On Fri, Jul 28, 2023 at 4:34 AM 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 Sami, Should we change the llvm-ir linkage type for these symbols from `internal` to `private`? https://llvm.org/docs/LangRef.html#linkage-types Then they would not appear in the symbol table. At first, I thought other modules might need to directly reference this data, but with the local binding, I don't think they can. > > 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. > > 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 > -- Thanks, ~Nick Desaulniers
