gdbserver: pass osabi to GDB in more target descriptions

Problem Description
-------------------

On a Windows machine I built gdbserver, configured for the target
'x86_64-w64-mingw32', then on a GNU/Linux machine I built GDB with
support for all target (--enable-targets=all).

On the Windows machine I start gdbserver with a small test binary:

  $ gdbserver 192.168.129.25:54321 C:\some\directory\executable.exe

On the GNU/Linux machine I start GDB without the test binary, and
connect to gdbserver.

As I have not given GDB the test binary, my expectation is that GDB
would connect to gdbserver and then download the file over the remote
protocol, but instead I was presented with this message:

  (gdb) target remote 192.168.129.25:54321
  Remote debugging using 192.168.129.25:54321
  warning: C:\some\directory\executable.exe: No such file or directory.
  0x00007ffa3e1e1741 in ?? ()
  (gdb)

What I found is that if I told GDB where to find the binary, like
this:

  (gdb) file target:C:/some/directory/executable.exe
  A program is being debugged already.
  Are you sure you want to change the file? (y or n) y
  Reading C:/some/directory/executable.exe from remote target...
  warning: File transfers from remote targets can be slow. Use "set sysroot" to access files locally instead.
  Reading C:/some/directory/executable.exe from remote target...
  Reading symbols from target:C:/some/directory/executable.exe...
  (gdb)

then GDB would download the executable.

The Actual Issue
----------------

I tracked the problem down to exec_file_find (solib.c).  The remote
target was passing an absolute Windows filename (beginning with "C:/"
in this case), but in exec_file_find GDB was failing the
IS_TARGET_ABSOLUTE_PATH call, and so was treating the filename as
relative.

The IS_TARGET_ABSOLUTE_PATH call was failing because GDB thought that
the file system kind was "unix", and as the filename didn't start with
a "/" it assumed the filename was not absolute.

But I'm connecting to a Windows target and 'target-file-system-kind'
was set to "auto", so GDB should be figuring out that the target
file-system is "dos-based".

Looking in effective_target_file_system_kind (filesystem.c), we find
that the logic of "auto" is delegated to the current gdbarch.  However
in windows-tdep.c we see:

  set_gdbarch_has_dos_based_file_system (gdbarch, 1);

So if we are using a Windows gdbarch we should have "dos-based"
filesystems.  What this means is that after connecting to the remote
target GDB has selected the wrong gdbarch.

What's happening is that the target description sent back by the
remote target only includes the x86-64 registers.  There's no
information about which OS we're on.  As a consequence, GDB picks the
first x86-64 gdbarch which can handle the provided register set, which
happens to be a GNU/Linux gdbarch.

And indeed, there doesn't appear to be anywhere in gdbserver that sets
the osabi on the target descriptions. Some target descriptions do have
their osabi set when the description is created, e.g. in:

  gdb/arch/amd64.c	- Sets GNU/Linux osabi when appropriate.
  gdb/arch/i386.c	- Likewise.
  gdb/arch/tic6x.c	- Always set GNU/Linux osabi.

There are also some cases in gdb/features/*.c where the tdesc is set,
but these locations are only called from GDB, not from gdbserver.

This means that many target descriptions are created without an osabi,
gdbserver does nothing to fix this, and the description is returned to
GDB without an osabi included.  This leaves GDB having to guess what
the target osabi is, and in some cases, GDB can get this wrong.

Proposed Solution
-----------------

I propose to change init_target_desc so that it requires an gdb_osabi
to be passed in, this will then be used to set the target_desc osabi
field.

I believe that within gdbserver init_target_desc is called for every
target_desc, so this should mean that every target_desc has an
opportunity to set the osabi to something sane.

I did consider passing the osabi into the code which creates the
target_desc objects, but that would require updating far more code, as
each target has its own code for creating target descriptions.
The approach taken here requires minimal changes and forces every
user of init_target_desc to think about what the correct osabi is.

