
@var{kernel-cpu}. The values @var{kernel-cpu} and @var{index} can be
distinct if there are gaps in the process CPU affinity mask. This line
is not included if CPU affinity mask information is not available.
@item x86.processor[@var{index}].observed=@var{kernel-cpu}
This line reports the kernel CPU number @var{kernel-cpu} on which the
probing code initially ran. If the CPU number cannot be obtained,
this line is not printed.
@item x86.processor[@var{index}].observed_node=@var{node}
This reports the observed NUMA node number, as reported by the
@code{getcpu} system call. If this information cannot be obtained, this
line is not printed.
@item x86.processor[@var{index}].cpuid_leaves=@var{count}
This line indicates that @var{count} distinct CPUID leaves were
encountered. (This reflects internal @code{ld.so} storage space, it
does not directly correspond to @code{CPUID} enumeration ranges.)
@item x86.processor[@var{index}].ecx_limit=@var{value}
The CPUID data extraction code uses a brute-force approach to enumerate
subleaves (see the @samp{.subleaf_eax} lines below). The last
@code{%rcx} value used in a CPUID query on this probed CPU was
@var{value}.
@item x86.processor[@var{index}].cpuid.eax[@var{query_eax}].eax=@var{eax}
@itemx x86.processor[@var{index}].cpuid.eax[@var{query_eax}].ebx=@var{ebx}
@itemx x86.processor[@var{index}].cpuid.eax[@var{query_eax}].ecx=@var{ecx}
@itemx x86.processor[@var{index}].cpuid.eax[@var{query_eax}].edx=@var{edx}
These lines report the register contents after executing the CPUID
instruction with @samp{%rax == @var{query_eax}} and @samp{%rcx == 0} (a
@dfn{leaf}). For the first probed CPU (with a zero @var{index}), only
leaves with non-zero register contents are reported. For subsequent
CPUs, only leaves whose register contents differs from the previously
probed CPUs (with @var{index} one less) are reported.
Basic and extended leaves are reported using the same syntax. This
means there is a large jump in @var{query_eax} for the first reported
extended leaf.
@item x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].eax=@var{eax}
@itemx x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].ebx=@var{ebx}
@itemx x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].ecx=@var{ecx}
@itemx x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].edx=@var{edx}
This is similar to the leaves above, but for a @dfn{subleaf}. For
subleaves, the CPUID instruction is executed with @samp{%rax ==
@var{query_eax}} and @samp{%rcx == @var{query_ecx}}, so the result
depends on both register values. The same rules about filtering zero
and identical results apply.
@item x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].until_ecx=@var{ecx_limit}
Some CPUID results are the same regardless the @var{query_ecx} value.
If this situation is detected, a line with the @samp{.until_ecx}
selector ins included, and this indicates that the CPUID register
contents is the same for @code{%rcx} values between @var{query_ecx}
and @var{ecx_limit} (inclusive).
@item x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].ecx_query_mask=0xff
This line indicates that in an @samp{.until_ecx} range, the CPUID
instruction preserved the lowested 8 bits of the input @code{%rcx} in
the output @code{%rcx} registers. Otherwise, the subleaves in the range
have identical values. This special treatment is necessary to report
compact range information in case such copying occurs (because the
subleaves would otherwise be all different).
@item x86.processor[@var{index}].xgetbv.ecx[@var{query_ecx}]=@var{result}
This line shows the 64-bit @var{result} value in the @code{%rdx:%rax}
register pair after executing the XGETBV instruction with @code{%rcx}
set to @var{query_ecx}. Zero values and values matching the previously
probed CPU are omitted. Nothing is printed if the system does not
support the XGETBV instruction.
