Re: [PATCH/RFA] Update m68k function return value handling

Mark Kettenis
2004-05-03T21:56:23Z

From: Andreas Schwab <schwab@suse.de>
Date: Mon, 03 May 2004 23:21:04 +0200

Mark Kettenis <kettenis@chello.nl> writes:

> Anyway, are the Linux changes OK with you?

Thanks, they look OK. I have sucessfully built it natively on m68k-linux
and ran a few tests, no failures.

Thanks for testing it on m68k-linux. I noticed that I forgot about
including "floatformat.h" so I didn't update Makefile.in. Fixed with
the attached patch which is what I actually checked in.

Index: ChangeLog
from Mark Kettenis <kettenis@gnu.org>

* m68k-tdep.h (struct gdbarch_tdep): Add member
struct_value_regnum.
(m68k_svr4_init_abi): New prototype.
* m68k-tdep.c: Include "floatformat.h". Add comment about all the
different calling conventions.
(m68k_extract_return_value): Remove code dealing with single-field
structs.
(m68k_store_return_value): Remove code dealing with single-field
structs. Correctly store return values of 5, 6, 7 or 8 bytes.
(m68k_extract_struct_value_address): Remove function.
(m68k_svr4_extract_return_value,m68k_svr4_store_return_value)
(m68k_reg_struct_return_p, m68k_return_value)
(m68k_svr4_return_value): New functions.
(m68k_use_struct_convention): Remove function.
(m68k_push_dummy_call): Use new struct_value_regnum member of
`struct gdbarch_tdep' instead of hardcoded register number to
store STRUCT_ADDR.
(m68k_svr4_init_abi): New function.
(m68k_gdbarch_init): Don't set extract_return_value,
store_return_values, deprecated_extract_struct_value_address and
use_struct_convention. Set return_value instead. Initialize new
struct_value_regnum member of `struct gdbarch_tdep'.
* m68klinux-tdep.c: Update copyright year.
(m68k_linux_extract_return_value, m68k_linux_store_return_value)
(m68k_linux_extract_struct_value_address): Remove function.
(m68k_linux_init_abi): Don't set extract_return_value,
store_return_values, deprecated_extract_struct_value_address and
use_struct_convention. Call m68k_svr4_init_abi but override the
new struct_value_regnum member of `struct gdbarch_tdep'.
* Makefile.in (m68k-tdep.o): Update dependencies.

