GDBserver patch for x86 LynxOS-178

GDBserver patch for x86 LynxOS-178

[Joel Brobecker]

Hello,

As I hinted before, I have not been able to build GDBserver since
we switched over to C++, because I don't have a C++ compiler
for that target (I am not giving up yet, though).

So, if you are wondering why I am still submitting a GDBserver
patch for that target, it's because I have been working on x86
LynxOS-178 with GDBserver 7.10, and I think this one is a
straightforward cherry-pick, and will be useful if we manage
to port G++ and the libstdc++ to this target.

In the meantime, the patch was tested on x86-lynx18elf, with
a baseline based on GDB 7.10.

One element I did not explore was the idea of perhaps having
a specific target description xml for this platform, so as to not
show the registers that are not available on LynxOS-178.
In my opinion, it's only a nice-to-have, so I left it for some
other time. I'd like to finish the work on GDBserver for Windows,
for instance.

Thanks,
-- 
Joel

[RFA/gdbserver] x86 LynxOS-178: Adjust floating-point context structure

[Joel Brobecker]

The floating point context structure on x86 LynxOS-178 is not
the same as on LynxOS 5.x. As a consequence, trying to print
the return value of a function returning a float, for instance,
yields incorrect results.

This patch fixes the issue by providing an updated definition
for LynxOS-178 (the reason why we cannot access the actual definition
provided by the system still remains true).

gdb/gdbserver/ChangeLog:

        * lynx-i386-low.c (LYNXOS_178): New macro.
        (usr_fcontext_t) <LYNXOS_178>: Provide a definition that matches
        the layout on LynxOS-178.
        (lynx_i386_fill_fpregset, lynx_i386_store_fpregset): Do not
        handle floating point registers that are not supported by
        LynxOS-178.

OK to push to master?
-- 
Joel

---
 gdb/gdbserver/lynx-i386-low.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/gdb/gdbserver/lynx-i386-low.c b/gdb/gdbserver/lynx-i386-low.c
index c7b4fe4..25551db 100644
--- a/gdb/gdbserver/lynx-i386-low.c
+++ b/gdb/gdbserver/lynx-i386-low.c
@@ -24,7 +24,15 @@
 
 /* The following two typedefs are defined in a .h file which is not
    in the standard include path (/sys/include/family/x86/ucontext.h),
-   so we just duplicate them here.  */
+   so we just duplicate them here.
+
+   Unfortunately for us, the definition of this structure differs between
+   LynxOS 5.x and LynxOS 178.  Rather than duplicate the code, we use
+   different definitions depending on the target.  */
+
+#ifdef VMOS_DEV
+#define LYNXOS_178
+#endif
 
 /* General register context */
 typedef struct usr_econtext {
@@ -51,6 +59,28 @@ typedef struct usr_econtext {
     uint32_t    uec_gs;
 } usr_econtext_t;
 
+#if defined(LYNXOS_178)
+
+/* Floating point register context                                                                                      */
+typedef struct usr_fcontext {
+        uint32_t         ufc_control;
+        uint32_t         ufc_status;
+        uint32_t         ufc_tag;
+        uint8_t         *ufc_inst_off;
+        uint32_t         ufc_inst_sel;
+        uint8_t         *ufc_data_off;
+        uint32_t         ufc_data_sel;
+        struct ufp387_real {
+                uint16_t        umant4;
+        uint16_t        umant3;
+        uint16_t        umant2;
+        uint16_t        umant1;
+        uint16_t        us_and_e;
+        } ufc_reg[8];
+} usr_fcontext_t;
+
+#else /* This is LynxOS 5.x.  */
+
 /* Floating point and SIMD register context */
 typedef struct usr_fcontext {
         uint16_t         ufc_control;
@@ -86,6 +116,8 @@ typedef struct usr_fcontext {
         char ureserved[16][14];
 } usr_fcontext_t;
 
+#endif
+
 /* The index of various registers inside the regcache.  */
 
 enum lynx_i386_gdb_regnum
@@ -218,6 +250,7 @@ lynx_i386_fill_fpregset (struct regcache *regcache, char *buf)
                     buf + offsetof (usr_fcontext_t, ufc_data_sel));
   collect_register (regcache, I386_FOOFF_REGNUM,
                     buf + offsetof (usr_fcontext_t, ufc_data_off));
+#if !defined(LYNXOS_178)
   collect_16bit_register (regcache, I386_FOP_REGNUM,
                           buf + offsetof (usr_fcontext_t, ufc_opcode));
 
@@ -228,6 +261,7 @@ lynx_i386_fill_fpregset (struct regcache *regcache, char *buf)
 		      + i * sizeof (struct uxmm_register));
   collect_register (regcache, I386_MXCSR_REGNUM,
                     buf + offsetof (usr_fcontext_t, usse_mxcsr));
+#endif
 }
 