In some cases, e.g. amd64, where the osabi is already set when the
target_desc is created, the init_target_desc call will override the
current value, however, we should always be replacing it with the same
actual value.  i.e. if the target_desc is created with the osabi set
to GNU/Linux, then this should only happen when gdbserver is built for
GNU/Linux, in which case the init_target_desc should also be setting
the osabi to GNU/Linux.

The Tricky Bits
---------------

Some targets, like amd64, use a features based approach for creating
target_desc objects, there's a function in arch/amd64.c which creates
a target_desc, adds features too it, and returns the new target_desc.
This target_desc is then passed to an init_target_desc call within
gdbserver.  This is the easy case to handle.

Then there are other targets which instead have a fixed set of xml
files, each of which is converted into a .dat file, which is then used
to generate a .cc file, which is compiled into gdbserver.  The
generated .cc file creates the target_desc object and calls
init_target_desc on it.  In this case though the target description
that is sent to GDB isn't generated from the target_desc object, but
is instead the contents of the fixed xml file.  For this case the
osabi which we pass to init_target_desc should match the osabi that
exists in the fixed xml file.

Luckily, in the previous commit I copied the osabi information from
the fixed xml files into the .dat files.  So in this commit I have
extended regdat.sh to read the osabi from the .dat file and use it in
the generated init_target_desc call.

The problem with some of these .dat base targets is that their fixed
xml files don't currently contain any osabi information, and the file
names don't indicate that they are Linux only (despite them currently
only being used from gdbserver for Linux targets), so I don't
currently feel confident adding any osabi information to these files.
An example would be features/rs6000/powerpc-64.xml.  For now I've just
ignored these cases.  The init_target_desc will use GDB_OSABI_UNKNOWN
which is the default.  This means that for these targets nothing
changes from the current behaviour.  But many other targets do now
pass the osabi back.  Targets that do pass the osabi back are
improved with this commit.

Conclusion
----------

Now when I connect to the Windows remote the target description
returned includes the osabi name.  With this extra information GDB
selects the correct gdbarch object, which means that GDB understands
the target has a "dos-based" file-system.  With that correct GDB
understands that the filename it was given is absolute, and so fetches
the file from the remote as we'd like.

Reviewed-By: Kevin Buettner <kevinb@redhat.com>

diff --git a/gdb/regformats/regdat.sh b/gdb/regformats/regdat.sh
index 38464c65b067128c5baa46382eeccf3929591f3f..49aa02a466de62d398cd81489e92099708176cde 100755 (executable)
--- a/gdb/regformats/regdat.sh
+++ b/gdb/regformats/regdat.sh
@@ -105,7 +105,7 @@ EOF
 }
 
 
-exec > new-$2
+exec > new-$3
 copyright $1
 echo '#include "regdef.h"'
 echo '#include "tdesc.h"'
@@ -118,6 +118,7 @@ xmlarch=x
 xmlosabi=x
 expedite=x
 feature=x
+osabi=unknown
 exec < $1
 while do_read
 do
@@ -143,7 +144,7 @@ do
   elif test "${type}" = "xmlarch"; then
     xmlarch="${entry}"
     continue
-  elif test "${type}" = "osabi"; then
+  elif test "${type}" = "xmlosabi"; then
     xmlosabi="${entry}"
     continue
   elif test "${type}" = "expedite"; then
@@ -152,6 +153,9 @@ do
   elif test "${type}" = "feature"; then
     feature="${entry}"
     continue
+  elif test "${type}" = "osabi"; then
+    osabi="${entry}"
+    continue
   elif test "${name}" = x; then
     echo "$0: $1 does not specify \`\`name''." 1>&2
     exit 1
@@ -188,11 +192,13 @@ else
 fi
 echo
 
+osabi_enum=$(grep "${osabi}" "$2" | sed 's/.*(\([^,]\+\),.*/GDB_OSABI_\1/')
+
 cat <<EOF
   result->xmltarget = xmltarget_${name};
 #endif
 
