linux-kernel - [PATCH 3/7] kbuild: generate an address ranges map at vmlinux link time

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Message-Id: <20210709222523.17639-4-nick.alcock@oracle.com>
Date:   Fri,  9 Jul 2021 23:25:19 +0100
From:   Nick Alcock <nick.alcock@...cle.com>
To:     jeyu@...nel.org, masahiroy@...nel.org
Cc:     linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
        arnd@...db.de
Subject: [PATCH 3/7] kbuild: generate an address ranges map at vmlinux link time

This emits a new file, .tmp_vmlinux.ranges, which maps address
range/size pairs in vmlinux to the object files which make them up,
e.g., in part:

0x0000000000000000 0x30 arch/x86/kernel/cpu/common.o
0x0000000000001000 0x1000 arch/x86/events/intel/ds.o
0x0000000000002000 0x4000 arch/x86/kernel/irq_64.o
0x0000000000006000 0x5000 arch/x86/kernel/process.o
0x000000000000b000 0x1000 arch/x86/kernel/cpu/common.o
0x000000000000c000 0x5000 arch/x86/mm/cpu_entry_area.o
0x0000000000011000 0x10 arch/x86/kernel/espfix_64.o
0x0000000000011010 0x2 arch/x86/kernel/cpu/common.o
[...]

In my simple tests this seems to work with clang too, but if I'm not
sure how stable the format of clang's linker mapfiles is: if it turns
out not to work in some versions, the mapfile-massaging awk script added
here might need some adjustment.

Signed-off-by: Nick Alcock <nick.alcock@...cle.com>
---
 scripts/link-vmlinux.sh | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 0e0f6466b18d..00ad1b4b0055 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -178,6 +178,7 @@ vmlinux_link()
 			objects="--whole-archive		\
 				vmlinux.o 			\
 				--no-whole-archive		\
+				-Map=.tmp_vmlinux.map		\
 				${@}"
 		else
 			objects="--whole-archive		\
@@ -186,6 +187,7 @@ vmlinux_link()
 				--start-group			\
 				${KBUILD_VMLINUX_LIBS}		\
 				--end-group			\
+				-Map=.tmp_vmlinux.map		\
 				${@}"
 		fi
 
@@ -201,6 +203,7 @@ vmlinux_link()
 			-Wl,--start-group			\
 			${KBUILD_VMLINUX_LIBS}			\
 			-Wl,--end-group				\
+			-Wl,-Map=.tmp_vmlinux.map		\
 			${@}"
 
 		${CC} ${CFLAGS_vmlinux}				\
@@ -259,6 +262,19 @@ kallsyms()
 {
 	local kallsymopt;
 
+	# read the linker map to identify ranges of addresses:
+	#   - for each *.o file, report address, size, pathname
+	#       - most such lines will have four fields
+	#       - but sometimes there is a line break after the first field
+	#   - start reading at "Linker script and memory map"
+	#   - stop reading at ".brk"
+	${AWK} '
+	    /\.o$/ && start==1 { print $(NF-2), $(NF-1), $NF }
+	    /^Linker script and memory map/ { start = 1 }
+	    /^\.brk/ { exit(0) }
+	' .tmp_vmlinux.map | sort > .tmp_vmlinux.ranges
+
+	# get kallsyms options
 	if [ -n "${CONFIG_KALLSYMS_ALL}" ]; then
 		kallsymopt="${kallsymopt} --all-symbols"
 	fi
-- 
2.32.0.255.gd9b1d14a2a