Index: Makefile.in
===================================================================
RCS file: /cvs/src/src/gdb/Makefile.in,v
retrieving revision 1.556
diff -u -p -r1.556 Makefile.in
--- Makefile.in 2 May 2004 10:14:01 -0000 1.556
+++ Makefile.in 3 May 2004 21:54:24 -0000
@@ -2032,10 +2032,10 @@ m68knbsd-nat.o: m68knbsd-nat.c $(defs_h)
m68knbsd-tdep.o: m68knbsd-tdep.c $(defs_h) $(gdbtypes_h) $(regcache_h)
m68k-stub.o: m68k-stub.c
m68k-tdep.o: m68k-tdep.c $(defs_h) $(dwarf2_frame_h) $(frame_h) \
- $(frame_base_h) $(frame_unwind_h) $(symtab_h) $(gdbcore_h) \
- $(value_h) $(gdb_string_h) $(gdb_assert_h) $(inferior_h) \
- $(regcache_h) $(arch_utils_h) $(osabi_h) $(dis_asm_h) $(m68k_tdep_h) \
- $(gregset_h)
+ $(frame_base_h) $(frame_unwind_h) $(floatformat_h) $(symtab_h)\
+ $(gdbcore_h) $(value_h) $(gdb_string_h) $(gdb_assert_h) \
+ $(inferior_h) $(regcache_h) $(arch_utils_h) $(osabi_h) $(dis_asm_h) \
+ $(m68k_tdep_h) $(gregset_h)
macrocmd.o: macrocmd.c $(defs_h) $(macrotab_h) $(macroexp_h) $(macroscope_h) \
$(command_h) $(gdbcmd_h)
macroexp.o: macroexp.c $(defs_h) $(gdb_obstack_h) $(bcache_h) $(macrotab_h) \
Index: m68k-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/m68k-tdep.c,v
retrieving revision 1.84
diff -u -p -r1.84 m68k-tdep.c
--- m68k-tdep.c 1 May 2004 15:10:15 -0000 1.84
+++ m68k-tdep.c 3 May 2004 21:54:24 -0000
@@ -25,6 +25,7 @@
#include "frame.h"
#include "frame-base.h"
#include "frame-unwind.h"
+#include "floatformat.h"
#include "symtab.h"
#include "gdbcore.h"
#include "value.h"
@@ -129,8 +130,36 @@ m68k_register_name (int regnum)
return register_names[regnum];
}
\f
-/* Extract from an array REGBUF containing the (raw) register state, a
- function return value of TYPE, and copy that, in virtual format,
+/* There is a fair number of calling conventions that are in somewhat
+ wide use. The 68000/08/10 don't support an FPU, not even as a
+ coprocessor. All function return values are stored in %d0/%d1.
+ Structures are returned in a static buffer, a pointer to which is
+ returned in %d0. This means that functions returning a structure
+ are not re-entrant. To avoid this problem some systems use a
+ convention where the caller passes a pointer to a buffer in %a1
+ where the return values is to be stored. This convention is the
+ default, and is implemented in the function m68k_return_value.
+
+ The 68020/030/040/060 do support an FPU, either as a coprocessor
+ (68881/2) or built-in (68040/68060). That's why System V release 4
+ (SVR4) instroduces a new calling convention specified by the SVR4
+ psABI. Integer values are returned in %d0/%d1, pointer return
+ values in %a0 and floating values in %fp0. When calling functions
+ returning a structure the caller should pass a pointer to a buffer
+ for the return value in %a0. This convention is implemented in the
+ function m68k_svr4_return_value, and by appropriately setting the
+ struct_value_regnum member of `struct gdbarch_tdep'.
+
+ GNU/Linux returns values in the same way as SVR4 does, but uses %a1
+ for passing the structure return value buffer.
+
+ GCC can also generate code where small structures are returned in
+ %d0/%d1 instead of in memory by using -freg-struct-return. This is
+ the default on NetBSD a.out, OpenBSD and GNU/Linux and several
+ embedded systems. This convention is implemented by setting the
+ struct_return member of `struct gdbarch_tdep' to reg_struct_return. */
+
+/* Read a function return value of TYPE from REGCACHE, and copy that
into VALBUF. */

static void
@@ -140,13 +169,6 @@ m68k_extract_return_value (struct type *
int len = TYPE_LENGTH (type);
char buf[M68K_MAX_REGISTER_SIZE];

- if (TYPE_CODE (type) == TYPE_CODE_STRUCT
- && TYPE_NFIELDS (type) == 1)
- {
- m68k_extract_return_value (TYPE_FIELD_TYPE (type, 0), regcache, valbuf);
- return;
- }
-
if (len <= 4)
{
regcache_raw_read (regcache, M68K_D0_REGNUM, buf);
@@ -164,29 +186,39 @@ m68k_extract_return_value (struct type *
"Cannot extract return value of %d bytes long.", len);
}

-/* Write into the appropriate registers a function return value stored
- in VALBUF of type TYPE, given in virtual format. */
-
static void
-m68k_store_return_value (struct type *type, struct regcache *regcache,
- const void *valbuf)
+m68k_svr4_extract_return_value (struct type *type, struct regcache *regcache,
+ void *valbuf)
{
int len = TYPE_LENGTH (type);
+ char buf[M68K_MAX_REGISTER_SIZE];