@end table
@node Dynamic Linker Introspection

384
sysdeps/x86/dl-diagnostics-cpu.c
View File

@ -17,7 +17,18 @@
<https://www.gnu.org/licenses/>. */
#include <dl-diagnostics.h>
#include <array_length.h>
#include <cpu-features.h>
#include <cpuid.h>
#include <dl-iterate_cpu.h>
#include <ldsodefs.h>
#include <stdbool.h>
#include <string.h>
#include <sysdep.h>
/* The generic CPUID dumping code. */
static void _dl_diagnostics_cpuid (void);
static void
print_cpu_features_value (const char *label, uint64_t value)
@ -120,4 +131,377 @@ _dl_diagnostics_cpu (void)
+ sizeof (cpu_features->cachesize_non_temporal_divisor)
== sizeof (*cpu_features),
"last cpu_features field has been printed");
_dl_diagnostics_cpuid ();
}
/* The following code implements a generic CPUID dumper that tries to
gather CPUID data without knowing about CPUID implementation
details. */
/* Register arguments to CPUID. Multiple ECX subleaf values yielding
the same result are combined, to shorten the output. Both
identical matches (EAX to EDX are the same) and matches where EAX,
EBX, EDX, and ECX are equal except in the lower byte, which must
match the query ECX value. The latter is needed to compress ranges
on CPUs which preserve the lowest byte in ECX if an unknown leaf is
queried. */
struct cpuid_query
{
unsigned int eax;
unsigned ecx_first;
unsigned ecx_last;
bool ecx_preserves_query_byte;
};
/* Single integer value that can be used for sorting/ordering
comparisons. Uses Q->eax and Q->ecx_first only because ecx_last is
always greater than the previous ecx_first value and less than the
subsequent one. */
static inline unsigned long long int
cpuid_query_combined (struct cpuid_query *q)
{
/* ecx can be -1 (that is, ~0U). If this happens, this the only ecx
value for this eax value, so the ordering does not matter. */
return ((unsigned long long int) q->eax << 32) | (unsigned int) q->ecx_first;
};
/* Used for differential reporting of zero/non-zero values. */
static const struct cpuid_registers cpuid_registers_zero;
/* Register arguments to CPUID paired with the results that came back. */
struct cpuid_query_result
{
struct cpuid_query q;
struct cpuid_registers r;
};
/* During a first enumeration pass, we try to collect data for
cpuid_initial_subleaf_limit subleaves per leaf/EAX value. If we run
out of space, we try once more with applying the lower limit. */
enum { cpuid_main_leaf_limit = 128 };
enum { cpuid_initial_subleaf_limit = 512 };
enum { cpuid_subleaf_limit = 32 };
/* Offset of the extended leaf area. */
enum {cpuid_extended_leaf_offset = 0x80000000 };
/* Collected CPUID data. Everything is stored in a statically sized
array that is sized so that the second pass will collect some data
for all leaves, after the limit is applied. On the second pass,
ecx_limit is set to cpuid_subleaf_limit. */
struct cpuid_collected_data
{
unsigned int used;
unsigned int ecx_limit;
uint64_t xgetbv_ecx_0;
struct cpuid_query_result qr[cpuid_main_leaf_limit
* 2 * cpuid_subleaf_limit];
};
/* Fill in the result of a CPUID query. Returns true if there is
room, false if nothing could be stored. */
static bool
_dl_diagnostics_cpuid_store (struct cpuid_collected_data *ccd,
unsigned eax, int ecx)
{
if (ccd->used >= array_length (ccd->qr))
return false;
/* Tentatively fill in the next value. */
__cpuid_count (eax, ecx,
ccd->qr[ccd->used].r.eax,
