[PATCH 2/3] gdb: Add soname to build-id mapping for corefiles
Aaron Merey
amerey@redhat.com
Wed Nov 17 03:24:41 GMT 2021
Hi Simon,
On Sat, Nov 13, 2021 at 9:37 PM Simon Marchi <simon.marchi@polymtl.ca> wrote:
> > + filename_map[filename] = build_id = vma_map_it->second;
>
> Please avoid doing two assignments in one statement.
Fixed.
> > +gdb::optional<std::string>
> > +gdb_bfd_read_elf_soname (struct bfd *bfd)
> > +{
> > + gdb_assert (bfd != nullptr);
> > +
> > + gdb_bfd_ref_ptr abfd = gdb_bfd_open (bfd->filename, gnutarget);
>
> Can you explain why we are opening bfd->filename? Doesn't "abfd"
> represent the exact same thing than "bfd"? So why can't we use "bfd"
> directly to look up the soname?
bfd->flags does not contain the correct value. This causes the check
for ET_DYN to fail even for shared libraries. Also bfd->build_id always
seems to be NULL. Opening "abfd" with gdb_bfd_open and passing it to
bfd_check_format populates flags and build_id with the correct values.
Passing "bfd" to bfd_check_format still does not populate these fields
with the correct values.
It looks like this happens because the format of "abfd" is initially
set to bfd_unknown. In this case bfd_check_format rereads the file and
updates some fields with the correct values, including flags and build_id.
Since format of "bfd" is instead bfd_object, bfd_check_format returns
early and skips updating any fields.
Thanks,
Aaron
>From 275e69ce65aa3d5ee3b017175c73f8536a1fb559 Mon Sep 17 00:00:00 2001
From: Aaron Merey <amerey@redhat.com>
Date: Tue, 16 Nov 2021 17:33:52 -0500
Subject: [PATCH 2/3] gdb: Add soname to build-id mapping for core files
Since commit aa2d5a422 gdb has been able to read executable and shared
library build-ids within core files.
Expand this functionality so that each program_space maintains a map of
soname to build-id for each shared library referenced in the program_space's
core file.
This feature may be used to verify that gdb has found the correct shared
libraries for core files and to facilitate downloading shared libaries via
debuginfod.
---
gdb/corelow.c | 11 +++++++++++
gdb/linux-tdep.c | 38 +++++++++++++++++++++++++++++++++++++-
gdb/progspace.c | 32 ++++++++++++++++++++++++++++++++
gdb/progspace.h | 18 ++++++++++++++++++
gdb/solib.c | 35 +++++++++++++++++++++++++++++++++++
gdb/solib.h | 5 +++++
6 files changed, 138 insertions(+), 1 deletion(-)
diff --git a/gdb/corelow.c b/gdb/corelow.c
index 10942e6af01..d1256a9e99b 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -282,6 +282,16 @@ core_target::build_file_mappings ()
/* Set target_section fields. */
m_core_file_mappings.emplace_back (start, end, sec);
+
+ /* If this is a bfd of a shared library, record its soname
+ and build id. */
+ if (build_id != nullptr)
+ {
+ gdb::optional<std::string> soname = gdb_bfd_read_elf_soname (bfd);
+ if (soname)
+ current_program_space->set_cbfd_soname_build_id
+ (std::move (*soname), build_id);
+ }
});
normalize_mem_ranges (&m_core_unavailable_mappings);
@@ -305,6 +315,7 @@ core_target::close ()
comments in clear_solib in solib.c. */
clear_solib ();
+ current_program_space->clear_cbfd_soname_build_ids ();
current_program_space->cbfd.reset (nullptr);
}
diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index e2cff83086a..7325ba67208 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -44,6 +44,7 @@
