[PATCH] gdb: fix auxv caching

[Simon Marchi <simon.marchi@polymtl.ca>]

There's a flaw in the interaction of the auxv caching and the fact that
target_auxv_search allows reading auxv from an arbitrary target_ops
(passed in as a parameter).  This has consequences as explained in this
thread:

  https://inbox.sourceware.org/gdb-patches/20220719144542.1478037-1-luis.machado@arm.com/

In summary, when loading an AArch64 core file with MTE support by
passing the executable and core file names directly to GDB, we see the
MTE info:

    $ ./gdb -nx --data-directory=data-directory -q aarch64-mte-gcore aarch64-mte-gcore.core
    ...
    Program terminated with signal SIGSEGV, Segmentation fault
    Memory tag violation while accessing address 0x0000ffff8ef5e000
    Allocation tag 0x1
    Logical tag 0x0.
    #0  0x0000aaaade3d0b4c in ?? ()
    (gdb)

But if we do it as two separate commands (file and core) we don't:

    $ ./gdb -nx --data-directory=data-directory -q -ex "file aarch64-mte-gcore" -ex "core aarch64-mte-gcore.core"
    ...
    Program terminated with signal SIGSEGV, Segmentation fault.
    #0  0x0000aaaade3d0b4c in ?? ()
    (gdb)

The problem with the latter is that auxv data gets improperly cached
between the two commands.  When executing the file command, auxv gets
first queried here, when loading the executable:

    #0  target_auxv_search (ops=0x55555b842400 <exec_ops>, match=0x9, valp=0x7fffffffc5d0) at /home/simark/src/binutils-gdb/gdb/auxv.c:383
    #1  0x0000555557e576f2 in svr4_exec_displacement (displacementp=0x7fffffffc8c0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:2482
    #2  0x0000555557e594d1 in svr4_relocate_main_executable () at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:2878
    #3  0x0000555557e5989e in svr4_solib_create_inferior_hook (from_tty=1) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:2933
    #4  0x0000555557e6e49f in solib_create_inferior_hook (from_tty=1) at /home/simark/src/binutils-gdb/gdb/solib.c:1253
    #5  0x0000555557f33e29 in symbol_file_command (args=0x7fffffffe01c "aarch64-mte-gcore", from_tty=1) at /home/simark/src/binutils-gdb/gdb/symfile.c:1655
    #6  0x00005555573319c3 in file_command (arg=0x7fffffffe01c "aarch64-mte-gcore", from_tty=1) at /home/simark/src/binutils-gdb/gdb/exec.c:555
    #7  0x0000555556e47185 in do_simple_func (args=0x7fffffffe01c "aarch64-mte-gcore", from_tty=1, c=0x612000047740) at /home/simark/src/binutils-gdb/gdb/cli/cli-decode.c:95
    #8  0x0000555556e551c9 in cmd_func (cmd=0x612000047740, args=0x7fffffffe01c "aarch64-mte-gcore", from_tty=1) at /home/simark/src/binutils-gdb/gdb/cli/cli-decode.c:2543
    #9  0x00005555580e63fd in execute_command (p=0x7fffffffe02c "e", from_tty=1) at /home/simark/src/binutils-gdb/gdb/top.c:692
    #10 0x0000555557771913 in catch_command_errors (command=0x5555580e55ad <execute_command(char const*, int)>, arg=0x7fffffffe017 "file aarch64-mte-gcore", from_tty=1, do_bp_actions=true) at /home/simark/src/binutils-gdb/gdb/main.c:513
    #11 0x0000555557771fba in execute_cmdargs (cmdarg_vec=0x7fffffffd570, file_type=CMDARG_FILE, cmd_type=CMDARG_COMMAND, ret=0x7fffffffd230) at /home/simark/src/binutils-gdb/gdb/main.c:608
    #12 0x00005555577755ac in captured_main_1 (context=0x7fffffffda10) at /home/simark/src/binutils-gdb/gdb/main.c:1299
    #13 0x0000555557775c2d in captured_main (data=0x7fffffffda10) at /home/simark/src/binutils-gdb/gdb/main.c:1320
    #14 0x0000555557775cc2 in gdb_main (args=0x7fffffffda10) at /home/simark/src/binutils-gdb/gdb/main.c:1345
    #15 0x00005555568bdcbe in main (argc=10, argv=0x7fffffffdba8) at /home/simark/src/binutils-gdb/gdb/gdb.c:32

Here, target_auxv_search is called on the inferior's target stack.  The
target stack only contains the exec target, so the query returns empty
auxv data.  This gets cached for that inferior in `auxv_inferior_data`.

In its constructor (before it is pushed to the inferior's target stack),
the core_target needs to identify the right target description from the
core, and for that asks the gdbarch to read a target description from
the core file.  Because some implementations of
gdbarch_core_read_description (such as AArch64's) need to read auxv data
from the core in order to determine the right target description, the
core_target passes a pointer to itself, allowing implementations to call
target_auxv_search it.  However, because we have previously cached
(empty) auxv data for that inferior, target_auxv_search searched that
cached (empty) auxv data, not auxv data read from the core.  Remember
that this data was obtained by reading auxv on the inferior's target
stack, which only contained an exec target.