ccd->qr[ccd->used].r.ebx,
ccd->qr[ccd->used].r.ecx,
ccd->qr[ccd->used].r.edx);
/* If the ECX subleaf is next subleaf after the previous one (for
the same leaf), and the values are the same, merge the result
with the already-stored one. Do this before skipping zero
leaves, which avoids artifiacts for ECX == 256 queries. */
if (ccd->used > 0
&& ccd->qr[ccd->used - 1].q.eax == eax
&& ccd->qr[ccd->used - 1].q.ecx_last + 1 == ecx)
{
/* Exact match of the previous result. Ignore the value of
ecx_preserves_query_byte if this is a singleton range so far
because we can treat ECX as fixed if the same value repeats. */
if ((!ccd->qr[ccd->used - 1].q.ecx_preserves_query_byte
|| (ccd->qr[ccd->used - 1].q.ecx_first
== ccd->qr[ccd->used - 1].q.ecx_last))
&& memcmp (&ccd->qr[ccd->used - 1].r, &ccd->qr[ccd->used].r,
sizeof (ccd->qr[ccd->used].r)) == 0)
{
ccd->qr[ccd->used - 1].q.ecx_last = ecx;
/* ECX is now fixed because the same value has been observed
twice, even if we had a low-byte match before. */
ccd->qr[ccd->used - 1].q.ecx_preserves_query_byte = false;
return true;
}
/* Match except for the low byte in ECX, which must match the
incoming ECX value. */
if (ccd->qr[ccd->used - 1].q.ecx_preserves_query_byte
&& (ecx & 0xff) == (ccd->qr[ccd->used].r.ecx & 0xff)
&& ccd->qr[ccd->used].r.eax == ccd->qr[ccd->used - 1].r.eax
&& ccd->qr[ccd->used].r.ebx == ccd->qr[ccd->used - 1].r.ebx
&& ((ccd->qr[ccd->used].r.ecx & 0xffffff00)
== (ccd->qr[ccd->used - 1].r.ecx & 0xffffff00))
&& ccd->qr[ccd->used].r.edx == ccd->qr[ccd->used - 1].r.edx)
{
ccd->qr[ccd->used - 1].q.ecx_last = ecx;
return true;
}
}
/* Do not store zero results. All-zero values usually mean that the
subleaf is unsupported. */
if (ccd->qr[ccd->used].r.eax == 0
&& ccd->qr[ccd->used].r.ebx == 0
&& ccd->qr[ccd->used].r.ecx == 0
&& ccd->qr[ccd->used].r.edx == 0)
return true;
/* The result needs to be stored. Fill in the query parameters and
consume the storage. */
ccd->qr[ccd->used].q.eax = eax;
ccd->qr[ccd->used].q.ecx_first = ecx;
ccd->qr[ccd->used].q.ecx_last = ecx;
ccd->qr[ccd->used].q.ecx_preserves_query_byte
= (ecx & 0xff) == (ccd->qr[ccd->used].r.ecx & 0xff);
++ccd->used;
return true;
}
/* Collected CPUID data into *CCD. If LIMIT, apply per-leaf limits to
avoid exceeding the pre-allocated space. Return true if all data
could be stored, false if the retrying without a limit is
requested. */
static bool
_dl_diagnostics_cpuid_collect_1 (struct cpuid_collected_data *ccd, bool limit)
{
ccd->used = 0;
ccd->ecx_limit
= (limit ? cpuid_subleaf_limit : cpuid_initial_subleaf_limit) - 1;
_dl_diagnostics_cpuid_store (ccd, 0x00, 0x00);
if (ccd->used == 0)
/* CPUID reported all 0. Should not happen. */
return true;
unsigned int maximum_leaf = ccd->qr[0x00].r.eax;
if (limit && maximum_leaf >= cpuid_main_leaf_limit)
maximum_leaf = cpuid_main_leaf_limit - 1;
for (unsigned int eax = 1; eax <= maximum_leaf; ++eax)
{
for (unsigned int ecx = 0; ecx <= ccd->ecx_limit; ++ecx)
if (!_dl_diagnostics_cpuid_store (ccd, eax, ecx))
return false;
}
if (!_dl_diagnostics_cpuid_store (ccd, cpuid_extended_leaf_offset, 0x00))
return false;
maximum_leaf = ccd->qr[ccd->used - 1].r.eax;
if (maximum_leaf < cpuid_extended_leaf_offset)
/* No extended CPUID information. */
return true;
if (limit
&& maximum_leaf - cpuid_extended_leaf_offset >= cpuid_main_leaf_limit)