 /* This is the supply counterpart for collect_16bit_register:
@@ -276,6 +310,7 @@ lynx_i386_store_fpregset (struct regcache *regcache, const char *buf)
                    buf + offsetof (usr_fcontext_t, ufc_data_sel));
   supply_register (regcache, I386_FOOFF_REGNUM,
                    buf + offsetof (usr_fcontext_t, ufc_data_off));
+#if !defined(LYNXOS_178)
   supply_16bit_register (regcache, I386_FOP_REGNUM,
                          buf + offsetof (usr_fcontext_t, ufc_opcode));
 
@@ -286,6 +321,7 @@ lynx_i386_store_fpregset (struct regcache *regcache, const char *buf)
 		     + i * sizeof (struct uxmm_register));
   supply_register (regcache, I386_MXCSR_REGNUM,
                    buf + offsetof (usr_fcontext_t, usse_mxcsr));
+#endif
 }
 
 /* Implements the lynx_target_ops.arch_setup routine.  */
-- 
2.1.4

Re: [RFA/gdbserver] x86 LynxOS-178: Adjust floating-point context structure

[Simon Marchi]

On 2018-05-10 11:05, Joel Brobecker wrote:
> The floating point context structure on x86 LynxOS-178 is not
> the same as on LynxOS 5.x. As a consequence, trying to print
> the return value of a function returning a float, for instance,
> yields incorrect results.
> 
> This patch fixes the issue by providing an updated definition
> for LynxOS-178 (the reason why we cannot access the actual definition
> provided by the system still remains true).
> 
> gdb/gdbserver/ChangeLog:
> 
>         * lynx-i386-low.c (LYNXOS_178): New macro.
>         (usr_fcontext_t) <LYNXOS_178>: Provide a definition that 
> matches
>         the layout on LynxOS-178.

This syntax (with < >) is usually meant to denote fields (as if you were 
referring to field LYNXOS_178 in structure usr_fcontext_t).  To denote 
an #ifdef context (which is what I understand you want to do), I usually 
see this syntax:

   [LYNXOS_178] (usr_fcontext_t): ...

For example:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/ChangeLog-2017;h=aaadf142a4641ecd3feb26bc1dfa83dcc19e713c;hb=HEAD#l13806

>         (lynx_i386_fill_fpregset, lynx_i386_store_fpregset): Do not
>         handle floating point registers that are not supported by
>         LynxOS-178.
> 
> OK to push to master?

Otherwise, it looks good to me.

Simon

Re: [RFA/gdbserver] x86 LynxOS-178: Adjust floating-point context structure

[Joel Brobecker]

[-- Attachment #1: Type: text/plain, Size: 1409 bytes --]

> > gdb/gdbserver/ChangeLog:
> > 
> >         * lynx-i386-low.c (LYNXOS_178): New macro.
> >         (usr_fcontext_t) <LYNXOS_178>: Provide a definition that matches
> >         the layout on LynxOS-178.
> 
> This syntax (with < >) is usually meant to denote fields (as if you were
> referring to field LYNXOS_178 in structure usr_fcontext_t).  To denote an
> #ifdef context (which is what I understand you want to do), I usually see
> this syntax:
> 
>   [LYNXOS_178] (usr_fcontext_t): ...
> 
> For example:
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/ChangeLog-2017;h=aaadf142a4641ecd3feb26bc1dfa83dcc19e713c;hb=HEAD#l13806

Grumpf. I keep getting confused over this. Of course, you are right,
and this is explained in the GCS.

> 
> >         (lynx_i386_fill_fpregset, lynx_i386_store_fpregset): Do not
> >         handle floating point registers that are not supported by
> >         LynxOS-178.
> > 
> > OK to push to master?
> 
> Otherwise, it looks good to me.

Thanks. Attached is the patch I ended up pushing to master.

gdb/gdbserver/ChangeLog:

        * lynx-i386-low.c (LYNXOS_178): New macro.
        [LYNXOS_178] (usr_fcontext_t): Provide a definition that matches
        the layout on LynxOS-178.
        (lynx_i386_fill_fpregset, lynx_i386_store_fpregset): Do not
        handle floating point registers that are not supported by
        LynxOS-178.

-- 
Joel

[-- Attachment #2: 0001-x86-LynxOS-178-Adjust-floating-point-context-structu.patch --]
[-- Type: text/x-diff, Size: 5098 bytes --]

From 55271bf969c2c09b98aecd97b36170fbf76c3fc4 Mon Sep 17 00:00:00 2001
From: Joel Brobecker <brobecker@adacore.com>
Date: Thu, 10 May 2018 12:01:39 -0500
Subject: [PATCH] x86 LynxOS-178: Adjust floating-point context structure

The floating point context structure on x86 LynxOS-178 is not
the same as on LynxOS 5.x. As a consequence, trying to print
the return value of a function returning a float, for instance,
yields incorrect results.

