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

[Joel Brobecker <brobecker@adacore.com>]

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> > 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

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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