maximum_leaf = cpuid_extended_leaf_offset + cpuid_main_leaf_limit - 1;
for (unsigned int eax = cpuid_extended_leaf_offset + 1;
eax <= maximum_leaf; ++eax)
{
for (unsigned int ecx = 0; ecx <= ccd->ecx_limit; ++ecx)
if (!_dl_diagnostics_cpuid_store (ccd, eax, ecx))
return false;
}
return true;
}
/* Call _dl_diagnostics_cpuid_collect_1 twice if necessary, the
second time with the limit applied. */
static void
_dl_diagnostics_cpuid_collect (struct cpuid_collected_data *ccd)
{
if (!_dl_diagnostics_cpuid_collect_1 (ccd, false))
_dl_diagnostics_cpuid_collect_1 (ccd, true);
/* Re-use the result of the official feature probing here. */
const struct cpu_features *cpu_features = __get_cpu_features ();
if (CPU_FEATURES_CPU_P (cpu_features, OSXSAVE))
{
unsigned int xcrlow;
unsigned int xcrhigh;
asm ("xgetbv" : "=a" (xcrlow), "=d" (xcrhigh) : "c" (0));
ccd->xgetbv_ecx_0 = ((uint64_t) xcrhigh << 32) + xcrlow;
}
else
ccd->xgetbv_ecx_0 = 0;
}
/* Print a CPUID register value (passed as REG_VALUE) if it differs
from the expected REG_REFERENCE value. PROCESSOR_INDEX is the
process sequence number (always starting at zero; not a kernel ID). */
static void
_dl_diagnostics_cpuid_print_reg (unsigned int processor_index,
const struct cpuid_query *q,
const char *reg_label, unsigned int reg_value,
bool subleaf)
{
if (subleaf)
_dl_printf ("x86.processor[0x%x].cpuid.subleaf_eax[0x%x]"
".ecx[0x%x].%s=0x%x\n",
processor_index, q->eax, q->ecx_first, reg_label, reg_value);
else
_dl_printf ("x86.processor[0x%x].cpuid.eax[0x%x].%s=0x%x\n",
processor_index, q->eax, reg_label, reg_value);
}
/* Print CPUID result values in *RESULT for the query in
CCD->qr[CCD_IDX]. PROCESSOR_INDEX is the process sequence number
(always starting at zero; not a kernel ID). */
static void
_dl_diagnostics_cpuid_print_query (unsigned int processor_index,
struct cpuid_collected_data *ccd,
unsigned int ccd_idx,
const struct cpuid_registers *result)
{
/* Treat this as a value if subleaves if ecx isn't zero (maybe
within the [ecx_fist, ecx_last] range), or if eax matches its
neighbors. If the range is [0, ecx_limit], then the subleaves
are not distinct (independently of ecx_preserves_query_byte),
so do not report them separately. */
struct cpuid_query *q = &ccd->qr[ccd_idx].q;
bool subleaf = (q->ecx_first > 0
|| (q->ecx_first != q->ecx_last
&& !(q->ecx_first == 0 && q->ecx_last == ccd->ecx_limit))
|| (ccd_idx > 0 && q->eax == ccd->qr[ccd_idx - 1].q.eax)
|| (ccd_idx + 1 < ccd->used
&& q->eax == ccd->qr[ccd_idx + 1].q.eax));
_dl_diagnostics_cpuid_print_reg (processor_index, q, "eax", result->eax,
subleaf);
_dl_diagnostics_cpuid_print_reg (processor_index, q, "ebx", result->ebx,
subleaf);
_dl_diagnostics_cpuid_print_reg (processor_index, q, "ecx", result->ecx,
subleaf);
_dl_diagnostics_cpuid_print_reg (processor_index, q, "edx", result->edx,
subleaf);
if (subleaf && q->ecx_first != q->ecx_last)
{
_dl_printf ("x86.processor[0x%x].cpuid.subleaf_eax[0x%x]"
".ecx[0x%x].until_ecx=0x%x\n",
processor_index, q->eax, q->ecx_first, q->ecx_last);
if (q->ecx_preserves_query_byte)
_dl_printf ("x86.processor[0x%x].cpuid.subleaf_eax[0x%x]"
".ecx[0x%x].ecx_query_mask=0xff\n",
processor_index, q->eax, q->ecx_first);
}
}
/* Perform differential reporting of the data in *CURRENT against
*BASE. REQUESTED_CPU is the kernel CPU ID the thread was
configured to run on, or -1 if no configuration was possible.
