[PATCH v3 1/2] perf env: Add perf_env__e_machine helper and use in perf_env__arch

Ian Rogers
2026-03-26T17:45:28Z

Add a helper that lazily computes the e_machine and falls back of
EM_HOST. Use the perf_env's arch to compute the e_machine if
available. Use a binary search for some efficiency in this, but handle
somewhat complex duplicate rules. Switch perf_env__arch to be derived
the e_machine for consistency. This switches arch from being uname
derived to matching that of the perf binary (via EM_HOST). Update
session to use the helper, which may mean using EM_HOST when no
threads are available. This also updates the perf data file header
that gets the e_machine/e_flags from the session.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/env.c | 179 ++++++++++++++++++++++++++++++--------
tools/perf/util/env.h | 1 +
tools/perf/util/session.c | 14 +--
3 files changed, 151 insertions(+), 43 deletions(-)

diff --git a/tools/perf/util/env.c b/tools/perf/util/env.c
index 93d475a80f14..304bd8245485 100644
--- a/tools/perf/util/env.c
+++ b/tools/perf/util/env.c
@@ -1,10 +1,12 @@
// SPDX-License-Identifier: GPL-2.0
#include "cpumap.h"
+#include "dwarf-regs.h"
#include "debug.h"
#include "env.h"
#include "util/header.h"
#include "util/rwsem.h"
#include <linux/compiler.h>
+#include <linux/kernel.h>
#include <linux/ctype.h>
#include <linux/rbtree.h>
#include <linux/string.h>
@@ -588,51 +590,154 @@ void cpu_cache_level__free(struct cpu_cache_level *cache)
zfree(&cache->size);
}

+struct arch_to_e_machine {
+ const char *prefix;
+ uint16_t e_machine;
+};
+
/*
- * Return architecture name in a normalized form.
- * The conversion logic comes from the Makefile.
+ * A mapping from an arch prefix string to an ELF machine that can be used in a
+ * bsearch. Some arch prefixes are shared an need additional processing as
+ * marked next to the architecture. The prefixes handle both perf's architecture
+ * naming and those from uname.
*/
-static const char *normalize_arch(char *arch)
-{
- if (!strcmp(arch, "x86_64"))
- return "x86";
- if (arch[0] == 'i' && arch[2] == '8' && arch[3] == '6')
- return "x86";
- if (!strcmp(arch, "sun4u") || !strncmp(arch, "sparc", 5))
- return "sparc";
- if (!strncmp(arch, "aarch64", 7) || !strncmp(arch, "arm64", 5))
- return "arm64";
- if (!strncmp(arch, "arm", 3) || !strcmp(arch, "sa110"))
- return "arm";
- if (!strncmp(arch, "s390", 4))
- return "s390";
- if (!strncmp(arch, "parisc", 6))
- return "parisc";
- if (!strncmp(arch, "powerpc", 7) || !strncmp(arch, "ppc", 3))
- return "powerpc";
- if (!strncmp(arch, "mips", 4))
- return "mips";
- if (!strncmp(arch, "sh", 2) && isdigit(arch[2]))
- return "sh";
- if (!strncmp(arch, "loongarch", 9))
- return "loongarch";
-
- return arch;
+static const struct arch_to_e_machine prefix_to_e_machine[] = {
+ {"aarch64", EM_AARCH64},
+ {"alpha", EM_ALPHA},
+ {"arc", EM_ARC},
+ {"arm", EM_ARM}, /* Check also for EM_AARCH64. */
+ {"avr", EM_AVR}, /* Check also for EM_AVR32. */
+ {"bfin", EM_BLACKFIN},
+ {"blackfin", EM_BLACKFIN},
+ {"cris", EM_CRIS},
+ {"csky", EM_CSKY},
+ {"hppa", EM_PARISC},
+ {"i386", EM_386},
+ {"i486", EM_386},
+ {"i586", EM_386},
+ {"i686", EM_386},
+ {"loongarch", EM_LOONGARCH},
+ {"m32r", EM_M32R},
+ {"m68k", EM_68K},
+ {"microblaze", EM_MICROBLAZE},
+ {"mips", EM_MIPS},
+ {"msp430", EM_MSP430},
+ {"parisc", EM_PARISC},
+ {"powerpc", EM_PPC}, /* Check also for EM_PPC64. */
+ {"ppc", EM_PPC}, /* Check also for EM_PPC64. */
+ {"riscv", EM_RISCV},
+ {"sa110", EM_ARM},
+ {"s390", EM_S390},
+ {"sh", EM_SH},
+ {"sparc", EM_SPARC}, /* Check also for EM_SPARCV9. */
+ {"sun4u", EM_SPARC},
+ {"x86", EM_X86_64}, /* Check also for EM_386. */
+ {"xtensa", EM_XTENSA},
+};
+
+static int compare_prefix(const void *key, const void *element)
+{
+ const char *search_key = key;
+ const struct arch_to_e_machine *map_element = element;
+ size_t prefix_len = strlen(map_element->prefix);
+
+ return strncmp(search_key, map_element->prefix, prefix_len);
+}
+
+static uint16_t perf_arch_to_e_machine(const char *perf_arch, bool is_64_bit)
+{
+ /* Binary search for a matching prefix. */
+ const struct arch_to_e_machine *result;
+
+ if (!perf_arch)
+ return EM_HOST;
+
+ result = bsearch(perf_arch,
+ prefix_to_e_machine, ARRAY_SIZE(prefix_to_e_machine),
+ sizeof(prefix_to_e_machine[0]),
+ compare_prefix);
+
+ if (!result) {
+ pr_debug("Unknown perf arch for ELF machine mapping: %s\n", perf_arch);
+ return EM_NONE;
+ }
+
+ /* Handle conflicting prefixes. */
+ switch (result->e_machine) {
+ case EM_ARM:
+ return !strcmp(perf_arch, "arm64") ? EM_AARCH64 : EM_ARM;
+ case EM_AVR:
+ return !strcmp(perf_arch, "avr32") ? EM_AVR32 : EM_AVR;
+ case EM_PPC:
+ return is_64_bit || strstarts(perf_arch, "ppc64") ? EM_PPC64 : EM_PPC;
+ case EM_SPARC:
+ return is_64_bit || !strcmp(perf_arch, "sparc64") ? EM_SPARCV9 : EM_SPARC;
+ case EM_X86_64:
+ return is_64_bit || !strcmp(perf_arch, "x86_64") ? EM_X86_64 : EM_386;
+ default:
+ return result->e_machine;
+ }
+}
+
+static const char *e_machine_to_perf_arch(uint16_t e_machine)
+{
+ /*
+ * Table for if either the perf arch string differs from uname or there
+ * are >1 ELF machine with the prefix.
+ */
+ static const struct arch_to_e_machine extras[] = {
+ {"arm64", EM_AARCH64},
+ {"avr32", EM_AVR32},
+ {"powerpc", EM_PPC},
+ {"powerpc", EM_PPC64},
+ {"sparc", EM_SPARCV9},
+ {"x86", EM_386},
+ {"x86", EM_X86_64},
+ {"none", EM_NONE},
+ };
+
+ for (size_t i = 0; i < ARRAY_SIZE(extras); i++) {
+ if (extras[i].e_machine == e_machine)
+ return extras[i].prefix;
+ }
+
+ for (size_t i = 0; i < ARRAY_SIZE(prefix_to_e_machine); i++) {
+ if (prefix_to_e_machine[i].e_machine == e_machine)
+ return prefix_to_e_machine[i].prefix;
+
+ }
+ return "unknown";
+}
+
+uint16_t perf_env__e_machine(struct perf_env *env, uint32_t *e_flags)
+{
+ if (!env) {
+ if (e_flags)
+ *e_flags = EF_HOST;
+
+ return EM_HOST;
+ }
+ if (env->e_machine == EM_NONE) {
+ env->e_machine = perf_arch_to_e_machine(env->arch, env->kernel_is_64_bit);
+
+ if (env->e_machine == EM_HOST)
+ env->e_flags = EF_HOST;
+ }
+ if (e_flags)
+ *e_flags = EF_HOST;
+
+ return env->e_machine;
}