The problem I see is that while target_auxv_search offers the
flexibility of reading from an arbitrary (passed as an argument) target,
the caching doesn't do the distinction of which target is being queried,
and where the cached data came from.  So, you could read auxv from a
target A, it gets cached, then you try to read auxv from a target B, and
it returns the cached data from target A.  That sounds wrong.  In our
case, we expect to read different auxv data from the core target than
what we have read from the target stack earlier, so it doesn't make
sense to hit the cache in this case.

To fix this, I propose splitting the code paths that read auxv data from
an inferior's target stack and those that read from a passed-in target.
The code path that reads from the target stack will keep caching,
whereas the one that reads from a passed-in target won't.  And since,
searching in auxv data is independent from where this data came from,
split the "read" part from the "search" part.

From what I understand, auxv caching was introduced mostly to reduce
latency on remote connections, when doing many queries.  With the change
I propose, only the queries done while constructing the core_target
end up not using cached auxv data.  This is fine, because there are just
a handful of queries max, done at this point, and reading core files is
local.

The changes to auxv functions are:

 - Introduce 2 target_read_auxv functions.  One reads from an explicit
   target_ops and doesn't do caching (to be used in
   gdbarch_core_read_description context).  The other takes no argument,
   reads from the current inferior's target stack (it looks just like a
   standard target function wrapper) and does caching.

   The first target_read_auxv actually replaces get_auxv_inferior_data,
   since it became a trivial wrapper around it.

 - Change the existing target_auxv_search to not read auxv data from the
   target, but to accept it as a parameter (a gdb::byte_vector).  This
   function doesn't care where the data came from, it just searches in
   it.  It still needs to take a target_ops and gdbarch to know how to
   parse auxv entries.

 - Add a convenience target_auxv_search overload that reads auxv
   data from the inferior's target stack and searches in it.  This
   overload is useful to replace the exist target_auxv_search calls that
   passed the `current_inferior ()->top_target ()` target and keep the
   call sites short.

 - Modify parse_auxv to accept a target_ops and gdbarch to use for
   parsing entries.  Not strictly related to the rest of this change,
   but it seems like a good change in the context.

Changes in architecture-specific files (tdep and nat):

 - In linux-tdep, linux_get_hwcap and linux_get_hwcap2 get split in two,
   similar to target_auxv_search.  One version receives auxv data,
   target and arch as parameters.  The other gets everything from the
   current inferior.  The latter is for convenience, to avoid making
   call sites too ugly.

 - Call sites of linux_get_hwcap and linux_get_hwcap2 are adjusted to
   use either of the new versions.  The call sites in
   gdbarch_core_read_description context explicitly read auxv data from
   the passed-in target and call the linux_get_hwcap{,2} function with
   parameters.  Other call sites use the versions without parameters.

 - Same idea for arm_fbsd_read_description_auxv.

 - Call sites of target_auxv_search that passed
   `current_inferior ()->top_target ()` are changed to use the
   target_auxv_search overload that works in the current inferior.

Change-Id: Ib775a220cf1e76443fb7da2fdff8fc631128fe66
---
 gdb/aarch64-linux-nat.c  |  6 +--
 gdb/aarch64-linux-tdep.c |  6 ++-
 gdb/arm-fbsd-nat.c       |  2 +-
 gdb/arm-fbsd-tdep.c      | 25 ++++++++---
 gdb/arm-fbsd-tdep.h      | 12 ++++-
 gdb/arm-linux-nat.c      |  2 +-
 gdb/arm-linux-tdep.c     |  3 +-
 gdb/auxv.c               | 94 ++++++++++++++++++++++------------------
 gdb/auxv.h               | 22 +++++++++-
 gdb/elfread.c            |  2 +-
 gdb/fbsd-tdep.c          |  7 ++-
 gdb/linux-tdep.c         | 58 ++++++++++++++++++-------
 gdb/linux-tdep.h         | 26 ++++++++---
 gdb/ppc-linux-nat.c      | 19 +++-----
 gdb/ppc-linux-tdep.c     |  3 +-
 gdb/rs6000-tdep.c        |  3 +-
 gdb/s390-linux-nat.c     |  2 +-
 gdb/s390-linux-tdep.c    |  3 +-
 gdb/solib-svr4.c         | 15 +++----
 gdb/sparc64-tdep.c       |  6 +--
 20 files changed, 200 insertions(+), 116 deletions(-)

diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
index eda79ec6d35c..caefcb364852 100644
--- a/gdb/aarch64-linux-nat.c
+++ b/gdb/aarch64-linux-nat.c
@@ -781,8 +781,8 @@ aarch64_linux_nat_target::read_description ()
   if (ret == 0)
     return aarch32_read_description ();
 
-  CORE_ADDR hwcap = linux_get_hwcap (this);
-  CORE_ADDR hwcap2 = linux_get_hwcap2 (this);
+  CORE_ADDR hwcap = linux_get_hwcap ();
+  CORE_ADDR hwcap2 = linux_get_hwcap2 ();
 
   aarch64_features features;
   features.vq = aarch64_sve_get_vq (tid);
@@ -918,7 +918,7 @@ aarch64_linux_nat_target::thread_architecture (ptid_t ptid)
 bool
 aarch64_linux_nat_target::supports_memory_tagging ()
 {
-  return (linux_get_hwcap2 (this) & HWCAP2_MTE) != 0;
+  return (linux_get_hwcap2 () & HWCAP2_MTE) != 0;
 }
 