- if (TYPE_CODE (type) == TYPE_CODE_STRUCT
- && TYPE_NFIELDS (type) == 1)
+ if (TYPE_CODE (type) == TYPE_CODE_FLT)
{
- m68k_store_return_value (TYPE_FIELD_TYPE (type, 0), regcache, valbuf);
- return;
+ regcache_raw_read (regcache, M68K_FP0_REGNUM, buf);
+ convert_typed_floating (buf, builtin_type_m68881_ext, valbuf, type);
}
+ else if (TYPE_CODE (type) == TYPE_CODE_PTR && len == 4)
+ regcache_raw_read (regcache, M68K_A0_REGNUM, valbuf);
+ else
+ m68k_extract_return_value (type, regcache, valbuf);
+}
+
+/* Write a function return value of TYPE from VALBUF into REGCACHE. */
+
+static void
+m68k_store_return_value (struct type *type, struct regcache *regcache,
+ const void *valbuf)
+{
+ int len = TYPE_LENGTH (type);

if (len <= 4)
regcache_raw_write_part (regcache, M68K_D0_REGNUM, 4 - len, len, valbuf);
else if (len <= 8)
{
- regcache_raw_write_part (regcache, M68K_D1_REGNUM, 8 - len,
+ regcache_raw_write_part (regcache, M68K_D0_REGNUM, 8 - len,
len - 4, valbuf);
- regcache_raw_write (regcache, M68K_D0_REGNUM,
+ regcache_raw_write (regcache, M68K_D1_REGNUM,
(char *) valbuf + (len - 4));
}
else
@@ -194,29 +226,108 @@ m68k_store_return_value (struct type *ty
"Cannot store return value of %d bytes long.", len);
}

-/* Extract from REGCACHE, which contains the (raw) register state, the
- address in which a function should return its structure value, as a
- CORE_ADDR. */
-
-static CORE_ADDR
-m68k_extract_struct_value_address (struct regcache *regcache)
+static void
+m68k_svr4_store_return_value (struct type *type, struct regcache *regcache,
+ const void *valbuf)
{
- char buf[4];
+ int len = TYPE_LENGTH (type);

- regcache_cooked_read (regcache, M68K_D0_REGNUM, buf);
- return extract_unsigned_integer (buf, 4);
+ if (TYPE_CODE (type) == TYPE_CODE_FLT)
+ {
+ char buf[M68K_MAX_REGISTER_SIZE];
+ convert_typed_floating (valbuf, type, buf, builtin_type_m68881_ext);
+ regcache_raw_write (regcache, M68K_FP0_REGNUM, buf);
+ }
+ else if (TYPE_CODE (type) == TYPE_CODE_PTR && len == 4)
+ {
+ regcache_raw_write (regcache, M68K_A0_REGNUM, valbuf);
+ regcache_raw_write (regcache, M68K_D0_REGNUM, valbuf);
+ }
+ else
+ m68k_store_return_value (type, regcache, valbuf);
}

+/* Return non-zero if TYPE, which is assumed to be a structure or
+ union type, should be returned in registers for architecture
+ GDBARCH. */
+
static int
-m68k_use_struct_convention (int gcc_p, struct type *type)
+m68k_reg_struct_return_p (struct gdbarch *gdbarch, struct type *type)
+{
+ struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+ enum type_code code = TYPE_CODE (type);
+ int len = TYPE_LENGTH (type);
+
+ gdb_assert (code == TYPE_CODE_STRUCT || code == TYPE_CODE_UNION);
+
+ if (tdep->struct_return == pcc_struct_return)
+ return 0;
+
+ return (len == 1 || len == 2 || len == 4 || len == 8);
+}
+
+/* Determine, for architecture GDBARCH, how a return value of TYPE
+ should be returned. If it is supposed to be returned in registers,
+ and READBUF is non-zero, read the appropriate value from REGCACHE,
+ and copy it into READBUF. If WRITEBUF is non-zero, write the value
+ from WRITEBUF into REGCACHE. */
+
+static enum return_value_convention
+m68k_return_value (struct gdbarch *gdbarch, struct type *type,
+ struct regcache *regcache, void *readbuf,
+ const void *writebuf)
{
- enum struct_return struct_return;
+ enum type_code code = TYPE_CODE (type);

