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.

Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: John Stultz <jstultz@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 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

On Tue, Jul 25, 2023 at 10:11:57PM +0100, Will Deacon wrote:
> @@ -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"

Looks good, though the outer loop has another readelf incantation:

	done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v fn=$sym_name '$4 == "FUNC" && $8 == fn')

It should probably have the same sed options?  Also it looks like it's
wrongly checking for FUNC.

-- 
Josh

On Tue, Jul 25, 2023 at 02:38:05PM -0700, Josh Poimboeuf wrote:
> On Tue, Jul 25, 2023 at 10:11:57PM +0100, Will Deacon wrote:
> > @@ -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: $sym_elf_size"
> 
> Looks good, though the outer loop has another readelf incantation:
> 
> 	done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v fn=$sym_name '$4 == "FUNC" && $8 == fn')
> 
> It should probably have the same sed options?

Hmm, I don't think it's needed there, is it? The awk expression has a
strict match on $sym_name, which is going to be something extracted from
a kernel log and therefore exists in kallsyms.

> Also it looks like it's wrongly checking for FUNC.

Yes, I agree that should be dropped for the reasons you gave before.

So I can spin a v3, with an extra patch to avoid checking against FUNC.

Will

On Thu, Jul 27, 2023 at 01:18:52PM +0100, Will Deacon wrote:
> On Tue, Jul 25, 2023 at 02:38:05PM -0700, Josh Poimboeuf wrote:
> > On Tue, Jul 25, 2023 at 10:11:57PM +0100, Will Deacon wrote:
> > > @@ -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: $sym_elf_size"
> > 
> > Looks good, though the outer loop has another readelf incantation:
> > 
> > 	done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v fn=$sym_name '$4 == "FUNC" && $8 == fn')
> > 
> > It should probably have the same sed options?
> 
> Hmm, I don't think it's needed there, is it? The awk expression has a
> strict match on $sym_name, which is going to be something extracted from
> a kernel log and therefore exists in kallsyms.

Yes, I think you're right.

> > Also it looks like it's wrongly checking for FUNC.
> 
> Yes, I agree that should be dropped for the reasons you gave before.
> 
> So I can spin a v3, with an extra patch to avoid checking against FUNC.

Sounds good, thanks!

-- 
Josh