-  init_target_desc (result, expedite_regs_${name});
+  init_target_desc (result, expedite_regs_${name}, ${osabi_enum});
 
   tdesc_${name} = result;
 }
@@ -200,4 +206,4 @@ EOF
 
 # close things off
 exec 1>&2
-mv -- "new-$2" "$2"
+mv -- "new-$3" "$3"

diff --git a/gdbserver/Makefile.in b/gdbserver/Makefile.in
index 6148ccf9121bf3df9f751a79009d7e42f5bd53c7..f555ff439c4785b96147bb4f1f0cde69ee7cad66 100644 (file)
--- a/gdbserver/Makefile.in
+++ b/gdbserver/Makefile.in
@@ -488,6 +488,7 @@ stamp-xml: $(XML_DIR)/feature_to_c.sh Makefile $(XML_FILES)
 MAKEOVERRIDES =
 
 regdat_sh = $(srcdir)/../gdb/regformats/regdat.sh
+osabi_def = $(srcdir)/../gdbsupport/osabi.def
 
 UST_CFLAGS = \
        $(ustinc) \
@@ -588,11 +589,11 @@ target/%.o: ../gdb/target/%.c
 # Rules for register format descriptions.  Suffix destination files with
 # -generated to identify and clean them easily.
 
-%-generated.cc: ../gdb/regformats/%.dat $(regdat_sh)
-       $(ECHO_REGDAT) $(SHELL) $(regdat_sh) $< $@
+%-generated.cc: ../gdb/regformats/%.dat $(osabi_def) $(regdat_sh)
+       $(ECHO_REGDAT) $(SHELL) $(regdat_sh) $< $(osabi_def) $@
 
-%-generated.cc: ../gdb/regformats/rs6000/%.dat $(regdat_sh)
-       $(ECHO_REGDAT) $(SHELL) $(regdat_sh) $< $@
+%-generated.cc: ../gdb/regformats/rs6000/%.dat $(osabi_def) $(regdat_sh)
+       $(ECHO_REGDAT) $(SHELL) $(regdat_sh) $< $(osabi_def) $@
 
 # Rule for gdbreplay.o.  This is the same as COMPILE, but includes common-defs.h
 # instead of server.h.

diff --git a/gdbserver/linux-aarch32-tdesc.cc b/gdbserver/linux-aarch32-tdesc.cc
index b8987752b9f8bab5e9a514f78ffcd0e9e843a1d5..441fe668e6a4a236b09a4dd22f45b172eb5f492c 100644 (file)
--- a/gdbserver/linux-aarch32-tdesc.cc
+++ b/gdbserver/linux-aarch32-tdesc.cc
@@ -34,7 +34,7 @@ aarch32_linux_read_description ()
       tdesc_aarch32 = aarch32_create_target_description (false);
 
       static const char *expedite_regs[] = { "r11", "sp", "pc", 0 };
-      init_target_desc (tdesc_aarch32, expedite_regs);
+      init_target_desc (tdesc_aarch32, expedite_regs, GDB_OSABI_LINUX);
     }
   return tdesc_aarch32;
 }

diff --git a/gdbserver/linux-aarch64-tdesc.cc b/gdbserver/linux-aarch64-tdesc.cc
index 31ec7854cc0bd1124ddb1c7954ee6f6964b2a134..39d5bccdce18aba294440e5ed73fc73582c5db71 100644 (file)
--- a/gdbserver/linux-aarch64-tdesc.cc
+++ b/gdbserver/linux-aarch64-tdesc.cc
@@ -67,7 +67,8 @@ aarch64_linux_read_description (const aarch64_features &features)
 
       expedited_registers.push_back (nullptr);
 
