[binutils-gdb] gdb, gdbserver: extend RSP to support namespaces

[binutils-gdb] gdb, gdbserver: extend RSP to support namespaces

[Markus Metzger]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=2733d9d5d62c62023dc2d7a93fa5afa22f386ffd

commit 2733d9d5d62c62023dc2d7a93fa5afa22f386ffd
Author: Markus Metzger <markus.t.metzger@intel.com>
Date:   Tue Mar 15 18:08:06 2022 +0100

    gdb, gdbserver: extend RSP to support namespaces
    
    Introduce a new qXfer:libraries-svr4:read annex key/value pair
    
        lmid=<namespace identifier>
    
    to be used together with start and prev to provide the namespace of start
    and prev to gdbserver.
    
    Unknown key/value pairs are ignored by gdbserver so no new supports check
    is needed.
    
    Introduce a new library-list-svr4 library attribute
    
        lmid
    
    to provide the namespace of a library entry to GDB.
    
    This implementation uses the address of a namespace's r_debug object as
    namespace identifier.
    
    This should have incremented the minor version but since unknown XML
    attributes are ignored, anyway, and since changing the version results in
    a warning from GDB, the version is left at 1.0.

Diff:
---
 gdb/doc/gdb.texinfo                | 16 ++++++++++++++--
 gdb/features/library-list-svr4.dtd |  4 ++++
 gdb/solib-svr4.c                   | 38 +++++++++++++++++++++++++++++++++++---
 gdbserver/linux-low.cc             | 26 +++++++++++++++++---------
 4 files changed, 70 insertions(+), 14 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 3de511a4844..ea66f4ee42d 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -43706,6 +43706,12 @@ specified by the @samp{start} argument.  If unset or zero then
 the remote stub will expect that no @samp{struct link_map}
 exists prior to the starting point.
 
+@item lmid=@var{lmid}
+A hexadecimal number specifying a namespace identifier.  This is
+currently only used together with @samp{start} to provide the
+namespace identifier back to @value{GDBN} in the response.
+@value{GDBN} will only provide values that were previously reported to
+it.  If unset, the response will include @samp{lmid="0x0"}.
 @end table
 
 Arguments that are not understood by the remote stub will be silently
@@ -46244,6 +46250,11 @@ 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{lmid}, which is an identifier for a linker namespace, such as
+the memory address of the @code{r_debug} object that contains this
+namespace's load map or the namespace identifier returned by
+@code{dlinfo (3)}.
 @end itemize
 
 Additionally the single @code{main-lm} attribute specifies address of
@@ -46259,9 +46270,9 @@ looks like this:
 @smallexample
 <library-list-svr4 version="1.0" main-lm="0xe4f8f8">
   <library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000"
-           l_ld="0xe4eefc"/>
+           l_ld="0xe4eefc" lmid="0xfffe0"/>
   <library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000"
-           l_ld="0x152350"/>
+           l_ld="0x152350" lmid="0xfffe0"/>
 </library-list-svr>
 @end smallexample
 
@@ -46277,6 +46288,7 @@ 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            lmid    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 7d62354c34c..e869ff1349e 100644
--- a/gdb/features/library-list-svr4.dtd
+++ b/gdb/features/library-list-svr4.dtd
@@ -14,3 +14,7 @@
 <!ATTLIST library            lm      CDATA   #REQUIRED>
 <!ATTLIST library            l_addr  CDATA   #REQUIRED>
 <!ATTLIST library            l_ld    CDATA   #REQUIRED>
+<!-- added lmid attribute to what should have become version 1.1 but
+     since this generates a warning in GDB and since unknown attributes
+     are ignored, anyway, leaving the version at 1.0. -->
+<!ATTLIST library            lmid    CDATA   #IMPLIED>
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index a80e7e30561..295e9b8b69d 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -1067,8 +1067,37 @@ library_list_start_library (struct gdb_xml_parser *parser,
   new_elem->so_name[sizeof (new_elem->so_name) - 1] = 0;
   strcpy (new_elem->so_original_name, new_elem->so_name);
 
-  *list->tailp = new_elem;
-  list->tailp = &new_elem->next;
+  /* Older versions did not supply lmid.  Put the element into the flat
+     list of the special namespace zero in that case.  */
+  gdb_xml_value *at_lmid = xml_find_attribute (attributes, "lmid");
+  if (at_lmid == nullptr)
+    {
+      *list->tailp = new_elem;
+      list->tailp = &new_elem->next;
+    }
+  else
+    {
+      ULONGEST lmid = *(ULONGEST *) at_lmid->value.get ();
+
+      /* Ensure that the element is actually initialized.  */
+      if (list->solib_lists.find (lmid) == list->solib_lists.end ())
+	list->solib_lists[lmid] = nullptr;
+
+      so_list **psolist = &list->solib_lists[lmid];
+      so_list **pnext = psolist;
+
+      /* Walk to the end of the list if we have one.  */
+      so_list *solist = *psolist;
+      if (solist != nullptr)
+	{
+	  for (; solist->next != nullptr; solist = solist->next)
+	    /* Nothing.  */;
+
+	  pnext = &solist->next;
+	}
+
+      *pnext = new_elem;
+    }
 }
 