#include "solib-svr4.h"
#include <ctype.h>
+#include <unordered_map>
/* This enum represents the values that the user can choose when
informing the Linux kernel about which memory mappings will be
@@ -1170,6 +1171,23 @@ linux_read_core_file_mappings
if (f != descend)
warning (_("malformed note - filename area is too big"));
+ const bfd_build_id *orig_build_id = cbfd->build_id;
+ std::unordered_map<ULONGEST, const bfd_build_id *> vma_map;
+ std::unordered_map<char *, const bfd_build_id *> filename_map;
+
+ /* Search for solib build-ids in the core file. Each time one is found,
+ map the start vma of the corresponding elf header to the build-id. */
+ for (bfd_section *sec = cbfd->sections; sec != nullptr; sec = sec->next)
+ {
+ cbfd->build_id = nullptr;
+
+ if (sec->flags & SEC_LOAD
+ && get_elf_backend_data (cbfd)->elf_backend_core_find_build_id
+ (cbfd, (bfd_vma) sec->filepos))
+ vma_map[sec->vma] = cbfd->build_id;
+ }
+
+ cbfd->build_id = orig_build_id;
pre_loop_cb (count);
for (int i = 0; i < count; i++)
@@ -1183,8 +1201,26 @@ linux_read_core_file_mappings
descdata += addr_size;
char * filename = filenames;
filenames += strlen ((char *) filenames) + 1;
+ const bfd_build_id *build_id = nullptr;
+ auto vma_map_it = vma_map.find (start);
+
+ /* Map filename to the build-id associated with this start vma,
+ if such a build-id was found. Otherwise use the build-id
+ already associated with this filename if it exists. */
+ if (vma_map_it != vma_map.end ())
+ {
+ build_id = vma_map_it->second;
+ filename_map[filename] = build_id;
+ }
+ else
+ {
+ auto filename_map_it = filename_map.find (filename);
+
+ if (filename_map_it != filename_map.end ())
+ build_id = filename_map_it->second;
+ }
- loop_cb (i, start, end, file_ofs, filename, nullptr);
+ loop_cb (i, start, end, file_ofs, filename, build_id);
}
}
diff --git a/gdb/progspace.c b/gdb/progspace.c
index 7080bf8ee27..680c5ba8f0a 100644
--- a/gdb/progspace.c
+++ b/gdb/progspace.c
@@ -18,6 +18,7 @@
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "defs.h"
+#include "build-id.h"
#include "gdbcmd.h"
#include "objfiles.h"
#include "arch-utils.h"
@@ -358,6 +359,37 @@ print_program_space (struct ui_out *uiout, int requested)
}
}
+/* See progspace.h. */
+
+void
+program_space::set_cbfd_soname_build_id (std::string soname,
+ const bfd_build_id *build_id)
+{
+ m_cbfd_soname_to_build_id[std::move (soname)] = build_id_to_string (build_id);
+}
+
+/* See progspace.h. */
+
+const char *
+program_space::get_cbfd_soname_build_id (const char *soname)
+{
+ gdb_assert (soname);
+
+ auto it = m_cbfd_soname_to_build_id.find (basename (soname));
+ if (it == m_cbfd_soname_to_build_id.end ())
+ return nullptr;
+
+ return it->second.c_str ();
+}
+
+/* See progspace.h. */
+
+void
+program_space::clear_cbfd_soname_build_ids ()
+{
+ m_cbfd_soname_to_build_id.clear ();
+}
+
/* Boolean test for an already-known program space id. */
static int
diff --git a/gdb/progspace.h b/gdb/progspace.h
index fb348ca7539..01af5a387e3 100644
--- a/gdb/progspace.h
+++ b/gdb/progspace.h
@@ -30,6 +30,7 @@
#include "gdbsupport/safe-iterator.h"
#include <list>
#include <vector>
+#include <unordered_map>
struct target_ops;
struct bfd;
@@ -324,6 +325,19 @@ struct program_space
/* Binary file diddling handle for the core file. */
gdb_bfd_ref_ptr cbfd;
+ /* Associate a core file SONAME with BUILD_ID so that it can be retrieved
