accel/tcg: Add debuginfo support

Add libdw-based functions for loading and querying debuginfo. Load
debuginfo from the system and the linux-user loaders.

This is useful for the upcoming perf support, which can then put
human-readable guest symbols instead of raw guest PCs into perfmap and
jitdump files.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230112152013.125680-3-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/debuginfo.c

@@ -0,0 +1,96 @@
+/*
+ * Debug information support.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/lockable.h"
+
+#include <elfutils/libdwfl.h>
+
+#include "debuginfo.h"
+
+static QemuMutex lock;
+static Dwfl *dwfl;
+static const Dwfl_Callbacks dwfl_callbacks = {
+    .find_elf = NULL,
+    .find_debuginfo = dwfl_standard_find_debuginfo,
+    .section_address = NULL,
+    .debuginfo_path = NULL,
+};
+
+__attribute__((constructor))
+static void debuginfo_init(void)
+{
+    qemu_mutex_init(&lock);
+}
+
+void debuginfo_report_elf(const char *name, int fd, uint64_t bias)
+{
+    QEMU_LOCK_GUARD(&lock);
+
+    if (dwfl) {
+        dwfl_report_begin_add(dwfl);
+    } else {
+        dwfl = dwfl_begin(&dwfl_callbacks);
+    }
+
+    if (dwfl) {
+        dwfl_report_elf(dwfl, name, name, fd, bias, true);
+        dwfl_report_end(dwfl, NULL, NULL);
+    }
+}
+
+void debuginfo_lock(void)
+{
+    qemu_mutex_lock(&lock);
+}
+
+void debuginfo_query(struct debuginfo_query *q, size_t n)
+{
+    const char *symbol, *file;
+    Dwfl_Module *dwfl_module;
+    Dwfl_Line *dwfl_line;
+    GElf_Off dwfl_offset;
+    GElf_Sym dwfl_sym;
+    size_t i;
+    int line;
+
+    if (!dwfl) {
+        return;
+    }
+
+    for (i = 0; i < n; i++) {
+        dwfl_module = dwfl_addrmodule(dwfl, q[i].address);
+        if (!dwfl_module) {
+            continue;
+        }
+
+        if (q[i].flags & DEBUGINFO_SYMBOL) {
+            symbol = dwfl_module_addrinfo(dwfl_module, q[i].address,
+                                          &dwfl_offset, &dwfl_sym,
+                                          NULL, NULL, NULL);
+            if (symbol) {
+                q[i].symbol = symbol;
+                q[i].offset = dwfl_offset;
+            }
+        }
+
+        if (q[i].flags & DEBUGINFO_LINE) {
+            dwfl_line = dwfl_module_getsrc(dwfl_module, q[i].address);
+            if (dwfl_line) {
+                file = dwfl_lineinfo(dwfl_line, NULL, &line, 0, NULL, NULL);
+                if (file) {
+                    q[i].file = file;
+                    q[i].line = line;
+                }
+            }
+        }
+    }
+}
+
+void debuginfo_unlock(void)
+{
+    qemu_mutex_unlock(&lock);
+}