This is the mail archive of the
gdb@sourceware.org
mailing list for the GDB project.
29 bits for dwarf2_per_cu_data.length ?
- From: dje at google dot com (Doug Evans)
- To: gdb at sourceware dot org
- Date: Sun, 28 Sep 2008 13:45:18 -0700 (PDT)
- Subject: 29 bits for dwarf2_per_cu_data.length ?
For my DW_FORM_sig8 work I've found a need to distinguish DW_TAG_type_unit
CUs (or TUs) from normal DW_TAG_compile_unit CUs in dwarf2_per_cu_data.
The easy way is to make length 29 bits.
struct dwarf2_per_cu_data
{
- /* The start offset and length of this compilation unit. 2**30-1
+ /* The start offset and length of this compilation unit. 2**29-1
bytes should suffice to store the length of any compilation unit
- if it doesn't, GDB will fall over anyway. */
unsigned long offset;
- unsigned long length : 30;
+ unsigned long length : 29;
+
+ /* Non-zero if this CU is from .debug_types.
+ Otherwise it's from .debug_info. */
+ unsigned long from_debug_types : 1;
That shrinks the maximum size of a CU from 1G to 512M.
I'm guessing it's a non-starter (although 512M for one CU is still a lot),
but before I try something else I thought I'd check.
OTOH, on 64 bit targets there is 32 bits of alignment padding
in dwarf2_per_cu_data. DIE's are a lot smaller these days, and there
are a whole lot more of them than CUs.
Can I spend a teensy bit of that gain and make dwarf2_per_cu_data 32 bits
bigger for 32-bit targets?
A related question: dwarf2_per_cu_data.offset is 64 bits on 64-bit
targets (unsigned long) and yet most other places only use 32 bits
(unsigned int). E.g., partial_die_info.offset.
Can I change everything to use an unsigned it?
E.g.,
diff -u -p -d -u -r1.284 dwarf2read.c
--- dwarf2read.c 23 Sep 2008 17:36:51 -0000 1.284
+++ dwarf2read.c 28 Sep 2008 20:34:50 -0000
@@ -358,15 +358,13 @@ struct dwarf2_cu
struct dwarf2_per_cu_data
{
- /* The start offset and length of this compilation unit. 2**30-1
- bytes should suffice to store the length of any compilation unit
- - if it doesn't, GDB will fall over anyway. */
- unsigned long offset;
- unsigned long length : 30;
+ /* The start offset and length of this compilation unit. */
+ unsigned int offset;
+ unsigned int length;
/* Flag indicating this compilation unit will be read in before
any of the current compilation units are processed. */
- unsigned long queued : 1;
+ unsigned int queued : 1;
/* This flag will be set if we need to load absolutely all DIEs
for this compilation unit, instead of just the ones we think
@@ -374,6 +372,10 @@ struct dwarf2_per_cu_data
hash table and don't find it. */
unsigned int load_all_dies : 1;
+ /* Non-zero if this CU is from .debug_types.
+ Otherwise it's from .debug_info. */
+ unsigned int from_debug_types : 1;
+
/* Set iff currently read in. */
struct dwarf2_cu *cu;