linux-kernel - [PATCH v8 3/6] kbuild: generate an address ranges map at vmlinux link time

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Message-Id: <20220208184309.148192-4-nick.alcock@oracle.com>
Date:   Tue,  8 Feb 2022 18:43:06 +0000
From:   Nick Alcock <nick.alcock@...cle.com>
To:     mcgrof@...nel.org, masahiroy@...nel.org
Cc:     jolsa@...nel.org, rostedt@...dmis.org, bas@...lab.org,
        tglozar@...il.com, Ast-x64@...tonmail.com, viktor.malik@...il.com,
        dxu@...uu.xyz, acme@...nel.org, adrian.hunter@...el.com,
        ak@...ux.intel.com, irogers@...gle.com,
        linux-kbuild@...r.kernel.org, linux-modules@...r.kernel.org,
        linux-kernel@...r.kernel.org, arnd@...db.de,
        akpm@...ux-foundation.org, eugene.loh@...cle.com,
        kris.van.hees@...cle.com
Subject: [PATCH v8 3/6] 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>
Reviewed-by: Kris Van Hees <kris.van.hees@...cle.com>
---

Notes:
    v6: use ${wl} where appropriate to avoid failure on UML

 scripts/link-vmlinux.sh | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 666f7bbc13eb..981cd441ca21 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -203,7 +203,7 @@ vmlinux_link()
 	${ld} ${ldflags} -o ${output}					\
 		${wl}--whole-archive ${objs} ${wl}--no-whole-archive	\
 		${wl}--start-group ${libs} ${wl}--end-group		\
-		$@ ${ldlibs}
+		${wl}-Map=.tmp_vmlinux.map $@ ${ldlibs}
 }
 
 # generate .BTF typeinfo from DWARF debuginfo
@@ -246,6 +246,19 @@ 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), $NF }
+	    /^Linker script and memory map/ { start = 1 }
+	    /^\.brk/ { exit(0) }
+	' .tmp_vmlinux.map | sort > .tmp_vmlinux.ranges
+
+	# get kallsyms options
 	if is_enabled CONFIG_KALLSYMS_ALL; then
 		kallsymopt="${kallsymopt} --all-symbols"
 	fi
-- 
2.35.0.260.gb82b153193.dirty