 /* Handle the start of a <library-list-svr4> element.  */
@@ -1108,6 +1137,7 @@ static const struct gdb_xml_attribute svr4_library_attributes[] =
   { "lm", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL },
   { "l_addr", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL },
   { "l_ld", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL },
+  { "lmid", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL },
   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 };
 
@@ -1869,7 +1899,9 @@ solist_update_incremental (svr4_info *info, CORE_ADDR debug_base,
       struct svr4_library_list library_list;
       char annex[64];
 
-      xsnprintf (annex, sizeof (annex), "start=%s;prev=%s",
+      /* Unknown key=value pairs are ignored by the gdbstub.  */
+      xsnprintf (annex, sizeof (annex), "lmid=%s;start=%s;prev=%s",
+		 phex_nz (debug_base, sizeof (debug_base)),
 		 phex_nz (lm, sizeof (lm)),
 		 phex_nz (prev_lm, sizeof (prev_lm)));
       if (!svr4_current_sos_via_xfer_libraries (&library_list, annex))
diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index e83ccceed83..4754366d443 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -6489,8 +6489,8 @@ static const link_map_offsets lmo_64bit_offsets =
 /* Get the loaded shared libraries from one namespace.  */
 
 static void
-read_link_map (std::string &document, CORE_ADDR lm_addr, CORE_ADDR lm_prev,
-	       int ptr_size, const link_map_offsets *lmo)
+read_link_map (std::string &document, CORE_ADDR lmid, CORE_ADDR lm_addr,
+	       CORE_ADDR lm_prev, int ptr_size, const link_map_offsets *lmo)
 {
   CORE_ADDR l_name, l_addr, l_ld, l_next, l_prev;
 
@@ -6525,9 +6525,9 @@ read_link_map (std::string &document, CORE_ADDR lm_addr, CORE_ADDR lm_prev,
 	  string_appendf (document, "<library name=\"");
 	  xml_escape_text_append (&document, (char *) libname);
 	  string_appendf (document, "\" lm=\"0x%s\" l_addr=\"0x%s\" "
-			  "l_ld=\"0x%s\"/>",
+			  "l_ld=\"0x%s\" lmid=\"0x%s\"/>",
 			  paddress (lm_addr), paddress (l_addr),
-			  paddress (l_ld));
+			  paddress (l_ld), paddress (lmid));
 	}
 
       lm_prev = lm_addr;
@@ -6547,7 +6547,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
   char filename[PATH_MAX];
   int pid, is_elf64;
   unsigned int machine;
-  CORE_ADDR lm_addr = 0, lm_prev = 0;
+  CORE_ADDR lmid = 0, lm_addr = 0, lm_prev = 0;
 
   if (writebuf != NULL)
     return -2;
@@ -6581,7 +6581,9 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
 	break;
 
       name_len = sep - annex;
-      if (name_len == 5 && startswith (annex, "start"))
+      if (name_len == 4 && startswith (annex, "lmid"))
+	addrp = &lmid;
+      else if (name_len == 5 && startswith (annex, "start"))
 	addrp = &lm_addr;
       else if (name_len == 4 && startswith (annex, "prev"))
 	addrp = &lm_prev;
@@ -6600,19 +6602,25 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
   std::string document = "<library-list-svr4 version=\"1.0\"";
 
   /* When the starting LM_ADDR is passed in the annex, only traverse that
-     namespace.
+     namespace, which is assumed to be identified by LMID.
 
      Otherwise, start with R_DEBUG and traverse all namespaces we find.  */
   if (lm_addr != 0)
     {
       document += ">";
-      read_link_map (document, lm_addr, lm_prev, ptr_size, lmo);
+      read_link_map (document, lmid, lm_addr, lm_prev, ptr_size, lmo);
     }
   else
     {
       if (lm_prev != 0)
 	warning ("ignoring prev=0x%s without start", paddress (lm_prev));
 
+      /* We could interpret LMID as 'provide only the libraries for this
+	 namespace' but GDB is currently only providing lmid, start, and
+	 prev, or nothing.  */
+      if (lmid != 0)
+	warning ("ignoring lmid=0x%s without start", paddress (lmid));
+
       CORE_ADDR r_debug = priv->r_debug;
       if (r_debug == 0)
 	r_debug = priv->r_debug = get_r_debug (pid, is_elf64);
@@ -6678,7 +6686,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
 		}
 	    }
 
-	  read_link_map (document, lm_addr, lm_prev, ptr_size, lmo);
+	  read_link_map (document, r_debug, lm_addr, lm_prev, ptr_size, lmo);
 
 	  if (r_version < 2)
 	    break;