On 10/07/2026 23:29, Ihor Solodrai wrote:
On 5/18/26 2:03 AM, James Clark wrote:
Documentation/kbuild/llvm.rst mentions that readelf is included in the
LLVM toolchain, but it's not currently included in this block.
Add it so that LLVM=... options also apply to readelf. Users in tools/
were Perf which was hardcoding it, and another was the BPF makefile.
Both already include Makefile.include so convert them to use the new
variable.
It also didn't have the cross compile prefix, so either readelf didn't
mind opening cross binaries, or it wasn't working for cross builds.
I'm pretty sure it's the former. readelf/llvm-readelf are only used
libbpf makefile to read ELF symbol tables, which should be arch-independent.
We've been cross-compiling the kernel (and libbpf) on BPF CI for a
long time. So the unprefixed readelf is already working, and adding
I think "working" isn't technically correct when you take into account
the documented behavior of the versioned LLVM= option [1]. You would get
one version of the toolchain used for some of the build and a different
version used here. That's what caused the build failure in Perf that
resulted in the tidyup, because they're not always compatible.
[1]: Documentation/kbuild/llvm.rst
the $(CROSS_COMPILE) prefix only adds a new requirement.
I don't think this change in tools/lib/bpf/Makefile is a good idea,
we could potentially break some environments. Even though hardcoded
readelf doesn't look nice.
IMO it's worth the risk for the cleanup, it also helps to stop
propagating it with future copy pastes.
Do you think it's likely that someone has CROSS_COMPILE set but doesn't
have that readelf installed? Installing gcc-aarch64-linux-gnu on
Debian/Ubuntu gives you aarch64-linux-gnu-readelf, so it would have to
be a unique setup to not have it.
It sounds like maybe you want this bpf makefile to explicitly use
'HOSTREADELF', if you're really sure it never requires arch specific
stuff? If we added that it would fit better with the rest of the
cleanup. But I think 'READELF' is less confusing and take the risk of
some build breakages.
Signed-off-by: James Clark <[email protected]>
---
tools/lib/bpf/Makefile | 8 ++++----
tools/perf/Makefile.perf | 1 -
tools/scripts/Makefile.include | 2 ++
3 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 168140f8e646..180dca9c57c8 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -114,12 +114,12 @@ PC_FILE := $(addprefix $(OUTPUT),$(PC_FILE))
TAGS_PROG := $(if $(shell which etags 2>/dev/null),etags,ctags)
-GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN_SHARED) | \
+GLOBAL_SYM_COUNT = $(shell $(READELF) -s --wide $(BPF_IN_SHARED) | \
cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' | \
sed 's/\[.*\]//' | \
awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print
$$NF}' | \
sort -u | wc -l)
-VERSIONED_SYM_COUNT = $(shell readelf --dyn-syms --wide $(OUTPUT)libbpf.so | \
+VERSIONED_SYM_COUNT = $(shell $(READELF) --dyn-syms --wide $(OUTPUT)libbpf.so
| \
sed 's/\[.*\]//' | \
awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print
$$NF}' | \
grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 | sort -u
| wc -l)
@@ -182,12 +182,12 @@ check_abi: $(OUTPUT)libbpf.so $(VERSION_SCRIPT)
"versioned symbols in $^ ($(VERSIONED_SYM_COUNT))." \
"Please make sure all LIBBPF_API symbols are" \
"versioned in $(VERSION_SCRIPT)." >&2; \
- readelf -s --wide $(BPF_IN_SHARED) | \
+ $(READELF) -s --wide $(BPF_IN_SHARED) | \
cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' | \
sed 's/\[.*\]//' | \
awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}'| \
sort -u > $(OUTPUT)libbpf_global_syms.tmp; \
- readelf --dyn-syms --wide $(OUTPUT)libbpf.so | \
+ $(READELF) --dyn-syms --wide $(OUTPUT)libbpf.so |
\
sed 's/\[.*\]//' | \
awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print $$NF}'| \
grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 | \
diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 0aba14f22a06..63276bf55856 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -215,7 +215,6 @@ FLEX ?= flex
BISON ?= bison
STRIP = strip
AWK = awk
-READELF ?= readelf
# include Makefile.config by default and rule out
# non-config cases
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index e81e5b479c56..380ad84ac51e 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -73,6 +73,7 @@ ifneq ($(LLVM),)
$(call allow-override,LLC,$(LLVM_PREFIX)llc$(LLVM_SUFFIX))
$(call allow-override,LLVM_CONFIG,$(LLVM_PREFIX)llvm-config$(LLVM_SUFFIX))
$(call allow-override,LLVM_OBJCOPY,$(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX))
+ $(call allow-override,READELF,$(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX))
else
# Allow setting various cross-compile vars or setting CROSS_COMPILE as a
prefix.
$(call allow-override,CC,$(CROSS_COMPILE)gcc)
@@ -80,6 +81,7 @@ else
$(call allow-override,LD,$(CROSS_COMPILE)ld)
$(call allow-override,CXX,$(CROSS_COMPILE)g++)
$(call allow-override,STRIP,$(CROSS_COMPILE)strip)
+ $(call allow-override,READELF,$(CROSS_COMPILE)readelf)
# Host versions aren't prefixed
$(call allow-override,HOSTAR,ar)
