PATCH: Revise dwarf2out.c's Comments
Jeffrey Oldham
oldham@codesourcery.com
Mon Feb 5 21:00:00 GMT 2001
Jason Merrill, Mark Mitchell, and I discussed recent comments added to
dwarf2out.c to assist users of dwarf2out_frame_debug_expr. We revised
them.
Thanks for Jason's and Mark's improvements. I am responsible for all
mistakes.
2001-02-05 Jeffrey Oldham <oldham@codesourcery.com>
* dwarf2out.c: Revise DWARF2 Abbreviation Glossary comments.
(dwarf2out_frame_debug_expr): Revise introductory comments to add
a high-level description.
Tested on i686-pc-linux-gnu by compiling dwarf2out.c
No source code was changed so no bootstrap or
regression test performed.
Approved by Mark Mitchell (mark@codesourcery.com)
Thanks,
Jeffrey D. Oldham
oldham@codesourcery.com
Index: dwarf2out.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/dwarf2out.c,v
retrieving revision 1.239
diff -c -p -r1.239 dwarf2out.c
*** dwarf2out.c 2001/02/04 22:43:58 1.239
--- dwarf2out.c 2001/02/06 03:48:46
*************** Boston, MA 02111-1307, USA. */
*** 57,68 ****
/* DWARF2 Abbreviation Glossary:
CFA = Canonical Frame Address
! stack address identifying a stack call frame; its value is
! the value of the stack pointer just before the call to the
! current function
! CFI = Canonical Frame Instruction
! information describing entries in a stack call frame, e.g.,
! CIE and FDE
CIE = Common Information Entry
information describing information common to one or more FDEs
DIE = Debugging Information Entry
--- 57,68 ----
/* DWARF2 Abbreviation Glossary:
CFA = Canonical Frame Address
! an abstract idea representing a fixed stack address
! identifying a stack call frame. The CFA register and
! offset, whose value may change, keeps track of its value at
! runtime.
! CFI = Call Frame Instruction
! an instruction for the DWARF2 abstract machine
CIE = Common Information Entry
information describing information common to one or more FDEs
DIE = Debugging Information Entry
*************** dw_cfa_location cfa_temp;
*** 1283,1292 ****
cfa, cfa_store, and cfa_temp.reg. We describe these rules so
users need not read the source code.
Invariants / Summaries of Rules
! cfa current register used to calculate the DWARF2 canonical
! frame address register and offset
cfa_store register used by prologue code to save things to the stack
cfa_store.offset is the offset from the value of
cfa_store.reg to the actual CFA
--- 1283,1316 ----
cfa, cfa_store, and cfa_temp.reg. We describe these rules so
users need not read the source code.
+ The High-Level Picture
+
+ Changes in the register we use to calculate the CFA: Currently we
+ assume that if you copy the CFA register into another register, we
+ should take the other one as the new CFA register; this seems to
+ work pretty well. If it's wrong for some target, it's simple
+ enough not to set RTX_FRAME_RELATED_P on the insn in question.
+
+ Changes in the register we use for saving registers to the stack:
+ This is usually SP, but not always. Again, we deduce that if you
+ copy SP into another register (and SP is not the CFA register),
+ then the new register is the one we will be using for register
+ saves. This also seems to work.
+
+ Register saves: There's not much guesswork about this one; if
+ RTX_FRAME_RELATED_P is set on an insn which modifies memory, it's a
+ register save, and the register used to calculate the destination
+ had better be the one we think we're using for this purpose.
+
+ Except: If the register being saved is the CFA register, and the
+ offset is non-zero, we are saving the CFA, so we assume we have to
+ use DW_CFA_def_cfa_expression. If the offset is 0, we assume that
+ the intent is to save the value of SP from the previous frame.
+
Invariants / Summaries of Rules
! cfa current rule for calculating the CFA. It usually
! consists of a register and an offset.
cfa_store register used by prologue code to save things to the stack
cfa_store.offset is the offset from the value of
cfa_store.reg to the actual CFA
*************** dw_cfa_location cfa_temp;
*** 1307,1315 ****
Rule 5: Create a new register cfa_store used to save items to the
stack.
! Rules 10-13: Save a register to the stack. Record the location in
! cfa_store.offset. Define offset as the difference of
! the original location and cfa_store's location.
The Rules
--- 1331,1339 ----
Rule 5: Create a new register cfa_store used to save items to the
stack.
! Rules 10-13: Save a register to the stack. Define offset as the
! difference of the original location and cfa_store's
! location.
The Rules
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