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* values.c (value_as_address): If VAL is a function or method,

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just return its address; don't let COERCE_ARRAY convert its
address to a pointer, and then have unpack_long convert it back to
an address.
This commit is contained in:
Jim Blandy 2001-11-09 16:41:50 +00:00
parent e333d2c401
commit f312f05740
2 changed files with 49 additions and 0 deletions
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7
gdb/ChangeLog
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@ -1,3 +1,10 @@
2001-11-09 Jim Blandy <jimb@redhat.com>
* values.c (value_as_address): If VAL is a function or method,
just return its address; don't let COERCE_ARRAY convert its
address to a pointer, and then have unpack_long convert it back to
an address.
2001-11-06 Pierre Muller <muller@ics.u-strasbg.fr>
* p-lang.c (is_pascal_string_type): New function to determine if a

42
gdb/values.c
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@ -571,6 +571,48 @@ value_as_address (value_ptr val)
for pointers to char, in which the low bits *are* significant. */
return ADDR_BITS_REMOVE (value_as_long (val));
#else
/* There are several targets (IA-64, PowerPC, and others) which
don't represent pointers to functions as simply the address of
the function's entry point. For example, on the IA-64, a
function pointer points to a two-word descriptor, generated by
the linker, which contains the function's entry point, and the
value the IA-64 "global pointer" register should have --- to
support position-independent code. The linker generates
descriptors only for those functions whose addresses are taken.
On such targets, it's difficult for GDB to convert an arbitrary
function address into a function pointer; it has to either find
an existing descriptor for that function, or call malloc and
build its own. On some targets, it is impossible for GDB to
build a descriptor at all: the descriptor must contain a jump
instruction; data memory cannot be executed; and code memory
cannot be modified.
Upon entry to this function, if VAL is a value of type `function'
(that is, TYPE_CODE (VALUE_TYPE (val)) == TYPE_CODE_FUNC), then
VALUE_ADDRESS (val) is the address of the function. This is what
you'll get if you evaluate an expression like `main'. The call
to COERCE_ARRAY below actually does all the usual unary
conversions, which includes converting values of type `function'
to `pointer to function'. This is the challenging conversion
discussed above. Then, `unpack_long' will convert that pointer
back into an address.
So, suppose the user types `disassemble foo' on an architecture
with a strange function pointer representation, on which GDB
cannot build its own descriptors, and suppose further that `foo'
has no linker-built descriptor. The address->pointer conversion
will signal an error and prevent the command from running, even
though the next step would have been to convert the pointer
directly back into the same address.
The following shortcut avoids this whole mess. If VAL is a
function, just return its address directly. */
if (TYPE_CODE (VALUE_TYPE (val)) == TYPE_CODE_FUNC
|| TYPE_CODE (VALUE_TYPE (val)) == TYPE_CODE_METHOD)
return VALUE_ADDRESS (val);
COERCE_ARRAY (val);
/* Some architectures (e.g. Harvard), map instruction and data