Since libebl is a private interface, subsequent patches in the series
introduce another api wrapping the libebl perf register handling. In
this patch, add an interface to access the preferred set of registers
that libdwfl would like to see to allow proper unwinding of stack
sample data.
* libdwfl/libdwfl.h (dwfl_perf_sample_preferred_regs_mask):
New function.
* libdwfl/dwfl_perf_frame.c: New file.
(dwfl_perf_sample_preferred_regs_mask): New function.
* libdw/libdw.map: Add dwfl_perf_sample_preferred_regs_mask.
* libdwfl/Makefile.am: Add dwfl_perf_frame.c.
---
libdw/libdw.map | 1 +
libdwfl/Makefile.am | 3 +-
libdwfl/dwfl_perf_frame.c | 61 +++++++++++++++++++++++++++++++++++++++
libdwfl/libdwfl.h | 10 +++++++
4 files changed, 74 insertions(+), 1 deletion(-)
create mode 100644 libdwfl/dwfl_perf_frame.c
diff --git a/libdw/libdw.map b/libdw/libdw.map
index afbc467f..3218fd9c 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -389,4 +389,5 @@ ELFUTILS_0.192 {
ELFUTILS_0.193 {
global:
dwfl_set_initial_registers_thread;
+ dwfl_perf_sample_preferred_regs_mask;
} ELFUTILS_0.192;
diff --git a/libdwfl/Makefile.am b/libdwfl/Makefile.am
index b30b86f0..37c57bee 100644
--- a/libdwfl/Makefile.am
+++ b/libdwfl/Makefile.am
@@ -2,7 +2,7 @@
##
## Process this file with automake to create Makefile.in
##
-## Copyright (C) 2005-2010, 2013 Red Hat, Inc.
+## Copyright (C) 2005-2010, 2013, 2025 Red Hat, Inc.
## This file is part of elfutils.
##
## This file is free software; you can redistribute it and/or modify
@@ -71,6 +71,7 @@ libdwfl_a_SOURCES = dwfl_begin.c dwfl_end.c dwfl_error.c
dwfl_version.c \
link_map.c core-file.c open.c image-header.c \
dwfl_frame.c frame_unwind.c dwfl_frame_pc.c \
linux-pid-attach.c linux-core-attach.c dwfl_frame_regs.c \
+ dwfl_perf_frame.c \
gzip.c debuginfod-client.c
if BZLIB
diff --git a/libdwfl/dwfl_perf_frame.c b/libdwfl/dwfl_perf_frame.c
new file mode 100644
index 00000000..87db97bc
--- /dev/null
+++ b/libdwfl/dwfl_perf_frame.c
@@ -0,0 +1,61 @@
+/* Get Dwarf Frame state for perf stack sample data.
+ Copyright (C) 2025 Red Hat, Inc.
+ This file is part of elfutils.
+
+ This file is free software; you can redistribute it and/or modify
+ it under the terms of either
+
+ * the GNU Lesser General Public License as published by the Free
+ Software Foundation; either version 3 of the License, or (at
+ your option) any later version
+
+ or
+
+ * the GNU General Public License as published by the Free
+ Software Foundation; either version 2 of the License, or (at
+ your option) any later version
+
+ or both in parallel, as here.
+
+ elfutils is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ General Public License for more details.
+
+ You should have received copies of the GNU General Public License and
+ the GNU Lesser General Public License along with this program. If
+ not, see <http://www.gnu.org/licenses/>. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <linux/perf_event.h>
+
+#include "libdwflP.h"
+
+Ebl *default_ebl = NULL;
+GElf_Half default_ebl_machine = EM_NONE;
+
+uint64_t dwfl_perf_sample_preferred_regs_mask (GElf_Half machine)
+{
+ /* XXX The most likely case is that this will only be called once,
+ for the current architecture. So we keep one Ebl* around for
+ answering this query and replace it in the unlikely case of
+ getting called with different architectures. */
+ if (default_ebl != NULL && default_ebl_machine != machine)
+ {
+ ebl_closebackend(default_ebl);
+ default_ebl = NULL;
+ }
+ if (default_ebl == NULL)
+ {
+ default_ebl = ebl_openbackend_machine(machine);
+ default_ebl_machine = machine;
+ }
+ if (default_ebl != NULL)
+ return ebl_perf_frame_regs_mask (default_ebl);
+ return 0;
+}
+
+/* XXX dwfl_perf_sample_getframes to be added in subsequent patch */
diff --git a/libdwfl/libdwfl.h b/libdwfl/libdwfl.h
index b3b32d51..29505863 100644
--- a/libdwfl/libdwfl.h
+++ b/libdwfl/libdwfl.h
@@ -825,6 +825,16 @@ int dwfl_getthread_frames (Dwfl *dwfl, pid_t tid,
void *arg)
__nonnull_attribute__ (1, 3);
+/* XXX dwfl_perf_sample_getframes to be added in subsequent patch */
+
+/* Returns the linux perf_events register mask describing a set of
+ registers sufficient for unwinding on MACHINE, or 0 if libdwfl does
+ not handle perf_events samples for MACHINE. Does not take a Dwfl*
+ or Elf* since this is meant to allow a profiling tool to configure
+ perf_events to produce meaningful data for a libdwfl session to be
+ opened later. */
+uint64_t dwfl_perf_sample_preferred_regs_mask (GElf_Half machine);
+
/* Return *PC (program counter) for thread-specific frame STATE.
Set *ISACTIVATION according to DWARF frame "activation" definition.
Typically you need to subtract 1 from *PC if *ACTIVATION is false to safely
--
2.47.0