- struct_return = gdbarch_tdep (current_gdbarch)->struct_return;
- return generic_use_struct_convention (struct_return == reg_struct_return,
- type);
+ if ((code == TYPE_CODE_STRUCT || code == TYPE_CODE_UNION)
+ && !m68k_reg_struct_return_p (gdbarch, type))
+ return RETURN_VALUE_STRUCT_CONVENTION;
+
+ /* GCC returns a `long double' in memory. */
+ if (code == TYPE_CODE_FLT && TYPE_LENGTH (type) == 12)
+ return RETURN_VALUE_STRUCT_CONVENTION;
+
+ if (readbuf)
+ m68k_extract_return_value (type, regcache, readbuf);
+ if (writebuf)
+ m68k_store_return_value (type, regcache, writebuf);
+
+ return RETURN_VALUE_REGISTER_CONVENTION;
}

+static enum return_value_convention
+m68k_svr4_return_value (struct gdbarch *gdbarch, struct type *type,
+ struct regcache *regcache, void *readbuf,
+ const void *writebuf)
+{
+ enum type_code code = TYPE_CODE (type);
+
+ if ((code == TYPE_CODE_STRUCT || code == TYPE_CODE_UNION)
+ && !m68k_reg_struct_return_p (gdbarch, type))
+ return RETURN_VALUE_STRUCT_CONVENTION;
+
+ /* This special case is for structures consisting of a single
+ `float' or `double' member. These structures are returned in
+ %fp0. For these structures, we call ourselves recursively,
+ changing TYPE into the type of the first member of the structure.
+ Since that should work for all structures that have only one
+ member, we don't bother to check the member's type here. */
+ if (code == TYPE_CODE_STRUCT && TYPE_NFIELDS (type) == 1)
+ {
+ type = check_typedef (TYPE_FIELD_TYPE (type, 0));
+ return m68k_svr4_return_value (gdbarch, type, regcache,
+ readbuf, writebuf);
+ }
+
+ if (readbuf)
+ m68k_svr4_extract_return_value (type, regcache, readbuf);
+ if (writebuf)
+ m68k_svr4_store_return_value (type, regcache, writebuf);
+
+ return RETURN_VALUE_REGISTER_CONVENTION;
+}
+\f
+
/* A function that tells us whether the function invocation represented
by fi does not have a frame on the stack associated with it. If it
does not, FRAMELESS is set to 1, else 0. */
@@ -293,6 +404,7 @@ m68k_push_dummy_call (struct gdbarch *gd
struct value **args, CORE_ADDR sp, int struct_return,
CORE_ADDR struct_addr)
{
+ struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
char buf[4];
int i;

@@ -321,7 +433,7 @@ m68k_push_dummy_call (struct gdbarch *gd
if (struct_return)
{
store_unsigned_integer (buf, 4, struct_addr);
- regcache_cooked_write (regcache, M68K_A1_REGNUM, buf);
+ regcache_cooked_write (regcache, tdep->struct_value_regnum, buf);
}

/* Store return address. */
@@ -952,6 +1064,22 @@ m68k_get_longjmp_target (CORE_ADDR *pc)
*pc = extract_unsigned_integer (buf, TARGET_PTR_BIT / TARGET_CHAR_BIT);
return 1;
}
+\f
+
+/* System V Release 4 (SVR4). */
+
+void
+m68k_svr4_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
+{
+ struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+
+ /* SVR4 uses a different calling convention. */
+ set_gdbarch_return_value (gdbarch, m68k_svr4_return_value);
+
+ /* SVR4 uses %a0 instead of %a1. */
+ tdep->struct_value_regnum = M68K_A0_REGNUM;
+}
+\f

/* Function: m68k_gdbarch_init
Initializer function for the m68k gdbarch vector.
@@ -984,11 +1112,6 @@ m68k_gdbarch_init (struct gdbarch_info i
set_gdbarch_believe_pcc_promotion (gdbarch, 1);
set_gdbarch_decr_pc_after_break (gdbarch, 2);