 /* Implement the "fetch_memtags" target_ops method.  */
diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 15773c75da83..9ce3569a277c 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -33,6 +33,7 @@
 #include "target.h"
 #include "target/target.h"
 #include "expop.h"
+#include "auxv.h"
 
 #include "regcache.h"
 #include "regset.h"
@@ -779,8 +780,9 @@ aarch64_linux_core_read_description (struct gdbarch *gdbarch,
 				     struct target_ops *target, bfd *abfd)
 {
   asection *tls = bfd_get_section_by_name (abfd, ".reg-aarch-tls");
-  CORE_ADDR hwcap = linux_get_hwcap (target);
-  CORE_ADDR hwcap2 = linux_get_hwcap2 (target);
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv (target);
+  CORE_ADDR hwcap = linux_get_hwcap (auxv, target, gdbarch);
+  CORE_ADDR hwcap2 = linux_get_hwcap2 (auxv, target, gdbarch);
 
   aarch64_features features;
   features.vq = aarch64_linux_core_read_vq (gdbarch, abfd);
diff --git a/gdb/arm-fbsd-nat.c b/gdb/arm-fbsd-nat.c
index b161b7ed9080..bbd722ed9230 100644
--- a/gdb/arm-fbsd-nat.c
+++ b/gdb/arm-fbsd-nat.c
@@ -122,7 +122,7 @@ arm_fbsd_nat_target::read_description ()
 #ifdef PT_GETREGSET
   tls = have_regset (inferior_ptid, NT_ARM_TLS) != 0;
 #endif
-  desc = arm_fbsd_read_description_auxv (this, tls);
+  desc = arm_fbsd_read_description_auxv (tls);
   if (desc == NULL)
     desc = this->beneath ()->read_description ();
   return desc;
diff --git a/gdb/arm-fbsd-tdep.c b/gdb/arm-fbsd-tdep.c
index 61c8f0cecad4..8944f7e9b758 100644
--- a/gdb/arm-fbsd-tdep.c
+++ b/gdb/arm-fbsd-tdep.c
@@ -190,15 +190,17 @@ arm_fbsd_iterate_over_regset_sections (struct gdbarch *gdbarch,
 	&arm_fbsd_vfpregset, "VFP floating-point", cb_data);
 }
 
-/* Lookup a target description from a target's AT_HWCAP auxiliary
-   vector.  */
+/* See arm-fbsd-tdep.h.  */
 
 const struct target_desc *
-arm_fbsd_read_description_auxv (struct target_ops *target, bool tls)
+arm_fbsd_read_description_auxv (const gdb::optional<gdb::byte_vector> &auxv,
+				target_ops *target, gdbarch *gdbarch, bool tls)
 {
   CORE_ADDR arm_hwcap = 0;
 
-  if (target_auxv_search (target, AT_FREEBSD_HWCAP, &arm_hwcap) != 1)
+  if (!auxv.has_value ()
+      || target_auxv_search (*auxv, target, gdbarch, AT_FREEBSD_HWCAP,
+			     &arm_hwcap) != 1)
     return arm_read_description (ARM_FP_TYPE_NONE, tls);
 
   if (arm_hwcap & HWCAP_VFP)
@@ -215,6 +217,18 @@ arm_fbsd_read_description_auxv (struct target_ops *target, bool tls)
   return arm_read_description (ARM_FP_TYPE_NONE, tls);
 }
 
+/* See arm-fbsd-tdep.h.  */
+
+const struct target_desc *
+arm_fbsd_read_description_auxv (bool tls)
+{
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv ();
+  return arm_fbsd_read_description_auxv (auxv,
+					 current_inferior ()->top_target (),
+					 current_inferior ()->gdbarch,
+					 tls);
+}
+
 /* Implement the "core_read_description" gdbarch method.  */
 
 static const struct target_desc *
@@ -224,7 +238,8 @@ arm_fbsd_core_read_description (struct gdbarch *gdbarch,
 {
   asection *tls = bfd_get_section_by_name (abfd, ".reg-aarch-tls");
 
-  return arm_fbsd_read_description_auxv (target, tls != nullptr);
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv (target);
+  return arm_fbsd_read_description_auxv (auxv, target, gdbarch, tls != nullptr);
 }
 
 /* Implement the get_thread_local_address gdbarch method.  */
diff --git a/gdb/arm-fbsd-tdep.h b/gdb/arm-fbsd-tdep.h
index 193eb76df3c9..85d7b59d1362 100644
--- a/gdb/arm-fbsd-tdep.h
+++ b/gdb/arm-fbsd-tdep.h
@@ -42,7 +42,17 @@ extern const struct regset arm_fbsd_vfpregset;
 #define	HWCAP_VFPv3		0x00002000
 #define	HWCAP_VFPD32		0x00080000
 
+/* Lookup a target description based on the AT_HWCAP value in the auxv data
+   AUXV.  */
+
+extern const struct target_desc *
+  arm_fbsd_read_description_auxv (const gdb::optional<gdb::byte_vector> &auxv,
+				  target_ops *target, gdbarch *gdbarch,
+				  bool tls);
+
+/* Same as the above, but read the auxv data from the current inferior.  */
+
 extern const struct target_desc *
-arm_fbsd_read_description_auxv (struct target_ops *target, bool tls);
+  arm_fbsd_read_description_auxv (bool tls);
 
