From 6488583941b234e65b8d44aa1436fd871d6e16f2 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@polymtl.ca>
Date: Mon, 7 Apr 2025 13:51:59 -0400
Subject: gdb/testsuite/dwarf: add support to generate DWARF 5 split compile
 units

Add support to the DWARF assembler to generate DWARF 5 split compile
units.  The assembler knows how to generate DWARF < 5 split compile
units (fission), DWARF 5 compile units, but not DWARF 5 split compile
units.  What's missing is:

 - using the right unit type in the header: skeleton for the unit in the
   main file and split_compile for the unit in the DWO file
 - have a way for the caller to specify the DWO ID that will end up in
   the unit header

Add a dwo_id parameter to the cu proc.  In addition to specifying the
DWO ID, the presence of this parameter tells the assembler to use the
skeleton or split_compile unit type.

This is used in a subsequent patch.

Change-Id: I05d9b189a0843ea6c2771b1d5e5a91762426dea9
Approved-By: Tom Tromey <tom@tromey.com>
---
 gdb/testsuite/lib/dwarf.exp | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

(limited to 'gdb/testsuite/lib')

diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 943b80c..0a657f6 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -1441,6 +1441,17 @@ namespace eval Dwarf {
     #                default = default
     # fission 0|1  - boolean indicating if generating Fission debug info
     #                default = 0
+    # dwo_id       - The value to use as the dwo_id field of skeleton and
+    #                split_compile unit headers.  May only be used with DWARF
+    #                version 5.
+    #
+    #                If a dwo_id value is specified (is non-zero), this unit is
+    #                assumed to be part of a skeleton/split_unit pair.  The unit
+    #                type will be chosen according to the `fission` value.
+    #
+    #                When using DWARF version 5 and fission is non-zero, it is
+    #                mandatory to provide a non-zero dwo_id value.
+    #                default = 0
     # label <label>
     #              - string indicating label to be defined at the start
     #                of the CU header.
@@ -1463,6 +1474,7 @@ namespace eval Dwarf {
 	set _cu_version 4
 	set _cu_addr_size default
 	set _cu_is_fission 0
+	set dwo_id 0
 	set section ".debug_info"
 	set _abbrev_section ".debug_abbrev"
 	set label ""
@@ -1474,6 +1486,7 @@ namespace eval Dwarf {
 		version { set _cu_version $value }
 		addr_size { set _cu_addr_size $value }
 		fission { set _cu_is_fission $value }
+		dwo_id { set dwo_id $value }
 		label { set label $value }
 		default { error "unknown option $name" }
 	    }
@@ -1524,12 +1537,42 @@ namespace eval Dwarf {
 
 	# The CU header for DWARF 4 and 5 are slightly different.
 	if { $_cu_version == 5 } {
-	    _op .byte 0x1 "DW_UT_compile"
+	    # The presence of a DWO_ID indicates that we generate a skeleton
+	    # or split_compile unit.
+	    if { $dwo_id != 0 } {
+		if { $_cu_is_fission } {
+		    set unit_type_name "DW_UT_split_compile"
+		} else {
+		    set unit_type_name "DW_UT_skeleton"
+		}
+	    } else {
+		set unit_type_name "DW_UT_compile"
+	    }
+
+	    _op .byte $_constants($unit_type_name) $unit_type_name
 	    _op .byte $_cu_addr_size "Pointer size"
 	    _op_offset $_cu_offset_size $my_abbrevs Abbrevs
+
+	    # Output DWO ID, if specified.
+	    if { $dwo_id != 0 } {
+		_op .8byte $dwo_id "DWO_ID"
+	    } else {
+		# To help catch user errors: if the caller asked to put this
+		# unit in the DWO file but didn't provide a DWO ID, it is likely
+		# an error.
+		if { $_cu_is_fission } {
+		    error "DWO ID not specified for DWARF 5 split compile"
+		}
+	    }
 	} else {
 	    _op_offset $_cu_offset_size $my_abbrevs Abbrevs
 	    _op .byte $_cu_addr_size "Pointer size"
+
+	    # For DWARF versions < 5, the DWO ID is not in the unit header,
+	    # so it makes not sense to specify one.
+	    if { $dwo_id != 0 } {
+		error "DWO ID specified for DWARF < 5 unit"
+	    }
 	}
 
 	_defer_output $_abbrev_section {
-- 
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