Re: [patch 6/6] gdbserver build-id attribute generator

Aleksandar Ristovski
2013-03-22T13:20:44Z

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This is the final patch that does actual addition of build-id attribute
to qxfer_libraries.

* doc/gdb.texinfo (Library List Format for SVR4 Targets): Add
'build-id' in description, example, new attribute in dtd.
* linux-low.c (linux-maps.h, search.h): Include.
(struct build_id_list): New structure.
(build_id_list_s): New typedef, new vector type def.
(free_build_id_list, compare_build_id_list,
compare_build_id_list_range, compare_build_id_list_inode): New.
(struct find_memory_region_callback_data): New.
(find_memory_region_callback): New fwd. declaration.
(read_build_id, find_memory_region_callback, get_hex_build_id): New.
(linux_qxfer_libraries_svr4): Add optional build-id attribute
to reply XML document.

Thanks,

Aleksandar

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diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4ac28bb..5ff9e95 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -40404,6 +40404,9 @@ memory address. It is a displacement of absolute memory address against
address the file was prelinked to during the library load.
@item
@code{l_ld}, which is memory address of the @code{PT_DYNAMIC} segment
+@item
+@code{build-id}, hex encoded @code{.note.gnu.build-id} section, if such
+section exists.
@end itemize

Additionally the single @code{main-lm} attribute specifies address of
@@ -40421,7 +40424,7 @@ looks like this:
<library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000"
l_ld="0xe4eefc"/>
<library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000"
- l_ld="0x152350"/>
+ l_ld="0x152350" build-id="9afccf7cc41e6293476223fe72480854"/>
</library-list-svr>
@end smallexample

@@ -40437,6 +40440,7 @@ The format of an SVR4 library list is described by this DTD:
<!ATTLIST library lm CDATA #REQUIRED>
<!ATTLIST library l_addr CDATA #REQUIRED>
<!ATTLIST library l_ld CDATA #REQUIRED>
+<!ATTLIST library build-id CDATA #IMPLIED>
@end smallexample

@node Memory Map Format
diff --git a/gdb/features/library-list-svr4.dtd b/gdb/features/library-list-svr4.dtd
index cae7fd8..e4409ba 100644
--- a/gdb/features/library-list-svr4.dtd
+++ b/gdb/features/library-list-svr4.dtd
@@ -14,3 +14,4 @@
<!ATTLIST library lm CDATA #REQUIRED>
<!ATTLIST library l_addr CDATA #REQUIRED>
<!ATTLIST library l_ld CDATA #REQUIRED>
+<!ATTLIST library build-id CDATA #IMPLIED>
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 523926d..8bbb5ba 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -20,6 +20,7 @@
#include "linux-low.h"
#include "linux-osdata.h"
#include "agent.h"
+#include "linux-maps.h"

#include "gdb_wait.h"
#include <stdio.h>
@@ -43,6 +44,7 @@
#include "gdb_stat.h"
#include <sys/vfs.h>
#include <sys/uio.h>
+#include <search.h>
#ifndef ELFMAG0
/* Don't include <linux/elf.h> here. If it got included by gdb_proc_service.h
then ELFMAG0 will have been defined. If it didn't get included by
@@ -5643,6 +5645,265 @@ struct link_map_offsets
int l_prev_offset;
};