const char *perf_env__arch(struct perf_env *env)
{
- char *arch_name;
+ if (!env)
+ return e_machine_to_perf_arch(EM_HOST);

- if (!env || !env->arch) { /* Assume local operation */
- static struct utsname uts = { .machine[0] = '\0', };
- if (uts.machine[0] == '\0' && uname(&uts) < 0)
- return NULL;
- arch_name = uts.machine;
- } else
- arch_name = env->arch;
+ if (!env->arch)
+ env->arch = strdup(e_machine_to_perf_arch(perf_env__e_machine(env, /*e_flags=*/NULL)));

- return normalize_arch(arch_name);
+ return env->arch;
}

#if defined(HAVE_LIBTRACEEVENT)
diff --git a/tools/perf/util/env.h b/tools/perf/util/env.h
index a4501cbca375..91ff252712f4 100644
--- a/tools/perf/util/env.h
+++ b/tools/perf/util/env.h
@@ -186,6 +186,7 @@ int perf_env__read_cpu_topology_map(struct perf_env *env);

void cpu_cache_level__free(struct cpu_cache_level *cache);

+uint16_t perf_env__e_machine(struct perf_env *env, uint32_t *e_flags);
const char *perf_env__arch(struct perf_env *env);
const char *perf_env__arch_strerrno(struct perf_env *env, int err);
const char *perf_env__cpuid(struct perf_env *env);
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 4b465abfa36c..dcc9bef303aa 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -2996,14 +2996,16 @@ uint16_t perf_session__e_machine(struct perf_session *session, uint32_t *e_flags
return EM_HOST;
}

+ /* Is the env caching an e_machine? */
env = perf_session__env(session);
- if (env && env->e_machine != EM_NONE) {
- if (e_flags)
- *e_flags = env->e_flags;
-
- return env->e_machine;
- }
+ if (env && env->e_machine != EM_NONE)
+ return perf_env__e_machine(env, e_flags);

+ /*
+ * Compute from threads, note this is more accurate than
+ * perf_env__e_machine that falls back on EM_HOST and doesn't consider
+ * mixed 32-bit and 64-bit threads.
+ */
machines__for_each_thread(&session->machines,
perf_session__e_machine_cb,
&args);
--
2.53.0.1018.g2bb0e51243-goog