-      init_target_desc (tdesc, (const char **) expedited_registers.data ());
+      init_target_desc (tdesc, (const char **) expedited_registers.data (),
+                       GDB_OSABI_LINUX);
 
       tdesc_aarch64_map[features] = tdesc;
     }

diff --git a/gdbserver/linux-arc-low.cc b/gdbserver/linux-arc-low.cc
index 1bcaf6c3f91118fbe8262173a33d26b28038900d..16d8d5824aa2f075f9d7920d48d121ddcbb84466 100644 (file)
--- a/gdbserver/linux-arc-low.cc
+++ b/gdbserver/linux-arc-low.cc
@@ -114,7 +114,7 @@ arc_linux_read_description (void)
   target_desc_up tdesc = arc_create_target_description (features);
 
   static const char *expedite_regs[] = { "sp", "status32", nullptr };
-  init_target_desc (tdesc.get (), expedite_regs);
+  init_target_desc (tdesc.get (), expedite_regs, GDB_OSABI_LINUX);
 
   return tdesc.release ();
 }

diff --git a/gdbserver/linux-arm-tdesc.cc b/gdbserver/linux-arm-tdesc.cc
index 559f9b0f3dc34fca09e64dede98d90784ac830a9..fff2e948f81f4b40e4cfec86e7ad07bf2a1d5199 100644 (file)
--- a/gdbserver/linux-arm-tdesc.cc
+++ b/gdbserver/linux-arm-tdesc.cc
@@ -37,7 +37,7 @@ arm_linux_read_description (arm_fp_type fp_type)
       tdesc = arm_create_target_description (fp_type, false);
 
       static const char *expedite_regs[] = { "r11", "sp", "pc", 0 };
-      init_target_desc (tdesc, expedite_regs);
+      init_target_desc (tdesc, expedite_regs, GDB_OSABI_LINUX);
 
       tdesc_arm_list[fp_type] = tdesc;
     }

diff --git a/gdbserver/linux-csky-low.cc b/gdbserver/linux-csky-low.cc
index 2eb5a2df17b9e6a5c58dcca714716b74cb5cd077..18a0d152b5ae9b27446675d37c2123b8e7169bc6 100644 (file)
--- a/gdbserver/linux-csky-low.cc
+++ b/gdbserver/linux-csky-low.cc
@@ -133,7 +133,7 @@ csky_target::low_arch_setup ()
 
   if (tdesc->expedite_regs.empty ())
     {
-      init_target_desc (tdesc.get (), expedite_regs);
+      init_target_desc (tdesc.get (), expedite_regs, GDB_OSABI_LINUX);
       gdb_assert (!tdesc->expedite_regs.empty ());
     }
 

diff --git a/gdbserver/linux-loongarch-low.cc b/gdbserver/linux-loongarch-low.cc
index 584ea64a7d95a4391758e850140274b05b0ef39c..cf7d6c0743cb16a2f032d418eb2600cb4cb48ed9 100644 (file)
--- a/gdbserver/linux-loongarch-low.cc
+++ b/gdbserver/linux-loongarch-low.cc
@@ -85,7 +85,7 @@ loongarch_target::low_arch_setup ()
 
   if (tdesc->expedite_regs.empty ())
     {
-      init_target_desc (tdesc.get (), expedite_regs);
+      init_target_desc (tdesc.get (), expedite_regs, GDB_OSABI_LINUX);
       gdb_assert (!tdesc->expedite_regs.empty ());
     }
   current_process ()->tdesc = tdesc.release ();

diff --git a/gdbserver/linux-riscv-low.cc b/gdbserver/linux-riscv-low.cc
index 999b82e24e18deda1c8d1551b049c24efb7b001e..44c805bb6d608c8880a5fb51064795c029a916ab 100644 (file)
--- a/gdbserver/linux-riscv-low.cc
+++ b/gdbserver/linux-riscv-low.cc
@@ -91,7 +91,7 @@ riscv_target::low_arch_setup ()
 
   if (tdesc->expedite_regs.empty ())
     {
-      init_target_desc (tdesc.get (), expedite_regs);
+      init_target_desc (tdesc.get (), expedite_regs, GDB_OSABI_LINUX);
       gdb_assert (!tdesc->expedite_regs.empty ());
     }
 