This patch fixes the issue by providing an updated definition
for LynxOS-178 (the reason why we cannot access the actual definition
provided by the system still remains true).

gdb/gdbserver/ChangeLog:

        * lynx-i386-low.c (LYNXOS_178): New macro.
        [LYNXOS_178] (usr_fcontext_t): Provide a definition that matches
        the layout on LynxOS-178.
        (lynx_i386_fill_fpregset, lynx_i386_store_fpregset): Do not
        handle floating point registers that are not supported by
        LynxOS-178.
---
 gdb/gdbserver/ChangeLog       |  9 +++++++++
 gdb/gdbserver/lynx-i386-low.c | 38 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 36915cf..5e7ea10 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,12 @@
+2018-05-10  Joel Brobecker  <brobecker@adacore.com>
+
+	* lynx-i386-low.c (LYNXOS_178): New macro.
+	[LYNXOS_178] (usr_fcontext_t): Provide a definition that matches
+	the layout on LynxOS-178.
+	(lynx_i386_fill_fpregset, lynx_i386_store_fpregset): Do not
+	handle floating point registers that are not supported by
+	LynxOS-178.
+
 2018-05-10  Tom Tromey  <tom@tromey.com>
 
 	* configure: Rebuild.
diff --git a/gdb/gdbserver/lynx-i386-low.c b/gdb/gdbserver/lynx-i386-low.c
index 37c0dc9..a8817b4 100644
--- a/gdb/gdbserver/lynx-i386-low.c
+++ b/gdb/gdbserver/lynx-i386-low.c
@@ -25,7 +25,15 @@
 
 /* The following two typedefs are defined in a .h file which is not
    in the standard include path (/sys/include/family/x86/ucontext.h),
-   so we just duplicate them here.  */
+   so we just duplicate them here.
+
+   Unfortunately for us, the definition of this structure differs between
+   LynxOS 5.x and LynxOS 178.  Rather than duplicate the code, we use
+   different definitions depending on the target.  */
+
+#ifdef VMOS_DEV
+#define LYNXOS_178
+#endif
 
 /* General register context */
 typedef struct usr_econtext {
@@ -52,6 +60,28 @@ typedef struct usr_econtext {
     uint32_t    uec_gs;
 } usr_econtext_t;
 
+#if defined(LYNXOS_178)
+
+/* Floating point register context                                                                                      */
+typedef struct usr_fcontext {
+        uint32_t         ufc_control;
+        uint32_t         ufc_status;
+        uint32_t         ufc_tag;
+        uint8_t         *ufc_inst_off;
+        uint32_t         ufc_inst_sel;
+        uint8_t         *ufc_data_off;
+        uint32_t         ufc_data_sel;
+        struct ufp387_real {
+                uint16_t        umant4;
+        uint16_t        umant3;
+        uint16_t        umant2;
+        uint16_t        umant1;
+        uint16_t        us_and_e;
+        } ufc_reg[8];
+} usr_fcontext_t;
+
+#else /* This is LynxOS 5.x.  */
+
 /* Floating point and SIMD register context */
 typedef struct usr_fcontext {
         uint16_t         ufc_control;
@@ -87,6 +117,8 @@ typedef struct usr_fcontext {
         char ureserved[16][14];
 } usr_fcontext_t;
 
+#endif
+
 /* The index of various registers inside the regcache.  */
 
 enum lynx_i386_gdb_regnum
@@ -219,6 +251,7 @@ lynx_i386_fill_fpregset (struct regcache *regcache, char *buf)
                     buf + offsetof (usr_fcontext_t, ufc_data_sel));
   collect_register (regcache, I386_FOOFF_REGNUM,
                     buf + offsetof (usr_fcontext_t, ufc_data_off));
+#if !defined(LYNXOS_178)
   collect_16bit_register (regcache, I386_FOP_REGNUM,
                           buf + offsetof (usr_fcontext_t, ufc_opcode));
 
@@ -229,6 +262,7 @@ lynx_i386_fill_fpregset (struct regcache *regcache, char *buf)
 		      + i * sizeof (struct uxmm_register));
   collect_register (regcache, I386_MXCSR_REGNUM,
                     buf + offsetof (usr_fcontext_t, usse_mxcsr));
+#endif
 }
 
 /* This is the supply counterpart for collect_16bit_register:
@@ -277,6 +311,7 @@ lynx_i386_store_fpregset (struct regcache *regcache, const char *buf)
                    buf + offsetof (usr_fcontext_t, ufc_data_sel));
   supply_register (regcache, I386_FOOFF_REGNUM,
                    buf + offsetof (usr_fcontext_t, ufc_data_off));
+#if !defined(LYNXOS_178)
   supply_16bit_register (regcache, I386_FOP_REGNUM,
                          buf + offsetof (usr_fcontext_t, ufc_opcode));
 
@@ -287,6 +322,7 @@ lynx_i386_store_fpregset (struct regcache *regcache, const char *buf)
 		     + i * sizeof (struct uxmm_register));
   supply_register (regcache, I386_MXCSR_REGNUM,
                    buf + offsetof (usr_fcontext_t, usse_mxcsr));
+#endif
 }
 
 /* Implements the lynx_target_ops.arch_setup routine.  */
-- 
2.1.4