+
+/* Structure for holding all mappings. Only mapping
+ containing l_ld can have hex_build_id set. */
+
+struct build_id_list
+{
+ ULONGEST vaddr;
+
+ ULONGEST size;
+
+ ULONGEST offset;
+
+ ULONGEST inode;
+
+ const char *filename;
+ int read:1;
+ int write:1;
+ int exec:1;
+ int modified:1;
+
+ /* build_id is hex encoded string allocated using malloc, and
+ needs to be freed. */
+
+ char *hex_build_id;
+};
+
+typedef struct build_id_list build_id_list_s;
+
+DEF_VEC_O(build_id_list_s);
+
+static void
+free_build_id_list (VEC (build_id_list_s) *lst)
+{
+ if (VEC_length (build_id_list_s, lst))
+ {
+ int ix;
+ build_id_list_s *p;
+
+ for (ix = 0; VEC_iterate (build_id_list_s, lst, ix, p); ++ix)
+ xfree (p->hex_build_id);
+ }
+
+ VEC_free (build_id_list_s, lst);
+}
+
+/* Used for qsort-ing list by vaddr. */
+
+static int
+compare_build_id_list (const void *const b1,
+ const void *const b2)
+{
+ const build_id_list_s *const p1 = b1;
+ const build_id_list_s *const p2 = b2;
+
+ if (p1->vaddr > p2->vaddr)
+ return 1;
+ if (p1->vaddr < p2->vaddr)
+ return -1;
+ return 0;
+}
+
+/* Used for finding a mapping containing the given
+ l_ld passed in K. */
+
+static int
+compare_build_id_list_range (const void *const k,
+ const void *const b)
+{
+ const ULONGEST key = *(CORE_ADDR*) k;
+ const build_id_list_s *const p = b;
+
+ if (key < p->vaddr)
+ return -1;
+
+ if (key < p->vaddr + p->size)
+ return 0;
+
+ return 1;
+}
+
+/* Used for linear search of the lowest vaddr for the given
+ inode. */
+
+static int
+compare_build_id_list_inode (const void *const k, const void *const b)
+{
+ const ULONGEST key = *(ULONGEST*)k;
+ const build_id_list_s *const p = b;
+
+ return !(key == p->inode);
+}
+
+struct find_memory_region_callback_data {
+ unsigned is_elf64;
+
+ /* Return. Ordered list of all object mappings sorted in
+ ascending order by VADDR. Must be freed with free_build_id_list. */
+ VEC (build_id_list_s) *list;
+};
+
+static linux_find_memory_region_ftype find_memory_region_callback;
+
+/* Read .note.gnu.build-id from PT_NOTE. */
+
+static void
+read_build_id (struct find_memory_region_callback_data *const p,
+ build_id_list_s *const bil, const CORE_ADDR load_addr,
+ const CORE_ADDR l_addr)
+{
+ union ElfXX_Ehdr
+ {
+ Elf32_Ehdr _32;
+ Elf64_Ehdr _64;
+ } ehdr;
+ union ElfXX_Phdr
+ {
+ Elf32_Phdr _32;
+ Elf64_Phdr _64;
+ } phdr;
+ union ElfXX_Nhdr
+ {
+ Elf32_Nhdr _32;
+ Elf64_Nhdr _64;
+ } *nhdr;
+#define HDR(hdr, fld) (((p)->is_elf64)? (hdr)._64.fld : (hdr)._32.fld)
+#define SIZEOFHDR(hdr) (((p)->is_elf64)?sizeof((hdr)._64):sizeof((hdr)._32))
+ if (linux_read_memory (load_addr, (unsigned char *) &ehdr, SIZEOFHDR (ehdr))
+ == 0
+ && HDR (ehdr, e_ident[EI_MAG0]) == ELFMAG0
+ && HDR (ehdr, e_ident[EI_MAG1]) == ELFMAG1
+ && HDR (ehdr, e_ident[EI_MAG2]) == ELFMAG2
+ && HDR (ehdr, e_ident[EI_MAG3]) == ELFMAG3)
+ {
+ unsigned i;
+
+ for (i = 0; i < HDR (ehdr, e_phnum); ++i)
+ {
+ if (linux_read_memory (load_addr + HDR (ehdr, e_phoff)
+ + HDR (ehdr, e_phentsize) * i,
+ (unsigned char *) &phdr,
+ HDR (ehdr, e_phentsize)) != 0)
+ {
+ warning ("Could not read program header.");
+ break;
+ }
+ if (HDR (phdr, p_type) == PT_NOTE)
+ {
+ void *const pt_note = xmalloc (HDR (phdr, p_memsz));
+ const void *const pt_end
+ = (char*)pt_note + HDR (phdr, p_memsz);
+
+ if (linux_read_memory (HDR (phdr, p_vaddr) + l_addr,
+ pt_note, HDR (phdr, p_memsz)) != 0)
+ {
+ xfree (pt_note);
+ warning ("Could not read note.");
+ break;
+ }
+
+ for (nhdr = pt_note; (void*)nhdr < pt_end;)
+ {
+ const size_t note_sz
+ = HDR (*nhdr, n_namesz) + HDR (*nhdr, n_descsz)
+ + SIZEOFHDR (*nhdr);
+
+ if ((char*)nhdr + note_sz > (char*)pt_end)
+ {
+ warning ("Malformed PT_NOTE\n");
+ break;
+ }
+ if (HDR (*nhdr, n_type) == NT_GNU_BUILD_ID)
+ {
+ /* .note.gnu.build-id. */
+ bil->hex_build_id = xmalloc (note_sz * 2 + 1);
+ bin2hex ((gdb_byte*)nhdr, bil->hex_build_id, note_sz);
+ xfree (pt_note);
+ return;
+ }
+ nhdr = (void*)((char *)nhdr + note_sz);
+ }
+ xfree (pt_note);
+ }
+ }
+ }
+ else
+ warning ("Reading build-id failed.");
+#undef HDR
+#undef SIZEOFHDR
+}
+
+
+/* Create list of build_id_list. */
+
+static int
+find_memory_region_callback (ULONGEST vaddr, ULONGEST size, ULONGEST offset,
+ ULONGEST inode, int read, int write, int exec,
+ int modified, const char *filename, void *data)
+{
+ if (inode != 0)
+ {
+ struct find_memory_region_callback_data *const p = data;
+ build_id_list_s bil;
+
+ bil.vaddr = vaddr;
+ bil.size = size;
+ bil.inode = inode;
+ bil.read = !(read == 0);
+ bil.write = !(write == 0);
+ bil.exec = !(write == 0);
+ bil.modified = !(write == 0);
+ bil.filename = filename;
+ bil.hex_build_id = NULL;
+
+ VEC_safe_push (build_id_list_s, p->list, &bil);
+ }
+
+ return 0;
+}
+
+/* Get build-id for the given L_LD. DATA must point to
+ already filled list of build_id_list elements.
+
+ Return build_id as stored in the list element corresponding
+ to L_LD.
+
+ NULL may be returned if build-id could not be fetched.
+
+ Returned string must not be freed explicitly.
+*/
+
+static const char *
+get_hex_build_id (const CORE_ADDR l_addr, const CORE_ADDR l_ld,
+ struct find_memory_region_callback_data *const data)
+{
+ build_id_list_s *const bil
+ = bsearch (&l_ld, VEC_address (build_id_list_s, data->list),
+ VEC_length (build_id_list_s, data->list),
+ sizeof (build_id_list_s), compare_build_id_list_range);
+
+ if (bil == NULL)
+ return NULL;
+
+ if (bil->hex_build_id == NULL)
+ {
+ CORE_ADDR load_addr;
+ size_t len = VEC_length (build_id_list_s, data->list);
+
+ /* Must do linear search for the first mapping of this inode. */
+ build_id_list_s *const bil_min
+ = lfind (&bil->inode, VEC_address (build_id_list_s, data->list), &len,
+ sizeof (build_id_list_s), compare_build_id_list_inode);
+ gdb_assert (bil_min != NULL && "This should never happen.");
+ load_addr = bil_min->vaddr;
+ read_build_id (data, bil, load_addr, l_addr);
+ }
+
+ return bil->hex_build_id;
+}
+
/* Construct qXfer:libraries-svr4:read reply. */