 #endif /* ARM_FBSD_TDEP_H */
diff --git a/gdb/arm-linux-nat.c b/gdb/arm-linux-nat.c
index 0188c78fe7a0..a8b582fbef32 100644
--- a/gdb/arm-linux-nat.c
+++ b/gdb/arm-linux-nat.c
@@ -531,7 +531,7 @@ ps_get_thread_area (struct ps_prochandle *ph,
 const struct target_desc *
 arm_linux_nat_target::read_description ()
 {
-  CORE_ADDR arm_hwcap = linux_get_hwcap (this);
+  CORE_ADDR arm_hwcap = linux_get_hwcap ();
 
   if (have_ptrace_getregset == TRIBOOL_UNKNOWN)
     {
diff --git a/gdb/arm-linux-tdep.c b/gdb/arm-linux-tdep.c
index 1feb69fe6dd1..9db52de1a5f5 100644
--- a/gdb/arm-linux-tdep.c
+++ b/gdb/arm-linux-tdep.c
@@ -732,7 +732,8 @@ arm_linux_core_read_description (struct gdbarch *gdbarch,
 				 struct target_ops *target,
 				 bfd *abfd)
 {
-  CORE_ADDR arm_hwcap = linux_get_hwcap (target);
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv (target);
+  CORE_ADDR arm_hwcap = linux_get_hwcap (auxv, target, gdbarch);
 
   if (arm_hwcap & HWCAP_VFP)
     {
diff --git a/gdb/auxv.c b/gdb/auxv.c
index 76fc821c07c3..5853437b0f24 100644
--- a/gdb/auxv.c
+++ b/gdb/auxv.c
@@ -307,23 +307,21 @@ svr4_auxv_parse (struct gdbarch *gdbarch, const gdb_byte **readptr,
 
 /* Read one auxv entry from *READPTR, not reading locations >= ENDPTR.
 
-   Use the auxv_parse method from the current inferior's gdbarch, if defined,
-   else use the current inferior's target stack's auxv_parse.
+   Use the auxv_parse method from GDBARCH, if defined, else use the auxv_parse
+   method of OPS.
 
    Return 0 if *READPTR is already at the end of the buffer.
    Return -1 if there is insufficient buffer for a whole entry.
    Return 1 if an entry was read into *TYPEP and *VALP.  */
+
 static int
-parse_auxv (const gdb_byte **readptr, const gdb_byte *endptr, CORE_ADDR *typep,
-	    CORE_ADDR *valp)
+parse_auxv (target_ops *ops, gdbarch *gdbarch, const gdb_byte **readptr,
+	    const gdb_byte *endptr, CORE_ADDR *typep, CORE_ADDR *valp)
 {
-  struct gdbarch *gdbarch = target_gdbarch();
-
   if (gdbarch_auxv_parse_p (gdbarch))
     return gdbarch_auxv_parse (gdbarch, readptr, endptr, typep, valp);
 
-  return current_inferior ()->top_target ()->auxv_parse (readptr, endptr,
-							 typep, valp);
+  return ops->auxv_parse (readptr, endptr, typep, valp);
 }
 
 
@@ -354,45 +352,45 @@ invalidate_auxv_cache (void)
   invalidate_auxv_cache_inf (current_inferior ());
 }
 
-/* Fetch the auxv object from inferior INF.  If auxv is cached already,
-   return a pointer to the cache.  If not, fetch the auxv object from the
-   target and cache it.  This function always returns a valid INFO pointer.  */
+/* See auxv.h.  */
 
-static struct auxv_info *
-get_auxv_inferior_data (struct target_ops *ops)
+gdb::optional<gdb::byte_vector>
+target_read_auxv ()
 {
-  struct auxv_info *info;
-  struct inferior *inf = current_inferior ();
+  inferior *inf = current_inferior ();
+  auxv_info *info = auxv_inferior_data.get (inf);
 
-  info = auxv_inferior_data.get (inf);
-  if (info == NULL)
+  if (info == nullptr)
     {
       info = auxv_inferior_data.emplace (inf);
-      info->data = target_read_alloc (ops, TARGET_OBJECT_AUXV, NULL);
+      info->data = target_read_alloc (inf->top_target (), TARGET_OBJECT_AUXV,
+				      nullptr);
     }
 
-  return info;
+  return info->data;
 }
 
-/* Extract the auxiliary vector entry with a_type matching MATCH.
-   Return zero if no such entry was found, or -1 if there was
-   an error getting the information.  On success, return 1 after
-   storing the entry's value field in *VALP.  */
-int
-target_auxv_search (struct target_ops *ops, CORE_ADDR match, CORE_ADDR *valp)
+/* See auxv.h.  */
+
+gdb::optional<gdb::byte_vector>
+target_read_auxv (target_ops *ops)
 {
-  CORE_ADDR type, val;
-  auxv_info *info = get_auxv_inferior_data (ops);
+  return target_read_alloc (ops, TARGET_OBJECT_AUXV, NULL);
+}
 
