kbuild: add CONFIG_VMLINUX_MAP expert option

It can be quite useful to have ld emit a link map file, in order to
debug or verify that special sections end up where they are supposed
to, and to see what LD_DEAD_CODE_DATA_ELIMINATION manages to get rid
of.

The only reason I'm not just adding this unconditionally is that the
.map file can be rather large (several MB), and that's a waste of
space when one isn't interested in these things. Also make it depend
on CONFIG_EXPERT.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

diff --git a/.gitignore b/.gitignore
index 3af6627..3adea59 100644 (file)
--- a/.gitignore
+++ b/.gitignore
@@ -59,6 +59,7 @@ modules.order
 /linux
 /vmlinux
 /vmlinux.32
+/vmlinux.map
 /vmlinux.symvers
 /vmlinux-gdb.py
 /vmlinuz

diff --git a/Documentation/dontdiff b/Documentation/dontdiff
index e361fc9..ac42ad8 100644 (file)
--- a/Documentation/dontdiff
+++ b/Documentation/dontdiff
@@ -252,6 +252,7 @@ vmlinux-*
 vmlinux.aout
 vmlinux.bin.all
 vmlinux.lds
+vmlinux.map
 vmlinux.symvers
 vmlinuz
 voffset.h

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2779c29..b479ae6 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -449,6 +449,16 @@ config VMLINUX_VALIDATION
        depends on STACK_VALIDATION && DEBUG_ENTRY && !PARAVIRT
        default y
 
+config VMLINUX_MAP
+       bool "Generate vmlinux.map file when linking"
+       depends on EXPERT
+       help
+         Selecting this option will pass "-Map=vmlinux.map" to ld
+         when linking vmlinux. That file can be useful for verifying
+         and debugging magic section games, and for seeing which
+         pieces of code get eliminated with
+         CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.
+
 config DEBUG_FORCE_WEAK_PER_CPU
        bool "Force weak per-cpu definitions"
        depends on DEBUG_KERNEL

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 3b261b0..855fd4e 100755 (executable)
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -155,6 +155,7 @@ vmlinux_link()
        local output=${1}
        local objects
        local strip_debug
+       local map_option
 
        info LD ${output}
 
@@ -166,6 +167,10 @@ vmlinux_link()
                strip_debug=-Wl,--strip-debug
        fi
 
+       if [ -n "${CONFIG_VMLINUX_MAP}" ]; then
+               map_option="-Map=${output}.map"
+       fi
+
        if [ "${SRCARCH}" != "um" ]; then
                if [ -n "${CONFIG_LTO_CLANG}" ]; then
                        # Use vmlinux.o instead of performing the slow LTO
@@ -187,6 +192,7 @@ vmlinux_link()
                ${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux}      \
                        ${strip_debug#-Wl,}                     \
                        -o ${output}                            \
+                       ${map_option}                           \
                        -T ${lds} ${objects}
        else
                objects="-Wl,--whole-archive                    \
@@ -200,6 +206,7 @@ vmlinux_link()
                ${CC} ${CFLAGS_vmlinux}                         \
                        ${strip_debug}                          \
                        -o ${output}                            \
+                       ${map_option:+-Wl,${map_option}}        \
                        -Wl,-T,${lds}                           \
                        ${objects}                              \
                        -lutil -lrt -lpthread
@@ -303,6 +310,7 @@ cleanup()
        rm -f .tmp_vmlinux*
        rm -f System.map
        rm -f vmlinux
+       rm -f vmlinux.map
        rm -f vmlinux.o
 }