PROCESSOR_INDEX is the process sequence number (always starting at
zero; not a kernel ID). */
static void
_dl_diagnostics_cpuid_report (struct dl_iterate_cpu *dci,
struct cpuid_collected_data *current,
struct cpuid_collected_data *base)
{
if (dci->requested_cpu >= 0)
_dl_printf ("x86.processor[0x%x].requested=0x%x\n",
dci->processor_index, dci->requested_cpu);
if (dci->actual_cpu >= 0)
_dl_printf ("x86.processor[0x%x].observed=0x%x\n",
dci->processor_index, dci->actual_cpu);
if (dci->actual_node >= 0)
_dl_printf ("x86.processor[0x%x].observed_node=0x%x\n",
dci->processor_index, dci->actual_node);
_dl_printf ("x86.processor[0x%x].cpuid_leaves=0x%x\n",
dci->processor_index, current->used);
_dl_printf ("x86.processor[0x%x].ecx_limit=0x%x\n",
dci->processor_index, current->ecx_limit);
unsigned int base_idx = 0;
for (unsigned int current_idx = 0; current_idx < current->used;
++current_idx)
{
/* Report missing data on the current CPU as 0. */
unsigned long long int current_query
= cpuid_query_combined (&current->qr[current_idx].q);
while (base_idx < base->used
&& cpuid_query_combined (&base->qr[base_idx].q) < current_query)
{
_dl_diagnostics_cpuid_print_query (dci->processor_index,
base, base_idx,
&cpuid_registers_zero);
++base_idx;
}
if (base_idx < base->used
&& cpuid_query_combined (&base->qr[base_idx].q) == current_query)
{
_Static_assert (sizeof (struct cpuid_registers) == 4 * 4,
"no padding in struct cpuid_registers");
if (current->qr[current_idx].q.ecx_last
!= base->qr[base_idx].q.ecx_last
|| memcmp (&current->qr[current_idx].r,
&base->qr[base_idx].r,
sizeof (struct cpuid_registers)) != 0)
/* The ECX range or the values have changed. Show the
new values. */
_dl_diagnostics_cpuid_print_query (dci->processor_index,
current, current_idx,
&current->qr[current_idx].r);
++base_idx;
}
else
/* Data is absent in the base reference. Report the new data. */
_dl_diagnostics_cpuid_print_query (dci->processor_index,
current, current_idx,
&current->qr[current_idx].r);
}
if (current->xgetbv_ecx_0 != base->xgetbv_ecx_0)
{
/* Re-use the 64-bit printing routine. */
_dl_printf ("x86.processor[0x%x].", dci->processor_index);
_dl_diagnostics_print_labeled_value ("xgetbv.ecx[0x0]",
current->xgetbv_ecx_0);
}
}
static void
_dl_diagnostics_cpuid (void)
{
#if !HAS_CPUID
/* CPUID is not supported, so there is nothing to dump. */
if (__get_cpuid_max (0, 0) == 0)
return;
#endif
struct dl_iterate_cpu dic;
_dl_iterate_cpu_init (&dic);
/* Two copies of the data are used. Data is written to the index
(dic.processor_index & 1). The previous version against which the
data dump is reported is at index !(processor_index & 1). */
struct cpuid_collected_data ccd[2];
/* The initial data is presumed to be all zero. Zero results are
not recorded. */
ccd[1].used = 0;
ccd[1].xgetbv_ecx_0 = 0;
/* Run the CPUID probing on a specific CPU. There are expected
differences for encoding core IDs and topology information in
CPUID output, but some firmware/kernel bugs also may result in
asymmetric data across CPUs in some cases. */
while (_dl_iterate_cpu_next (&dic))
{
_dl_diagnostics_cpuid_collect (&ccd[dic.processor_index & 1]);
_dl_diagnostics_cpuid_report
(&dic, &ccd[dic.processor_index & 1],
&ccd[!(dic.processor_index & 1)]);
}
}