-  if (!info->data)
-    return -1;
+/* See auxv.h.  */
 
-  const gdb_byte *data = info->data->data ();
+int
+target_auxv_search (const gdb::byte_vector &auxv, target_ops *ops,
+		    gdbarch *gdbarch, CORE_ADDR match, CORE_ADDR *valp)
+{
+  CORE_ADDR type, val;
+  const gdb_byte *data = auxv.data ();
   const gdb_byte *ptr = data;
-  size_t len = info->data->size ();
+  size_t len = auxv.size ();
 
   while (1)
-    switch (parse_auxv (&ptr, data + len, &type, &val))
+    switch (parse_auxv (ops, gdbarch, &ptr, data + len, &type, &val))
       {
       case 1:			/* Here's an entry, check it.  */
 	if (type == match)
@@ -406,10 +404,21 @@ target_auxv_search (struct target_ops *ops, CORE_ADDR match, CORE_ADDR *valp)
       default:			/* Bogosity.  */
 	return -1;
       }
-
-  /*NOTREACHED*/
 }
 
+/* See auxv.h.  */
+
+int
+target_auxv_search (CORE_ADDR match, CORE_ADDR *valp)
+{
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv ();
+
+  if (!auxv.has_value ())
+    return -1;
+
+  return target_auxv_search (*auxv, current_inferior ()->top_target (),
+			     current_inferior ()->gdbarch, match, valp);
+}
 
 /* Print the description of a single AUXV entry on the specified file.  */
 
@@ -551,21 +560,23 @@ default_print_auxv_entry (struct gdbarch *gdbarch, struct ui_file *file,
 /* Print the contents of the target's AUXV on the specified file.  */
 
 static int
-fprint_target_auxv (struct ui_file *file, struct target_ops *ops)
+fprint_target_auxv (struct ui_file *file)
 {
   struct gdbarch *gdbarch = target_gdbarch ();
   CORE_ADDR type, val;
   int ents = 0;
-  auxv_info *info = get_auxv_inferior_data (ops);
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv ();
 
-  if (!info->data)
+  if (!auxv.has_value ())
     return -1;
 
-  const gdb_byte *data = info->data->data ();
+  const gdb_byte *data = auxv->data ();
   const gdb_byte *ptr = data;
-  size_t len = info->data->size ();
+  size_t len = auxv->size ();
 
-  while (parse_auxv (&ptr, data + len, &type, &val) > 0)
+  while (parse_auxv (current_inferior ()->top_target (),
+		     current_inferior ()->gdbarch,
+		     &ptr, data + len, &type, &val) > 0)
     {
       gdbarch_print_auxv_entry (gdbarch, file, type, val);
       ++ents;
@@ -583,8 +594,7 @@ info_auxv_command (const char *cmd, int from_tty)
     error (_("The program has no auxiliary information now."));
   else
     {
-      int ents = fprint_target_auxv (gdb_stdout,
-				     current_inferior ()->top_target ());
+      int ents = fprint_target_auxv (gdb_stdout);
 
       if (ents < 0)
 	error (_("No auxiliary vector found, or failed reading it."));
diff --git a/gdb/auxv.h b/gdb/auxv.h
index ab2a5dee5f74..983e3bc9b0d9 100644
--- a/gdb/auxv.h
+++ b/gdb/auxv.h
@@ -46,13 +46,31 @@ extern int svr4_auxv_parse (struct gdbarch *gdbarch, const gdb_byte **readptr,
 			    const gdb_byte *endptr, CORE_ADDR *typep,
 			    CORE_ADDR *valp);
 
-/* Extract the auxiliary vector entry with a_type matching MATCH.
+/* Read auxv data from the current inferior's target stack.  */
+
+extern gdb::optional<gdb::byte_vector> target_read_auxv ();
+
+/* Read auxv data from OPS.  */
+
+extern gdb::optional<gdb::byte_vector> target_read_auxv (target_ops *ops);
+
+/* Search AUXV for an entry with a_type matching MATCH.
+
+   OPS and GDBARCH are the target and architecture to use to parse auxv entries.
+
    Return zero if no such entry was found, or -1 if there was
    an error getting the information.  On success, return 1 after
    storing the entry's value field in *VALP.  */
-extern int target_auxv_search (struct target_ops *ops,
+
+extern int target_auxv_search (const gdb::byte_vector &auxv,
+			       target_ops *ops, gdbarch *gdbarch,
 			       CORE_ADDR match, CORE_ADDR *valp);
 
+/* Same as the above, but read the auxv data from the current inferior.  Use
+   the current inferior's top target and arch to parse auxv entries.  */
+
+extern int target_auxv_search (CORE_ADDR match, CORE_ADDR *valp);
+
 /* Print a description of a single AUXV entry on the specified file.  */
 enum auxv_format { AUXV_FORMAT_DEC, AUXV_FORMAT_HEX, AUXV_FORMAT_STR };
 
diff --git a/gdb/elfread.c b/gdb/elfread.c
index 8aee634b44b5..1e8935302e8f 100644
--- a/gdb/elfread.c
+++ b/gdb/elfread.c
@@ -909,7 +909,7 @@ elf_gnu_ifunc_resolve_addr (struct gdbarch *gdbarch, CORE_ADDR pc)
      parameter.  FUNCTION is the function entry address.  ADDRESS may be a
      function descriptor.  */
 
