Re: [PATCH] libbpf: fix readelf output parsing on powerpc with recent binutils

On Wed, Dec 11, 2019 at 09:33:53AM -0600, Justin Forbes wrote:

quoted

On Tue, Dec 10, 2019 at 4:26 PM Thadeu Lima de Souza Cascardo
[off-list ref] wrote:

quoted

On Tue, Dec 10, 2019 at 12:58:33PM -0600, Justin Forbes wrote:

quoted

On Mon, Dec 2, 2019 at 3:37 AM Daniel Borkmann [off-list ref] wrote:

quoted

On Mon, Dec 02, 2019 at 04:53:26PM +1100, Michael Ellerman wrote:

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Aurelien Jarno [off-list ref] writes:

quoted

On powerpc with recent versions of binutils, readelf outputs an extra
field when dumping the symbols of an object file. For example:

    35: 0000000000000838    96 FUNC    LOCAL  DEFAULT [<localentry>: 8]     1 btf_is_struct

The extra "[<localentry>: 8]" prevents the GLOBAL_SYM_COUNT variable to
be computed correctly and causes the checkabi target to fail.

Fix that by looking for the symbol name in the last field instead of the
8th one. This way it should also cope with future extra fields.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 tools/lib/bpf/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Thanks for fixing that, it's been on my very long list of test failures
for a while.

Tested-by: Michael Ellerman <mpe@ellerman.id.au>

Looks good & also continues to work on x86. Applied, thanks!

This actually seems to break horribly on PPC64le with binutils 2.33.1
resulting in:
Warning: Num of global symbols in sharedobjs/libbpf-in.o (32) does NOT
match with num of versioned symbols in libbpf.so (184). Please make
sure all LIBBPF_API symbols are versioned in libbpf.map.

This is the only arch that fails, with x86/arm/aarch64/s390 all
building fine.  Reverting this patch allows successful build across
all arches.

Justin

Well, I ended up debugging this same issue and had the same fix as Jarno's when
I noticed his fix was already applied.

I just installed a system with the latest binutils, 2.33.1, and it still breaks
without such fix. Can you tell what is the output of the following command on
your system?

readelf -s --wide tools/lib/bpf/sharedobjs/libbpf-in.o | cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' | awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $0}'

readelf -s --wide tools/lib/bpf/sharedobjs/libbpf-in.o | cut -d "@"
-f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' | awk '/GLOBAL/ && /DEFAULT/ &&
!/UND/ {print $0}'
   373: 00000000000141bc  1376 FUNC    GLOBAL DEFAULT    1
libbpf_num_possible_cpus [<localentry>: 8]
   375: 000000000001869c   176 FUNC    GLOBAL DEFAULT    1 btf__free
[<localentry>: 8]

[...]

This is a patch on binutils carried by Fedora:

https://src.fedoraproject.org/rpms/binutils/c/b8265c46f7ddae23a792ee8306fbaaeacba83bf8

" b8265c Have readelf display extra symbol information at the end of the line. "

It has the following comment:

# FIXME:    The proper fix would be to update the scripts that are expecting
#           a fixed output from readelf.  But it seems that some of them are
#           no longer being maintained.

This commit is from 2017, had it been on binutils upstream, maybe the situation
right now would be different.

Honestly, it seems the best way out is to filter the other information in the
libbpf Makefile.

Does the following patch work for you?

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 56ce6292071b..e6f99484d7d5 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile

@@ -145,6 +145,7 @@ PC_FILE             := $(addprefix $(OUTPUT),$(PC_FILE))

 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/ {print $$8}' | \
                           sort -u | wc -l)
 VERSIONED_SYM_COUNT = $(shell readelf -s --wide $(OUTPUT)libbpf.so | \

@@ -217,6 +218,7 @@ check_abi: $(OUTPUT)libbpf.so
                     "versioned in $(VERSION_SCRIPT)." >&2;              \
                readelf -s --wide $(OUTPUT)libbpf-in.o |                 \
                    cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' |   \
+                   sed 's/\[.*\]//' |                                   \
                    awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$8}'|   \
                    sort -u > $(OUTPUT)libbpf_global_syms.tmp;           \
                readelf -s --wide $(OUTPUT)libbpf.so |                   \