+ with get_cbfd_soname_build_id. */
+ void set_cbfd_soname_build_id (std::string soname,
+ const bfd_build_id *build_id);
+
+ /* If a core file SONAME had a build-id associated with it by a previous
+ call to set_cbfd_soname_build_id then return the build-id as a
+ NULL-terminated hex string. */
+ const char *get_cbfd_soname_build_id (const char *soname);
+
+ /* Clear all core file soname to build-id mappings. */
+ void clear_cbfd_soname_build_ids ();
+
/* The address space attached to this program space. More than one
program space may be bound to the same address space. In the
traditional unix-like debugging scenario, this will usually
@@ -378,6 +392,10 @@ struct program_space
/* The set of target sections matching the sections mapped into
this program space. Managed by both exec_ops and solib.c. */
target_section_table m_target_sections;
+
+ /* Mapping of a core file's shared library sonames to their
+ respective build-ids. */
+ std::unordered_map<std::string, std::string> m_cbfd_soname_to_build_id;
};
/* An address space. It is used for comparing if
diff --git a/gdb/solib.c b/gdb/solib.c
index 3947c2d1d2e..c0beea19d7b 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -23,6 +23,7 @@
#include <fcntl.h>
#include "symtab.h"
#include "bfd.h"
+#include "build-id.h"
#include "symfile.h"
#include "objfiles.h"
#include "gdbcore.h"
@@ -1586,6 +1587,40 @@ gdb_bfd_scan_elf_dyntag (const int desired_dyntag, bfd *abfd, CORE_ADDR *ptr,
return 0;
}
+/* See solib.h. */
+
+gdb::optional<std::string>
+gdb_bfd_read_elf_soname (struct bfd *bfd)
+{
+ gdb_assert (bfd != nullptr);
+
+ gdb_bfd_ref_ptr abfd = gdb_bfd_open (bfd->filename, gnutarget);
+
+ if (abfd == nullptr)
+ return {};
+
+ /* Check that bfd is an ET_DYN ELF file. */
+ bfd_check_format (abfd.get (), bfd_object);
+ if (!(bfd_get_file_flags (abfd.get ()) & DYNAMIC))
+ return {};
+
+ /* Determine soname of shared library. If found map soname to build-id. */
+ CORE_ADDR idx;
+ if (!gdb_bfd_scan_elf_dyntag (DT_SONAME, abfd.get (), &idx, nullptr))
+ return {};
+
+ struct bfd_section *dynstr = bfd_get_section_by_name (abfd.get (), ".dynstr");
+ if (dynstr == nullptr || bfd_section_size (dynstr) <= idx)
+ return {};
+
+ /* Read the soname from the string table. */
+ gdb::byte_vector dynstr_buf;
+ if (!gdb_bfd_get_full_section_contents (abfd.get (), dynstr, &dynstr_buf))
+ return {};
+
+ return std::string ((const char *)dynstr_buf.data () + idx);
+}
+
/* Lookup the value for a specific symbol from symbol table. Look up symbol
from ABFD. MATCH_SYM is a callback function to determine whether to pick
up a symbol. DATA is the input of this callback function. Return NULL
diff --git a/gdb/solib.h b/gdb/solib.h
index c50f74e06bf..51cc047463f 100644
--- a/gdb/solib.h
+++ b/gdb/solib.h
@@ -118,6 +118,11 @@ extern CORE_ADDR gdb_bfd_lookup_symbol_from_symtab (bfd *abfd,
extern int gdb_bfd_scan_elf_dyntag (const int desired_dyntag, bfd *abfd,
CORE_ADDR *ptr, CORE_ADDR *ptr_addr);
+/* If BFD is an ELF shared object then attempt to return the string
+ referred to by its DT_SONAME tag. */
+
+extern gdb::optional<std::string> gdb_bfd_read_elf_soname (struct bfd *bfd);
+
/* Enable or disable optional solib event breakpoints as appropriate. */
extern void update_solib_breakpoints (void);
--
2.31.1
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