diff --git a/gdbserver/linux-x86-tdesc.cc b/gdbserver/linux-x86-tdesc.cc
index 13c80762605c658a4a6d0c1105eadf270cd7fb83..6aa5c4ab9705a7e6e7b1ef0a06cc7894536f6e77 100644 (file)
--- a/gdbserver/linux-x86-tdesc.cc
+++ b/gdbserver/linux-x86-tdesc.cc
@@ -26,10 +26,21 @@
 void
 x86_linux_post_init_tdesc (target_desc *tdesc, bool is_64bit)
 {
+  enum gdb_osabi osabi = GDB_OSABI_LINUX;
+
+#ifndef IN_PROCESS_AGENT
+  /* x86 target descriptions are created with the osabi already set.
+     However, init_target_desc requires us to override the already set
+     value.  That's fine, out new string should match the old one.  */
+  gdb_assert (tdesc_osabi_name (tdesc) != nullptr);
+  gdb_assert (strcmp (tdesc_osabi_name (tdesc),
+                     gdbarch_osabi_name (osabi)) == 0);
+#endif /* ! IN_PROCESS_AGENT */
+
 #ifdef __x86_64__
   if (is_64bit)
-    init_target_desc (tdesc, amd64_expedite_regs);
+    init_target_desc (tdesc, amd64_expedite_regs, osabi);
   else
 #endif
-    init_target_desc (tdesc, i386_expedite_regs);
+    init_target_desc (tdesc, i386_expedite_regs, osabi);
 }

diff --git a/gdbserver/netbsd-aarch64-low.cc b/gdbserver/netbsd-aarch64-low.cc
index f20a1a717733831e5af654fff108c79a784d7865..8834e0ad89406ea905cc4cd3af86134ec62b30b6 100644 (file)
--- a/gdbserver/netbsd-aarch64-low.cc
+++ b/gdbserver/netbsd-aarch64-low.cc
@@ -98,7 +98,7 @@ netbsd_aarch64_target::low_arch_setup ()
     = aarch64_create_target_description ({});
 
   static const char *expedite_regs_aarch64[] = { "x29", "sp", "pc", NULL };
-  init_target_desc (tdesc, expedite_regs_aarch64);
+  init_target_desc (tdesc, expedite_regs_aarch64, GDB_OSABI_NETBSD);
 
   current_process ()->tdesc = tdesc;
 }

diff --git a/gdbserver/netbsd-amd64-low.cc b/gdbserver/netbsd-amd64-low.cc
index b3f3aab5ec357876e0ea6b83d68bdaf0ef51fd52..ad7cb430b9208b625fdc705bd5159879df874b7f 100644 (file)
--- a/gdbserver/netbsd-amd64-low.cc
+++ b/gdbserver/netbsd-amd64-low.cc
@@ -193,7 +193,7 @@ netbsd_amd64_target::low_arch_setup ()
   target_desc *tdesc
     = amd64_create_target_description (X86_XSTATE_SSE_MASK, false, false, false);
 
-  init_target_desc (tdesc, amd64_expedite_regs);
+  init_target_desc (tdesc, amd64_expedite_regs, GDB_OSABI_NETBSD);
 
   current_process ()->tdesc = tdesc;
 }

diff --git a/gdbserver/netbsd-i386-low.cc b/gdbserver/netbsd-i386-low.cc
index 247a39797c41b267088a1798fe552ac6d886cdbc..ea6fce4c6f96728756bd15c8571c49f153e97f77 100644 (file)
--- a/gdbserver/netbsd-i386-low.cc
+++ b/gdbserver/netbsd-i386-low.cc
@@ -142,7 +142,7 @@ netbsd_i386_target::low_arch_setup ()
   target_desc *tdesc
     = i386_create_target_description (X86_XSTATE_SSE_MASK, false, false);
 
-  init_target_desc (tdesc, i386_expedite_regs);
+  init_target_desc (tdesc, i386_expedite_regs, GDB_OSABI_NETBSD);
 
   current_process ()->tdesc = tdesc;
 }

diff --git a/gdbserver/tdesc.cc b/gdbserver/tdesc.cc
index d052f43c76e69c6f47f40e124b08866de3b2ba40..da1287abbbed5933bf8ceddd4aa5d7a70ad4d473 100644 (file)
--- a/gdbserver/tdesc.cc
+++ b/gdbserver/tdesc.cc
@@ -53,7 +53,8 @@ void target_desc::accept (tdesc_element_visitor &v) const
 
 void
 init_target_desc (struct target_desc *tdesc,
-                 const char **expedite_regs)
+                 const char **expedite_regs,
+                 enum gdb_osabi osabi)
 {
   int offset = 0;
 
