On Fri, Jul 28, 2023 at 8:34 PM Will Deacon <will@xxxxxxxxxx> wrote: > > Some symbols emitted in the readelf output but filtered from System.map > can confuse the 'faddr2line' symbol size calculation, resulting in the > erroneous rejection of valid offsets. This is especially prevalent when > building an arm64 kernel with CONFIG_CFI_CLANG=y, where most functions > are prefixed with a 32-bit data value in a '$d.n' section. For example: > > 447538: ffff800080014b80 548 FUNC GLOBAL DEFAULT 2 do_one_initcall > 104: ffff800080014c74 0 NOTYPE LOCAL DEFAULT 2 $x.73 > 106: ffff800080014d30 0 NOTYPE LOCAL DEFAULT 2 $x.75 > 111: ffff800080014da4 0 NOTYPE LOCAL DEFAULT 2 $d.78 > 112: ffff800080014da8 0 NOTYPE LOCAL DEFAULT 2 $x.79 > 36: ffff800080014de0 200 FUNC LOCAL DEFAULT 2 run_init_process > > Adding a warning to do_one_initcall() results in: > > | WARNING: CPU: 0 PID: 1 at init/main.c:1236 do_one_initcall+0xf4/0x260 > > Which 'faddr2line' refuses to accept: > > $ ./scripts/faddr2line vmlinux do_one_initcall+0xf4/0x260 > skipping do_one_initcall address at 0xffff800080014c74 due to size mismatch (0x260 != 0x224) > no match for do_one_initcall+0xf4/0x260 > > Filter out entries from readelf using the 'sysmap-ignored-syms.sed' > script used to construct System.map, so that the size of a symbol is > calculated as a delta to the next symbol present in ksymtab. I do not think this patch set is the right approach. I assume faddr2line is meant to work with both vmlinux and modules. A problem is that we have different filtering policies wrt kallsyms. scripts/mksysmap filters symbols in vmlinux, while kernel/module/kallsyms.c filters ones in modules. This patch tries to get aligned with the stacktrace of vmlinux, but that does not seem optimal to the stacktrace of modules. I have not checked the details, but I guess the module kallsyms filters less symbols. https://github.com/torvalds/linux/blob/v6.5-rc4/kernel/module/kallsyms.c#L288 I prefer filtering symbols in the intersection of vmlinux and modules. is_mapping_symbol() filters symbols you are addressing. > Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > Cc: John Stultz <jstultz@xxxxxxxxxx> > Signed-off-by: Will Deacon <will@xxxxxxxxxx> > --- > scripts/faddr2line | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/scripts/faddr2line b/scripts/faddr2line > index 62a3fa6f6f59..da734af90036 100755 > --- a/scripts/faddr2line > +++ b/scripts/faddr2line > @@ -64,6 +64,7 @@ else > UTIL_PREFIX=${CROSS_COMPILE:-} > fi > > +IGNORED_SYMS=$(dirname $0)/sysmap-ignored-syms.sed > READELF="${UTIL_PREFIX}readelf" > ADDR2LINE="${UTIL_PREFIX}addr2line" > AWK="awk" > @@ -185,7 +186,7 @@ __faddr2line() { > found=2 > break > fi > - done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2) > + done < <(${READELF} --symbols --wide $objfile | sed -f ${IGNORED_SYMS} -e 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2) > > if [[ $found = 0 ]]; then > warn "can't find symbol: sym_name: $sym_name sym_sec: $sym_sec sym_addr: $sym_addr sym_elf_size: $sym_elf_size" > -- > 2.41.0.487.g6d72f3e995-goog > -- Best Regards Masahiro Yamada
