From a401107daf176f8cbc5d05aade114d8b854054ba Mon Sep 17 00:00:00 2001 From: Jeffrey Oldham Date: Tue, 6 Feb 2001 04:59:51 +0000 Subject: [PATCH] dwarf2out.c: Revise DWARF2 Abbreviation Glossary comments. 2001-02-05 Jeffrey Oldham * dwarf2out.c: Revise DWARF2 Abbreviation Glossary comments. (dwarf2out_frame_debug_expr): Revise introductory comments to add a high-level description. From-SVN: r39475 --- gcc/ChangeLog | 6 ++++++ gcc/dwarf2out.c | 46 +++++++++++++++++++++++++++++++++++----------- 2 files changed, 41 insertions(+), 11 deletions(-) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 6d9d524d218..5b11f055c41 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +2001-02-05 Jeffrey Oldham + + * 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 * final.c: Move the declaration of profile_label_no to ... diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c index e424086a0c5..2ca66203a76 100644 --- a/gcc/dwarf2out.c +++ b/gcc/dwarf2out.c @@ -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 -- 2.30.2