static int
@@ -5655,6 +5916,8 @@ linux_qxfer_libraries_svr4 (const char *annex, unsigned char *readbuf,
struct process_info_private *const priv = current_process ()->private;
char filename[PATH_MAX];
int pid, is_elf64;
+ struct find_memory_region_callback_data data;
+ int build_id_list_p;

static const struct link_map_offsets lmo_32bit_offsets =
{
@@ -5690,6 +5953,19 @@ linux_qxfer_libraries_svr4 (const char *annex, unsigned char *readbuf,
is_elf64 = elf_64_file_p (filename, &machine);
lmo = is_elf64 ? &lmo_64bit_offsets : &lmo_32bit_offsets;

+ data.is_elf64 = is_elf64;
+ data.list = NULL;
+ VEC_reserve (build_id_list_s, data.list, 16);
+ build_id_list_p
+ = linux_find_memory_regions_full (
+ lwpid_of (get_thread_lwp (current_inferior)),
+ find_memory_region_callback, &data, NULL) >= 0;
+
+ if (build_id_list_p)
+ qsort (VEC_address (build_id_list_s, data.list),
+ VEC_length (build_id_list_s, data.list),
+ sizeof (build_id_list_s), compare_build_id_list);
+
if (priv->r_debug == 0)
priv->r_debug = get_r_debug (pid, is_elf64);

@@ -5764,6 +6040,7 @@ linux_qxfer_libraries_svr4 (const char *annex, unsigned char *readbuf,
/* 6x the size for xml_escape_text below. */
size_t len = 6 * strlen ((char *) libname);
char *name;
+ const char *hex_enc_build_id = NULL;

if (!header_done)
{
@@ -5772,21 +6049,29 @@ linux_qxfer_libraries_svr4 (const char *annex, unsigned char *readbuf,
header_done = 1;
}

- while (allocated < p - document + len + 200)
+ name = xml_escape_text ((char *) libname);
+ if (build_id_list_p)
+ hex_enc_build_id = get_hex_build_id (l_addr, l_ld, &data);
+
+ while (allocated < (p - document + len + 200
+ + (hex_enc_build_id != NULL
+ ? strlen (hex_enc_build_id) : 0)))
{
/* Expand to guarantee sufficient storage. */
- uintptr_t document_len = p - document;
+ const ptrdiff_t document_len = p - document;

- document = xrealloc (document, 2 * allocated);
allocated *= 2;
+ document = xrealloc (document, allocated);
p = document + document_len;
}

- name = xml_escape_text ((char *) libname);
p += sprintf (p, "<library name=\"%s\" lm=\"0x%lx\" "
- "l_addr=\"0x%lx\" l_ld=\"0x%lx\"/>",
+ "l_addr=\"0x%lx\" l_ld=\"0x%lx\"",
name, (unsigned long) lm_addr,
(unsigned long) l_addr, (unsigned long) l_ld);
+ if (hex_enc_build_id != NULL)
+ p += sprintf (p, " build-id=\"%s\"", hex_enc_build_id);
+ p += sprintf(p, "/>");
free (name);
}
else if (lm_prev == 0)
@@ -5821,6 +6106,7 @@ linux_qxfer_libraries_svr4 (const char *annex, unsigned char *readbuf,

memcpy (readbuf, document + offset, len);
xfree (document);
+ free_build_id_list (data.list);

return len;
}
--
1.7.10.4