-  target_auxv_search (current_inferior ()->top_target (), AT_HWCAP, &hwcap);
+  target_auxv_search (AT_HWCAP, &hwcap);
   hwcap_val = value_from_longest (builtin_type (gdbarch)
 				  ->builtin_unsigned_long, hwcap);
   address_val = call_function_by_hand (function, NULL, hwcap_val);
diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
index 309777c55f28..8431caf8f597 100644
--- a/gdb/fbsd-tdep.c
+++ b/gdb/fbsd-tdep.c
@@ -2308,9 +2308,7 @@ fbsd_vmmap_length (struct gdbarch *gdbarch, unsigned char *entries, size_t len,
 static bool
 fbsd_vdso_range (struct gdbarch *gdbarch, struct mem_range *range)
 {
-  struct target_ops *ops = current_inferior ()->top_target ();
-
-  if (target_auxv_search (ops, AT_FREEBSD_KPRELOAD, &range->start) <= 0)
+  if (target_auxv_search (AT_FREEBSD_KPRELOAD, &range->start) <= 0)
     return false;
 
   if (!target_has_execution ())
@@ -2337,7 +2335,8 @@ fbsd_vdso_range (struct gdbarch *gdbarch, struct mem_range *range)
     {
       /* Fetch the list of address space entries from the running target. */
       gdb::optional<gdb::byte_vector> buf =
-	target_read_alloc (ops, TARGET_OBJECT_FREEBSD_VMMAP, nullptr);
+	target_read_alloc (current_inferior ()->top_target (),
+			   TARGET_OBJECT_FREEBSD_VMMAP, nullptr);
       if (!buf || buf->empty ())
 	return false;
 
diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index adf518023bbe..dccb45d73a8d 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -417,10 +417,9 @@ int
 linux_is_uclinux (void)
 {
   CORE_ADDR dummy;
-  target_ops *target = current_inferior ()->top_target ();
 
-  return (target_auxv_search (target, AT_NULL, &dummy) > 0
-	  && target_auxv_search (target, AT_PAGESZ, &dummy) == 0);
+  return (target_auxv_search (AT_NULL, &dummy) > 0
+	  && target_auxv_search (AT_PAGESZ, &dummy) == 0);
 }
 
 static int
@@ -2379,8 +2378,7 @@ linux_vsyscall_range_raw (struct gdbarch *gdbarch, struct mem_range *range)
   char filename[100];
   long pid;
 
-  if (target_auxv_search (current_inferior ()->top_target (),
-			  AT_SYSINFO_EHDR, &range->start) <= 0)
+  if (target_auxv_search (AT_SYSINFO_EHDR, &range->start) <= 0)
     return 0;
 
   /* It doesn't make sense to access the host's /proc when debugging a
@@ -2570,8 +2568,7 @@ linux_displaced_step_location (struct gdbarch *gdbarch)
      local-store address and is thus not usable as displaced stepping
      location.  The auxiliary vector gets us the PowerPC-side entry
      point address instead.  */
-  if (target_auxv_search (current_inferior ()->top_target (),
-			  AT_ENTRY, &addr) <= 0)
+  if (target_auxv_search (AT_ENTRY, &addr) <= 0)
     throw_error (NOT_SUPPORTED_ERROR,
 		 _("Cannot find AT_ENTRY auxiliary vector entry."));
 
@@ -2658,13 +2655,15 @@ linux_displaced_step_restore_all_in_ptid (inferior *parent_inf, ptid_t ptid)
   per_inferior->disp_step_bufs->restore_in_ptid (ptid);
 }
 
-/* See linux-tdep.h.  */
+/* Helper for linux_get_hwcap and linux_get_hwcap2.  */
 
-CORE_ADDR
-linux_get_hwcap (struct target_ops *target)
+static CORE_ADDR
+linux_get_hwcap_helper (const gdb::optional<gdb::byte_vector> &auxv,
+			target_ops *target, gdbarch *gdbarch, CORE_ADDR match)
 {
   CORE_ADDR field;
-  if (target_auxv_search (target, AT_HWCAP, &field) != 1)
+  if (!auxv.has_value ()
+      || target_auxv_search (*auxv, target, gdbarch, match, &field) != 1)
     return 0;
   return field;
 }
@@ -2672,12 +2671,39 @@ linux_get_hwcap (struct target_ops *target)
 /* See linux-tdep.h.  */
 
 CORE_ADDR
-linux_get_hwcap2 (struct target_ops *target)
+linux_get_hwcap (const gdb::optional<gdb::byte_vector> &auxv,
+		 target_ops *target, gdbarch *gdbarch)
 {
-  CORE_ADDR field;
-  if (target_auxv_search (target, AT_HWCAP2, &field) != 1)
-    return 0;
-  return field;
+  return linux_get_hwcap_helper (auxv, target, gdbarch, AT_HWCAP);
+}
+
+/* See linux-tdep.h.  */
+
+CORE_ADDR
+linux_get_hwcap ()
+{
+  return linux_get_hwcap (target_read_auxv (),
+			  current_inferior ()->top_target (),
+			  current_inferior ()->gdbarch);
+}
+
+/* See linux-tdep.h.  */
+
+CORE_ADDR
+linux_get_hwcap2 (const gdb::optional<gdb::byte_vector> &auxv,
+		  target_ops *target, gdbarch *gdbarch)
+{
+  return linux_get_hwcap_helper (auxv, target, gdbarch, AT_HWCAP2);
+}
+
+/* See linux-tdep.h.  */
+
+CORE_ADDR
+linux_get_hwcap2 ()
+{
+  return linux_get_hwcap2 (target_read_auxv (),
+			   current_inferior ()->top_target (),
+			   current_inferior ()->gdbarch);
 }
 
 /* Display whether the gcore command is using the
diff --git a/gdb/linux-tdep.h b/gdb/linux-tdep.h
index bb907f2c8f35..95cc29c828c2 100644
--- a/gdb/linux-tdep.h
+++ b/gdb/linux-tdep.h
@@ -90,13 +90,27 @@ extern void linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch,
 
 extern int linux_is_uclinux (void);
 
-/* Fetch the AT_HWCAP entry from the auxv vector for the given TARGET.  On
-   error, 0 is returned.  */
-extern CORE_ADDR linux_get_hwcap (struct target_ops *target);
+/* Fetch the AT_HWCAP entry from auxv data AUXV.  Use TARGET and GDBARCH to
+   parse auxv entries.
 