@@ -88,6 +89,8 @@ init_target_desc (struct target_desc *tdesc,
   int expedite_count = 0;
   while (expedite_regs[expedite_count] != nullptr)
     tdesc->expedite_regs.push_back (expedite_regs[expedite_count++]);
+
+  set_tdesc_osabi (tdesc, osabi);
 #endif
 }
 

diff --git a/gdbserver/tdesc.h b/gdbserver/tdesc.h
index 4796b50b4d137758ee36def867ec6530e04e8f2b..9264786de51173c262aadcaa31d205f0b274b7c4 100644 (file)
--- a/gdbserver/tdesc.h
+++ b/gdbserver/tdesc.h
@@ -20,6 +20,7 @@
 #define GDBSERVER_TDESC_H
 
 #include "gdbsupport/tdesc.h"
+#include "gdbsupport/osabi.h"
 
 #include "regdef.h"
 #include <vector>
@@ -81,10 +82,11 @@ void copy_target_description (struct target_desc *dest,
                              const struct target_desc *src);
 
 /* Initialize TDESC, and then set its expedite_regs field to
-   EXPEDITE_REGS.  */
+   EXPEDITE_REGS and its osabi to OSABI.  */
 
 void init_target_desc (struct target_desc *tdesc,
-                      const char **expedite_regs);
+                      const char **expedite_regs,
+                      enum gdb_osabi osabi);
 
 /* Return the current inferior's target description.  Never returns
    NULL.  */

diff --git a/gdbserver/win32-i386-low.cc b/gdbserver/win32-i386-low.cc
index af641200a052d15e36a1c3afc3a8bc1c70176f71..688e0123025984e7dc456fb12e66169ba461e3f9 100644 (file)
--- a/gdbserver/win32-i386-low.cc
+++ b/gdbserver/win32-i386-low.cc
@@ -596,12 +596,12 @@ i386_arch_setup (void)
 #ifdef __x86_64__
   tdesc = amd64_create_target_description (X86_XSTATE_SSE_MASK, false,
                                           false, false);
-  init_target_desc (tdesc, amd64_expedite_regs);
+  init_target_desc (tdesc, amd64_expedite_regs, WINDOWS_OSABI);
   win32_tdesc = tdesc;
 #endif
 
   tdesc = i386_create_target_description (X86_XSTATE_SSE_MASK, false, false);
-  init_target_desc (tdesc, i386_expedite_regs);
+  init_target_desc (tdesc, i386_expedite_regs, WINDOWS_OSABI);
 #ifdef __x86_64__
   wow64_win32_tdesc = tdesc;
 #else

diff --git a/gdbserver/win32-low.h b/gdbserver/win32-low.h
index ff997df0a66b351b0fe9a8fce5fc51d627e71bb2..daed16a6ae6a097ad4383c7ebe8b3cd3752b5eae 100644 (file)
--- a/gdbserver/win32-low.h
+++ b/gdbserver/win32-low.h
@@ -21,6 +21,7 @@
 
 #include <windows.h>
 #include "nat/windows-nat.h"
+#include "gdbsupport/osabi.h"
 
 struct target_desc;
 
@@ -31,6 +32,12 @@ extern const struct target_desc *win32_tdesc;
 extern const struct target_desc *wow64_win32_tdesc;
 #endif
 
+#ifdef __CYGWIN__
+constexpr enum gdb_osabi WINDOWS_OSABI = GDB_OSABI_CYGWIN;
+#else
+constexpr enum gdb_osabi WINDOWS_OSABI = GDB_OSABI_WINDOWS;
+#endif
+
 struct win32_target_ops
 {
   /* Architecture-specific setup.  */