Fix: flt.lttng-utils.debug-info: build id note section non-native byte order

Issue
=====
The build id comparison code does not take into account that the target
binary file could be compiled for another architecture and thus could be
of a different byte order. This makes the build_id testcase fail on
PowerPC. The artefacts used for this testcase are compiled on x86 and
are thus in little endian as opposed to PowerPC's big endianness.

Solution
========
Parse the Elf file to extract the endianness of the binary and use that
information to change the byte order of the note section if necessary.

Drawbacks
=========
None.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: Id5d761832f9463b38ea0452da36053e885929aa9
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1246
Reviewed-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Reviewed-by: Michael Jeanson <mjeanson@efficios.com>

diff --git a/plugins/lttng-utils/debug-info/bin-info.c b/plugins/lttng-utils/debug-info/bin-info.c
index ac9bb68f8182927d17dc17ec76d4a785ea1fb8f2..5393cdbaefd54bf5fbab5cabc3bbeccb85c519e8 100644 (file)
--- a/plugins/lttng-utils/debug-info/bin-info.c
+++ b/plugins/lttng-utils/debug-info/bin-info.c
@@ -42,6 +42,8 @@
 
 #include <glib.h>
 
+#include <babeltrace/common-internal.h>
+
 #include "bin-info.h"
 #include "crc32.h"
 #include "dwarf.h"
@@ -144,6 +146,41 @@ void bin_info_destroy(struct bin_info *bin)
        g_free(bin);
 }
 
+static
+int bin_info_set_endianness(struct bin_info *bin)
+{
+       int ret, fd;
+       uint8_t e_ident[EI_NIDENT];
+
+       fd = bt_fd_cache_handle_get_fd(bin->elf_handle);
+
+       /*
+        * Read the identification fields of the elf file.
+        */
+       if (lseek(fd, 0, SEEK_SET) < 0) {
+               BT_LOGE("Error seeking the beginning of ELF file: %s",
+                       strerror(errno));
+               ret = -1;
+               goto error;
+       }
+
+       ret = bt_common_read(fd, e_ident, EI_NIDENT);
+       if (ret < EI_NIDENT) {
+               BT_LOGE_STR("Error reading the ELF identification fields");
+               ret = -1;
+               goto error;
+       }
+
+       /*
+        * Set the endianness.
+        */
+        bin->endianness = e_ident[EI_DATA];
+        ret = 0;
+
+error:
+       return ret;
+}
+
 /**
  * Initialize the ELF file for a given executable.
  *
@@ -155,6 +192,7 @@ int bin_info_set_elf_file(struct bin_info *bin)
 {
        struct bt_fd_cache_handle *elf_handle = NULL;
        Elf *elf_file = NULL;
+       int ret;
 
        if (!bin) {
                goto error;
@@ -165,21 +203,27 @@ int bin_info_set_elf_file(struct bin_info *bin)
                BT_LOGD("Failed to open %s", bin->elf_path);
                goto error;
        }
+       bin->elf_handle = elf_handle;
+
+       ret = bin_info_set_endianness(bin);
+       if (ret) {
+               goto error;
+       }
 
-       elf_file = elf_begin(bt_fd_cache_handle_get_fd(elf_handle),
+       elf_file = elf_begin(bt_fd_cache_handle_get_fd(bin->elf_handle),
                ELF_C_READ, NULL);
        if (!elf_file) {
                BT_LOGE("elf_begin failed: %s", elf_errmsg(-1));
                goto error;
        }
 
+       bin->elf_file = elf_file;
+
        if (elf_kind(elf_file) != ELF_K_ELF) {
                BT_LOGE("Error: %s is not an ELF object", bin->elf_path);
                goto error;
        }
 
-       bin->elf_handle = elf_handle;
-       bin->elf_file = elf_file;
        return 0;
 
 error:
@@ -295,7 +339,6 @@ int is_build_id_matching(struct bin_info *bin)
 {
        int ret, is_build_id, is_matching = 0;
        Elf_Scn *curr_section = NULL, *next_section = NULL;
-       Elf_Data *note_data = NULL;
        GElf_Shdr *curr_section_hdr = NULL;
 
        if (!bin->build_id) {
@@ -322,6 +365,9 @@ int is_build_id_matching(struct bin_info *bin)
        }
 
        while (next_section) {
+               Elf_Data *file_note_data = NULL;
+               Elf_Data native_note_data;
+
                curr_section = next_section;
                next_section = elf_nextscn(bin->elf_file, curr_section);
 
@@ -335,14 +381,31 @@ int is_build_id_matching(struct bin_info *bin)
                        continue;
                }
 
-               note_data = elf_getdata(curr_section, NULL);
-               if (!note_data) {
+               file_note_data = elf_getdata(curr_section, NULL);
+               if (!file_note_data) {
                        goto error;
                }
 
+               /*
+                * Prepare the destination buffer to receive the natively
+                * ordered note. The `d_buf`, `d_size`, and `d_version` fields
+                * of the destination structure must be set before invoking the
+                * `gelf_xlatetom()` function.
+                */
+               native_note_data.d_buf = g_new0(uint8_t, file_note_data->d_size);
+               BT_ASSERT(native_note_data.d_buf);
+
+               native_note_data.d_size = file_note_data->d_size;
+               native_note_data.d_version = file_note_data->d_version;
+
+               /* Translate the note data buffer to the host endianness. */
+               gelf_xlatetom(bin->elf_file, &native_note_data, file_note_data,
+                       bin->endianness);
+
                /* Check if the note is of the build-id type. */
-               is_build_id = is_build_id_note_section(note_data->d_buf);
+               is_build_id = is_build_id_note_section(native_note_data.d_buf);
                if (!is_build_id) {
+                       g_free(native_note_data.d_buf);
                        continue;
                }
 
@@ -350,8 +413,10 @@ int is_build_id_matching(struct bin_info *bin)
                 * Compare the build id of the on-disk file and
                 * the build id recorded in the trace.
                 */
-               is_matching = is_build_id_note_section_matching(note_data->d_buf,
-                               bin->build_id, bin->build_id_len);
+               is_matching = is_build_id_note_section_matching(
+                       native_note_data.d_buf, bin->build_id,
+                       bin->build_id_len);
+               g_free(native_note_data.d_buf);
                if (!is_matching) {
                        break;
                }
@@ -741,7 +806,6 @@ int bin_info_append_offset_str(const char *base_str, uint64_t low_addr,
        uint64_t offset;
        char *_result = NULL;
 
-
        if (!base_str || !result) {
                goto error;
        }

diff --git a/plugins/lttng-utils/debug-info/bin-info.h b/plugins/lttng-utils/debug-info/bin-info.h
index f6848fb3bae6c7e8ff529b39d94ce172269ab9b9..8e3a4fc685b483e33c3fbbe5b09499d2bb51c428 100644 (file)
--- a/plugins/lttng-utils/debug-info/bin-info.h
+++ b/plugins/lttng-utils/debug-info/bin-info.h
@@ -66,7 +66,12 @@ struct bin_info {
        gchar *debug_info_dir;
        /* Denotes whether the executable is position independent code. */
        bool is_pic:1;
-       /* denotes whether the build id in the trace matches to one on disk. */
+       /*
+        * Endianness of the binary file. (may differ from system endianness).
+        * Two possible values are ELFDATA2MSB and ELFDATA2LSB.
+        */
+       uint8_t endianness;
+       /* Denotes whether the build id in the trace matches to one on disk. */
        bool file_build_id_matches:1;
        /*
         * Denotes whether the executable only has ELF symbols and no