- set_gdbarch_extract_return_value (gdbarch, m68k_extract_return_value);
- set_gdbarch_store_return_value (gdbarch, m68k_store_return_value);
- set_gdbarch_deprecated_extract_struct_value_address (gdbarch, m68k_extract_struct_value_address);
- set_gdbarch_use_struct_convention (gdbarch, m68k_use_struct_convention);
-
set_gdbarch_deprecated_frameless_function_invocation (gdbarch, m68k_frameless_function_invocation);
set_gdbarch_frame_args_skip (gdbarch, 8);

@@ -1002,6 +1125,7 @@ m68k_gdbarch_init (struct gdbarch_info i
set_gdbarch_fp0_regnum (gdbarch, M68K_FP0_REGNUM);

set_gdbarch_push_dummy_call (gdbarch, m68k_push_dummy_call);
+ set_gdbarch_return_value (gdbarch, m68k_return_value);

/* Disassembler. */
set_gdbarch_print_insn (gdbarch, print_insn_m68k);
@@ -1012,6 +1136,7 @@ m68k_gdbarch_init (struct gdbarch_info i
#else
tdep->jb_pc = -1;
#endif
+ tdep->struct_value_regnum = M68K_A1_REGNUM;
tdep->struct_return = pcc_struct_return;

/* Frame unwinder. */
Index: m68k-tdep.h
===================================================================
RCS file: /cvs/src/src/gdb/m68k-tdep.h,v
retrieving revision 1.7
diff -u -p -r1.7 m68k-tdep.h
--- m68k-tdep.h 1 May 2004 15:10:15 -0000 1.7
+++ m68k-tdep.h 3 May 2004 21:54:24 -0000
@@ -67,9 +67,17 @@ struct gdbarch_tdep
/* The size of each entry in the jump buffer. */
size_t jb_elt_size;

+ /* Register in which the address to store a structure value is
+ passed to a function. */
+ int struct_value_regnum;
+
/* Convention for returning structures. */
enum struct_return struct_return;
};
+
+/* Initialize a SVR4 architecture variant. */
+extern void m68k_svr4_init_abi (struct gdbarch_info, struct gdbarch *);
+\f

/* Functions exported from m68kbsd-tdep.c. */

Index: m68klinux-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/m68klinux-tdep.c,v
retrieving revision 1.11
diff -u -p -r1.11 m68klinux-tdep.c
--- m68klinux-tdep.c 1 May 2004 15:10:15 -0000 1.11
+++ m68klinux-tdep.c 3 May 2004 21:54:24 -0000
@@ -1,7 +1,7 @@
/* Motorola m68k target-dependent support for GNU/Linux.

- Copyright 1996, 1998, 2000, 2001, 2002, 2003 Free Software Foundation,
- Inc.
+ Copyright 1996, 1998, 2000, 2001, 2002, 2003, 2004
+ Free Software Foundation, Inc.

This file is part of GDB.