-/* Fetch the AT_HWCAP2 entry from the auxv vector for the given TARGET.  On
-   error, 0 is returned.  */
-extern CORE_ADDR linux_get_hwcap2 (struct target_ops *target);
+   On error, 0 is returned.  */
+extern CORE_ADDR linux_get_hwcap (const gdb::optional<gdb::byte_vector> &auxv,
+				  struct target_ops *target, gdbarch *gdbarch);
+
+/* Same as the above, but obtain all the inputs from the current inferior.  */
+
+extern CORE_ADDR linux_get_hwcap ();
+
+/* Fetch the AT_HWCAP2 entry from auxv data AUXV.  Use TARGET and GDBARCH to
+   parse auxv entries.
+
+   On error, 0 is returned.  */
+extern CORE_ADDR linux_get_hwcap2 (const gdb::optional<gdb::byte_vector> &auxv,
+				   struct target_ops *target, gdbarch *gdbarch);
+
+/* Same as the above, but obtain all the inputs from the current inferior.  */
+
+extern CORE_ADDR linux_get_hwcap2 ();
 
 /* Fetch (and possibly build) an appropriate `struct link_map_offsets'
    for ILP32 and LP64 Linux systems.  */
diff --git a/gdb/ppc-linux-nat.c b/gdb/ppc-linux-nat.c
index dfa81e19a79f..795bb298955f 100644
--- a/gdb/ppc-linux-nat.c
+++ b/gdb/ppc-linux-nat.c
@@ -1965,8 +1965,8 @@ ppc_linux_nat_target::read_description ()
 
   features.wordsize = ppc_linux_target_wordsize (tid);
 
-  CORE_ADDR hwcap = linux_get_hwcap (current_inferior ()->top_target ());
-  CORE_ADDR hwcap2 = linux_get_hwcap2 (current_inferior ()->top_target ());
+  CORE_ADDR hwcap = linux_get_hwcap ();
+  CORE_ADDR hwcap2 = linux_get_hwcap2 ();
 
   if (have_ptrace_getsetvsxregs
       && (hwcap & PPC_FEATURE_HAS_VSX))
@@ -2123,8 +2123,7 @@ ppc_linux_nat_target::region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
 	 takes two hardware watchpoints though.  */
       if (len > 1
 	  && hwdebug_info.features & PPC_DEBUG_FEATURE_DATA_BP_RANGE
-	  && (linux_get_hwcap (current_inferior ()->top_target ())
-	      & PPC_FEATURE_BOOKE))
+	  && (linux_get_hwcap () & PPC_FEATURE_BOOKE))
 	return 2;
       /* Check if the processor provides DAWR interface.  */
       if (hwdebug_info.features & PPC_DEBUG_FEATURE_DATA_BP_DAWR)
@@ -2152,8 +2151,7 @@ ppc_linux_nat_target::region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
     {
       gdb_assert (m_dreg_interface.debugreg_p ());
 
-      if (((linux_get_hwcap (current_inferior ()->top_target ())
-	    & PPC_FEATURE_BOOKE)
+      if (((linux_get_hwcap () & PPC_FEATURE_BOOKE)
 	   && (addr + len) > (addr & ~3) + 4)
 	  || (addr + len) > (addr & ~7) + 8)
 	return 0;
@@ -2640,8 +2638,7 @@ ppc_linux_nat_target::insert_watchpoint (CORE_ADDR addr, int len,
       long wp_value;
       long read_mode, write_mode;
 
-      if (linux_get_hwcap (current_inferior ()->top_target ())
-	  & PPC_FEATURE_BOOKE)
+      if (linux_get_hwcap () & PPC_FEATURE_BOOKE)
 	{
 	  /* PowerPC 440 requires only the read/write flags to be passed
 	     to the kernel.  */
@@ -3014,11 +3011,9 @@ ppc_linux_nat_target::watchpoint_addr_within_range (CORE_ADDR addr,
   int mask;
 
   if (m_dreg_interface.hwdebug_p ()
-      && (linux_get_hwcap (current_inferior ()->top_target ())
-	  & PPC_FEATURE_BOOKE))
+      && (linux_get_hwcap () & PPC_FEATURE_BOOKE))
     return start <= addr && start + length >= addr;
-  else if (linux_get_hwcap (current_inferior ()->top_target ())
-	   & PPC_FEATURE_BOOKE)
+  else if (linux_get_hwcap () & PPC_FEATURE_BOOKE)
     mask = 3;
   else
     mask = 7;
diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 96eb931743fd..3bc972dfc9aa 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -1599,7 +1599,8 @@ ppc_linux_core_read_description (struct gdbarch *gdbarch,
   if (vsx)
     features.vsx = true;
 
