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Re: [patch] clarify ``struct type . length''
- To: Andrew Cagney <ac131313 at cygnus dot com>
- Subject: Re: [patch] clarify ``struct type . length''
- From: Jim Blandy <jimb at zwingli dot cygnus dot com>
- Date: 05 Sep 2001 17:46:04 -0500
- Cc: gdb-patches at sources dot redhat dot com
- References: <3B81A9BC.4010807@cygnus.com> <npheuhms9w.fsf@zwingli.cygnus.com>
I've committed this change. I hope it still addresses the issues you
had in mind with your original change.
2001-09-05 Jim Blandy <jimb@redhat.com>
* gdbtypes.h (struct type): Doc fix.
Index: gdbtypes.h
===================================================================
RCS file: /cvs/src/src/gdb/gdbtypes.h,v
retrieving revision 1.14
diff -c -c -b -F'^(' -r1.14 gdbtypes.h
*** gdbtypes.h 2001/08/24 04:46:43 1.14
--- gdbtypes.h 2001/09/05 22:42:33
***************
*** 231,251 ****
char *tag_name;
! /* Length of storage for a value of this type. This is of length
! of the type as defined by the debug info and not the length of
! the value that resides within the type. For instance, an
! i386-ext floating-point value only occupies 80 bits of what is
! typically a 12 byte `long double'. Various places pass this to
! memcpy and such, meaning it must be in units of HOST_CHAR_BIT.
! Various other places expect they can calculate addresses by
! adding it and such, meaning it must be in units of
! TARGET_CHAR_BIT. For some DSP targets, in which HOST_CHAR_BIT
! will (presumably) be 8 and TARGET_CHAR_BIT will be (say) 32,
! this is a problem. One fix would be to make this field in bits
! (requiring that it always be a multiple of HOST_CHAR_BIT and
! TARGET_CHAR_BIT)--the other choice would be to make it
! consistently in units of HOST_CHAR_BIT. */
unsigned length;
/* FIXME, these should probably be restricted to a Fortran-specific
--- 231,259 ----
char *tag_name;
! /* Length of storage for a value of this type. This is what
! sizeof(type) would return; use it for address arithmetic,
! memory reads and writes, etc. This size includes padding. For
! example, an i386 extended-precision floating point value really
! only occupies ten bytes, but most ABI's declare its size to be
! 12 bytes, to preserve alignment. A `struct type' representing
! such a floating-point type would have a `length' value of 12,
! even though the last two bytes are unused.
+ There's a bit of a host/target mess here, if you're concerned
+ about machines whose bytes aren't eight bits long, or who don't
+ have byte-addressed memory. Various places pass this to memcpy
+ and such, meaning it must be in units of host bytes. Various
+ other places expect they can calculate addresses by adding it
+ and such, meaning it must be in units of target bytes. For
+ some DSP targets, in which HOST_CHAR_BIT will (presumably) be 8
+ and TARGET_CHAR_BIT will be (say) 32, this is a problem.
+
+ One fix would be to make this field in bits (requiring that it
+ always be a multiple of HOST_CHAR_BIT and TARGET_CHAR_BIT) ---
+ the other choice would be to make it consistently in units of
+ HOST_CHAR_BIT. However, this would still fail to address
+ machines based on a ternary or decimal representation. */
unsigned length;
/* FIXME, these should probably be restricted to a Fortran-specific