When trying to use BTF encoding for an apparently problematic kernel
file, pahole segfaults. As can be seen below [1], the problem is that we
are trying to dereference a NULL decoder.
Fix this by checking the return value of dwfl_getmodules which [2] will
return -1 on errors or an offset if one of the modules did not return
DWARF_CB_OK. (In this specific case, it was __cus__load_debug_types that
returned DWARF_CB_ABORT.)
[1]:
$ gdb -q --args ./pahole -J vmlinux-5.3.18-24.102-default.debug
Reading symbols from ./pahole...
(gdb) r
Starting program: /tmp/pahole/build/pahole -J vmlinux-5.3.18-24.102-default.debug
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7f4000e in gobuffer__size (gb=0x18) at /tmp/pahole/gobuffer.h:39
39 return gb->index;
(gdb) bt
(gdb) frame 1
1042 if (gobuffer__size(&encoder->percpu_secinfo) != 0)
(gdb) list
1037
1038 int btf_encoder__encode(struct btf_encoder *encoder)
1039 {
1040 int err;
1041
1042 if (gobuffer__size(&encoder->percpu_secinfo) != 0)
1043 btf_encoder__add_datasec(encoder, PERCPU_SECTION);
1044
1045 /* Empty file, nothing to do, so... done! */
1046 if (btf__get_nr_types(encoder->btf) == 0)
(gdb) print encoder
$1 = (struct btf_encoder *) 0x0
[2] https://sourceware.org/git/?p=elfutils.git;a=blob;f=libdwfl/libdwfl.h;h=f98f1d525d94bc7bcfc7c816890de5907ee4bd6d;hb=HEAD#l200
Signed-off-by: Kornilios Kourtis <kornilios@isovalent.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Link: http://lore.kernel.org/lkml/20220316132338.3226871-1-kkourt@kkourt.io
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Build instructions:
1. install cmake
2. mkdir build
3. cd build
4. cmake -D__LIB=lib ..
5. make install
cmake Options:
-DBUILD_SHARED_LIBS
By default SHARED libraries are created and applications are linked to it.
Use -DBUILD_SHARED_LIBS=OFF while invoking cmake to create STATIC libraries
and link applications to it.
Ex. cmake -D__LIB=lib -DBUILD_SHARED_LIBS=OFF ..
-DCMAKE_INSTALL_PREFIX
Default is to install to /usr/local, use -DCMAKE_INSTALL_PREFIX=
when invoking cmake to specify another install location.
Known to work scenarios:
Mandriva Cooker:
cmake 2.4.5-1mdv2007.1
libelfutils1-devel 0.123-1mdv2007.1
Debian Unstable:
cmake 2.4.5-1
libdw-dev 0.123-2
Fedora Core 6:
cmake 2.4.5-2.fc6
elfutils-devel 0.126-1.fc6
f952a6f69f