-  CORE_ADDR hwcap = linux_get_hwcap (target);
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv (target);
+  CORE_ADDR hwcap = linux_get_hwcap (auxv, target, gdbarch);
 
   features.isa205 = ppc_linux_has_isa205 (hwcap);
 
diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index 2a396eff4c49..bbdc6f6e5555 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -5503,8 +5503,7 @@ ppc_process_record_op31 (struct gdbarch *gdbarch, struct regcache *regcache,
       return 0;
 
     case 1014:		/* Data Cache Block set to Zero */
-      if (target_auxv_search (current_inferior ()->top_target (),
-			      AT_DCACHEBSIZE, &at_dcsz) <= 0
+      if (target_auxv_search (AT_DCACHEBSIZE, &at_dcsz) <= 0
 	  || at_dcsz == 0)
 	at_dcsz = 128; /* Assume 128-byte cache line size (POWER8)  */
 
diff --git a/gdb/s390-linux-nat.c b/gdb/s390-linux-nat.c
index 2b21e0822362..96833e804e9a 100644
--- a/gdb/s390-linux-nat.c
+++ b/gdb/s390-linux-nat.c
@@ -1002,7 +1002,7 @@ s390_linux_nat_target::read_description ()
      that mode, report s390 architecture with 64-bit GPRs.  */
 #ifdef __s390x__
   {
-    CORE_ADDR hwcap = linux_get_hwcap (current_inferior ()->top_target ());
+    CORE_ADDR hwcap = linux_get_hwcap ();
 
     have_regset_tdb = (hwcap & HWCAP_S390_TE)
       && check_regset (tid, NT_S390_TDB, s390_sizeof_tdbregset);
diff --git a/gdb/s390-linux-tdep.c b/gdb/s390-linux-tdep.c
index 05bf03973fc3..b8f4362c0d9e 100644
--- a/gdb/s390-linux-tdep.c
+++ b/gdb/s390-linux-tdep.c
@@ -332,7 +332,8 @@ s390_core_read_description (struct gdbarch *gdbarch,
 			    struct target_ops *target, bfd *abfd)
 {
   asection *section = bfd_get_section_by_name (abfd, ".reg");
-  CORE_ADDR hwcap = linux_get_hwcap (target);
+  gdb::optional<gdb::byte_vector> auxv = target_read_auxv (target);
+  CORE_ADDR hwcap = linux_get_hwcap (auxv, target, gdbarch);
   bool high_gprs, v1, v2, te, vx, gs;
 
   if (!section)
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index a6a9ec5c86b3..db71cd31d33f 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -428,14 +428,11 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
   int pt_phdr_p = 0;
 
   /* Get required auxv elements from target.  */
-  if (target_auxv_search (current_inferior ()->top_target (),
-			  AT_PHDR, &at_phdr) <= 0)
+  if (target_auxv_search (AT_PHDR, &at_phdr) <= 0)
     return {};
-  if (target_auxv_search (current_inferior ()->top_target (),
-			  AT_PHENT, &at_phent) <= 0)
+  if (target_auxv_search (AT_PHENT, &at_phent) <= 0)
     return {};
-  if (target_auxv_search (current_inferior ()->top_target (),
-			  AT_PHNUM, &at_phnum) <= 0)
+  if (target_auxv_search (AT_PHNUM, &at_phnum) <= 0)
     return {};
   if (!at_phdr || !at_phnum)
     return {};
@@ -2250,8 +2247,7 @@ enable_break (struct svr4_info *info, int from_tty)
       /* If we were not able to find the base address of the loader
 	 from our so_list, then try using the AT_BASE auxilliary entry.  */
       if (!load_addr_found)
-	if (target_auxv_search (current_inferior ()->top_target (),
-				AT_BASE, &load_addr) > 0)
+	if (target_auxv_search (AT_BASE, &load_addr) > 0)
 	  {
 	    int addr_bit = gdbarch_addr_bit (target_gdbarch ());
 
@@ -2479,8 +2475,7 @@ svr4_exec_displacement (CORE_ADDR *displacementp)
   if ((bfd_get_file_flags (current_program_space->exec_bfd ()) & DYNAMIC) == 0)
     return 0;
 
-  if (target_auxv_search (current_inferior ()->top_target (),
-			  AT_ENTRY, &entry_point) <= 0)
+  if (target_auxv_search (AT_ENTRY, &entry_point) <= 0)
     return 0;
 
   exec_displacement
diff --git a/gdb/sparc64-tdep.c b/gdb/sparc64-tdep.c
index 6b9d9eaa9575..3122c62a1c38 100644
--- a/gdb/sparc64-tdep.c
+++ b/gdb/sparc64-tdep.c
@@ -214,12 +214,10 @@ adi_available (void)
     return proc->stat.is_avail;
 
   proc->stat.checked_avail = true;
-  if (target_auxv_search (current_inferior ()->top_target (),
-			  AT_ADI_BLKSZ, &value) <= 0)
+  if (target_auxv_search (AT_ADI_BLKSZ, &value) <= 0)
     return false;
   proc->stat.blksize = value;
-  target_auxv_search (current_inferior ()->top_target (),
-		      AT_ADI_NBITS, &value);
+  target_auxv_search (AT_ADI_NBITS, &value);
   proc->stat.nbits = value;
   proc->stat.max_version = (1 << proc->stat.nbits) - 2;
   proc->stat.is_avail = true;

base-commit: ae17d05a4a58baf42f297dfd40ed29256f4bc44d
-- 
2.37.3