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dwarf2out.c: Revise DWARF2 Abbreviation Glossary comments.

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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.

From-SVN: r39475
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Jeffrey Oldham 2001-02-06 04:59:51 +00:00 committed by Jeffrey D. Oldham
parent d6706c5103
commit a401107daf
2 changed files with 41 additions and 11 deletions
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@ -1,3 +1,9 @@
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.
2001-02-05 Chandrakala Chavva <cchavva@redhat.com>
* final.c: Move the declaration of profile_label_no to ...

46
gcc/dwarf2out.c
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@ -57,12 +57,12 @@ Boston, MA 02111-1307, USA. */
/* 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
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
@ -1283,10 +1283,34 @@ dw_cfa_location cfa_temp;
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 register used to calculate the DWARF2 canonical
frame address register and offset
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
@ -1307,9 +1331,9 @@ dw_cfa_location cfa_temp;
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.
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