Re: [PATCH] Revert "scripts/faddr2line: Check only two symbols when calculating symbol size"

From: Will Deacon
Date: Fri Aug 16 2024 - 08:51:00 EST


On Mon, Aug 12, 2024 at 11:01:20PM +0000, Carlos Llamas wrote:
> This reverts commit c02904f05ff805d6c0631634d5751ebd338f75ec.
>
> Such commit assumed that only two symbols are relevant for the symbol
> size calculation. However, this can lead to an incorrect symbol size
> calculation when there are mapping symbols emitted by readelf.
>
> For instance, when feeding 'update_irq_load_avg+0x1c/0x1c4', faddr2line
> might need to processes the following readelf lines:
>
> 784284: ffffffc0081cca30 428 FUNC GLOBAL DEFAULT 2 update_irq_load_avg
> 87319: ffffffc0081ccb0c 0 NOTYPE LOCAL DEFAULT 2 $x.62522
> 87321: ffffffc0081ccbdc 0 NOTYPE LOCAL DEFAULT 2 $x.62524
> 87323: ffffffc0081ccbe0 0 NOTYPE LOCAL DEFAULT 2 $x.62526
> 87325: ffffffc0081ccbe4 0 NOTYPE LOCAL DEFAULT 2 $x.62528
> 87327: ffffffc0081ccbe8 0 NOTYPE LOCAL DEFAULT 2 $x.62530
> 87329: ffffffc0081ccbec 0 NOTYPE LOCAL DEFAULT 2 $x.62532
> 87331: ffffffc0081ccbf0 0 NOTYPE LOCAL DEFAULT 2 $x.62534
> 87332: ffffffc0081ccbf4 0 NOTYPE LOCAL DEFAULT 2 $x.62535
> 783403: ffffffc0081ccbf4 424 FUNC GLOBAL DEFAULT 2 sched_pelt_multiplier
>
> The symbol size of 'update_irq_load_avg' should be calculated with the
> address of 'sched_pelt_multiplier', after skipping the mapping symbols
> seen in between. However, the offending commit cuts the list short and
> faddr2line incorrectly assumes 'update_irq_load_avg' is the last symbol
> in the section, resulting in:
>
> $ scripts/faddr2line vmlinux update_irq_load_avg+0x1c/0x1c4
> skipping update_irq_load_avg address at 0xffffffc0081cca4c due to size mismatch (0x1c4 != 0x3ff9a59988)
> no match for update_irq_load_avg+0x1c/0x1c4
>
> After reverting the commit the issue is resolved:
>
> $ scripts/faddr2line vmlinux update_irq_load_avg+0x1c/0x1c4
> update_irq_load_avg+0x1c/0x1c4:
> cpu_of at kernel/sched/sched.h:1109
> (inlined by) update_irq_load_avg at kernel/sched/pelt.c:481
>
> Cc: Brian Johannesmeyer <bjohannesmeyer@xxxxxxxxx>
> Cc: John Stultz <jstultz@xxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
> ---
> scripts/faddr2line | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Will Deacon <will@xxxxxxxxxx>

I'm assuming that Josh will pick this up.

Cheers,

Will