@@ -275,108 +275,6 @@ m68k_linux_sigtramp_frame_sniffer (struc
return NULL;
}

-/* Extract from an array REGBUF containing the (raw) register state, a
- function return value of TYPE, and copy that, in virtual format,
- into VALBUF. */
-
-static void
-m68k_linux_extract_return_value (struct type *type, struct regcache *regcache,
- void *valbuf)
-{
- int len = TYPE_LENGTH (type);
- char buf[M68K_MAX_REGISTER_SIZE];
-
- if (TYPE_CODE (type) == TYPE_CODE_STRUCT
- && TYPE_NFIELDS (type) == 1)
- {
- m68k_linux_extract_return_value (TYPE_FIELD_TYPE (type, 0), regcache,
- valbuf);
- return;
- }
-
- if (TYPE_CODE (type) == TYPE_CODE_FLT)
- {
- regcache_raw_read (regcache, M68K_FP0_REGNUM, buf);
- convert_typed_floating (buf, builtin_type_m68881_ext, valbuf, type);
- }
- else if (TYPE_CODE (type) == TYPE_CODE_PTR)
- regcache_raw_read (regcache, M68K_A0_REGNUM, valbuf);
- else
- {
- if (len <= 4)
- {
- regcache_raw_read (regcache, M68K_D0_REGNUM, buf);
- memcpy (valbuf, buf + (4 - len), len);
- }
- else if (len <= 8)
- {
- regcache_raw_read (regcache, M68K_D0_REGNUM, buf);
- memcpy (valbuf, buf + (8 - len), len - 4);
- regcache_raw_read (regcache, M68K_D1_REGNUM,
- (char *) valbuf + (len - 4));
- }
- else
- internal_error (__FILE__, __LINE__,
- "Cannot extract return value of %d bytes long.", len);
- }
-}
-
-/* Write into the appropriate registers a function return value stored
- in VALBUF of type TYPE, given in virtual format. */
-
-static void
-m68k_linux_store_return_value (struct type *type, struct regcache *regcache,
- const void *valbuf)
-{
- int len = TYPE_LENGTH (type);
-
- if (TYPE_CODE (type) == TYPE_CODE_STRUCT
- && TYPE_NFIELDS (type) == 1)
- {
- m68k_linux_store_return_value (TYPE_FIELD_TYPE (type, 0), regcache,
- valbuf);
- return;
- }
-
- if (TYPE_CODE (type) == TYPE_CODE_FLT)
- {
- char buf[M68K_MAX_REGISTER_SIZE];
- convert_typed_floating (valbuf, type, buf, builtin_type_m68881_ext);
- regcache_raw_write (regcache, M68K_FP0_REGNUM, buf);
- }
- else if (TYPE_CODE (type) == TYPE_CODE_PTR)
- regcache_raw_write (regcache, M68K_A0_REGNUM, valbuf);
- else
- {
- if (len <= 4)
- regcache_raw_write_part (regcache, M68K_D0_REGNUM,
- 4 - len, len, valbuf);
- else if (len <= 8)
- {
- regcache_raw_write_part (regcache, M68K_D1_REGNUM, 8 - len,
- len - 4, valbuf);
- regcache_raw_write (regcache, M68K_D0_REGNUM,
- (char *) valbuf + (len - 4));
- }
- else
- internal_error (__FILE__, __LINE__,
- "Cannot store return value of %d bytes long.", len);
- }
-}
-
-/* Extract from an array REGBUF containing the (raw) register state
- the address in which a function should return its structure value,
- as a CORE_ADDR. */
-
-static CORE_ADDR
-m68k_linux_extract_struct_value_address (struct regcache *regcache)
-{
- char buf[4];
-
- regcache_cooked_read (regcache, M68K_A0_REGNUM, buf);
- return extract_unsigned_integer (buf, 4);
-}
-
static void
m68k_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
@@ -384,11 +282,15 @@ m68k_linux_init_abi (struct gdbarch_info

tdep->jb_pc = M68K_LINUX_JB_PC;
tdep->jb_elt_size = M68K_LINUX_JB_ELEMENT_SIZE;
- tdep->struct_return = reg_struct_return;

- set_gdbarch_extract_return_value (gdbarch, m68k_linux_extract_return_value);
- set_gdbarch_store_return_value (gdbarch, m68k_linux_store_return_value);
- set_gdbarch_deprecated_extract_struct_value_address (gdbarch, m68k_linux_extract_struct_value_address);
+ /* GNU/Linux uses a calling convention that's similar to SVR4. It
+ returns integer values in %d0/%di, pointer values in %a0 and
+ floating values in %fp0, just like SVR4, but uses %a1 to pass the
+ address to store a structure value. It also returns small
+ structures in registers instead of memory. */
+ m68k_svr4_init_abi (info, gdbarch);
+ tdep->struct_value_regnum = M68K_A1_REGNUM;
+ tdep->struct_return = reg_struct_return;

frame_unwind_append_sniffer (gdbarch, m68k_linux_sigtramp_frame_sniffer);