Re: [PATCH 3/11] Add MIPS_MAX_REGISTER_SIZE (4/4)

Pedro Alves
2017-06-09T14:29:41Z

On 06/09/2017 02:23 PM, Maciej W. Rozycki wrote:

> Hardcoding things, and especially with literals, causes a maintenance
> pain when things change. Bad code elsewhere is not an excuse; besides,
> the other places where `8' is hardcoded are not (buffer) limits, but just
> handle specific register sizes, which are not going to change, and which
> are a completely different matter.

Perhaps you won't be surprised to learn that I subscribe to the same general
principles. However, I believe that this isn't, in fact, a completely
different matter, because the buffer in question is used to hold the
contents of a structure's address, to either put in a general register,
or in a stack slot, and those (addresses and general registers), unlike FPRs,
aren't expected to grow for a given architecture.

> So if you find `alloca' unacceptable,
> then the limit has to be a macro, and an assertion check is also due (as
> already proposed), preferably using `sizeof', so that a future change does
> not break it by accident.

I think a patch like the below is likely to clarify things.
(Builds, but is otherwise untested).

From 5bdf1c939d72bf2718a542164d99bb396f0526e3 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Fri, 9 Jun 2017 15:10:50 +0100
Subject: [PATCH] mips

---
gdb/mips-tdep.c | 38 ++++++++++++++++++++++----------------
1 file changed, 22 insertions(+), 16 deletions(-)

diff --git a/gdb/mips-tdep.c b/gdb/mips-tdep.c
index 82f91ba..7844c73 100644
--- a/gdb/mips-tdep.c
+++ b/gdb/mips-tdep.c
@@ -271,6 +271,9 @@ mips_isa_regsize (struct gdbarch *gdbarch)
/ gdbarch_bfd_arch_info (gdbarch)->bits_per_byte);
}

+/* Max saved register size. */
+#define MAX_MIPS_ABI_REGSIZE 8
+
/* Return the currently configured (or set) saved register size. */

unsigned int
@@ -4476,7 +4479,7 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
int stack_offset = 0;
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
CORE_ADDR func_addr = find_function_addr (function, NULL);
- int regsize = mips_abi_regsize (gdbarch);
+ int abi_regsize = mips_abi_regsize (gdbarch);

/* For shared libraries, "t9" needs to point at the function
address. */
@@ -4499,7 +4502,7 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
than necessary for EABI, because the first few arguments are
passed in registers, but that's OK. */
for (argnum = 0; argnum < nargs; argnum++)
- len += align_up (TYPE_LENGTH (value_type (args[argnum])), regsize);
+ len += align_up (TYPE_LENGTH (value_type (args[argnum])), abi_regsize);
sp -= align_up (len, 16);

if (mips_debug)
@@ -4528,7 +4531,9 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
for (argnum = 0; argnum < nargs; argnum++)
{
const gdb_byte *val;
- gdb_byte valbuf[MAX_REGISTER_SIZE];
+ /* This holds the address of structures that are passed by
+ reference. */
+ gdb_byte ref_valbuf[MAX_MIPS_ABI_REGISTER_SIZE];
struct value *arg = args[argnum];
struct type *arg_type = check_typedef (value_type (arg));
int len = TYPE_LENGTH (arg_type);
@@ -4541,13 +4546,14 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,

/* The EABI passes structures that do not fit in a register by
reference. */
- if (len > regsize
+ if (len > abi_regsize
&& (typecode == TYPE_CODE_STRUCT || typecode == TYPE_CODE_UNION))
{
- store_unsigned_integer (valbuf, regsize, byte_order,
+ gdb_assert (ARRAY_SIZE (ref_valbuf) >= abi_regsize);
+ store_unsigned_integer (ref_valbuf, abi_regsize, byte_order,
value_address (arg));
typecode = TYPE_CODE_PTR;
- len = regsize;
+ len = abi_regsize;
val = valbuf;
if (mips_debug)
fprintf_unfiltered (gdb_stdlog, " push");
@@ -4560,7 +4566,7 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
up before the check to see if there are any FP registers
left. Non MIPS_EABI targets also pass the FP in the integer
registers so also round up normal registers. */
- if (regsize < 8 && fp_register_arg_p (gdbarch, typecode, arg_type))
+ if (abi_regsize < 8 && fp_register_arg_p (gdbarch, typecode, arg_type))
{
if ((float_argreg & 1))
float_argreg++;
@@ -4626,12 +4632,12 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
/* Copy the argument to general registers or the stack in
register-sized pieces. Large arguments are split between
registers and stack. */
- /* Note: structs whose size is not a multiple of regsize
+ /* Note: structs whose size is not a multiple of abi_regsize
are treated specially: Irix cc passes
them in registers where gcc sometimes puts them on the
stack. For maximum compatibility, we will put them in
both places. */
- int odd_sized_struct = (len > regsize && len % regsize != 0);
+ int odd_sized_struct = (len > abi_regsize && len % abi_regsize != 0);

/* Note: Floating-point values that didn't fit into an FP
register are only written to memory. */
@@ -4639,7 +4645,7 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
{
/* Remember if the argument was written to the stack. */
int stack_used_p = 0;
- int partial_len = (len < regsize ? len : regsize);
+ int partial_len = (len < abi_regsize ? len : abi_regsize);

if (mips_debug)
fprintf_unfiltered (gdb_stdlog, " -- partial=%d",
@@ -4657,15 +4663,15 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
stack_used_p = 1;
if (gdbarch_byte_order (gdbarch) == BFD_ENDIAN_BIG)
{
- if (regsize == 8
+ if (abi_regsize == 8
&& (typecode == TYPE_CODE_INT
|| typecode == TYPE_CODE_PTR
|| typecode == TYPE_CODE_FLT) && len <= 4)
- longword_offset = regsize - len;
+ longword_offset = abi_regsize - len;
else if ((typecode == TYPE_CODE_STRUCT
|| typecode == TYPE_CODE_UNION)
- && TYPE_LENGTH (arg_type) < regsize)
- longword_offset = regsize - len;
+ && TYPE_LENGTH (arg_type) < abi_regsize)
+ longword_offset = abi_regsize - len;
}

if (mips_debug)
@@ -4706,7 +4712,7 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
if (mips_debug)
fprintf_filtered (gdb_stdlog, " - reg=%d val=%s",
argreg,
- phex (regval, regsize));
+ phex (regval, abi_regsize));
regcache_cooked_write_signed (regcache, argreg, regval);
argreg++;
}
@@ -4721,7 +4727,7 @@ mips_eabi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
only needs to be adjusted when it has been used. */

if (stack_used_p)
- stack_offset += align_up (partial_len, regsize);
+ stack_offset += align_up (partial_len, abi_regsize);
}
}
if (mips_debug)
--
2.5.5