Re: [PATCH elfutils 2/2] [tests] parse inode in /proc/pid/maps correctly in run-backtrace-data.sh

[Mark Wielaard <mark@klomp.org>]

On Fri, Jan 25, 2019 at 01:20:09PM -0800, Yonghong Song wrote:
> The backtrace-data.c parsed the inode in /proc/pid/maps with
> format "%*x".
> This caused failure if inode is big. For example,
>   7f269223d000-7f269226b000 r-xp 00000000 00:50 10224326387095067468       /home/...

I have a bit of trouble replicating this (with a simple sscanf).
How exactly does it fail?

> The correct format should be "%*lu" to reflect inode "unsigned long" type.
> But that caused the following compilation error.
>   acktrace-data.c: In function ‘maps_lookup’:
>   backtrace-data.c:109:22: error: use of assignment suppression and length modifier
>   together in gnu_scanf format [-Werror=format=]
>        i = fscanf (f, "%lx-%lx %*s %lx %*x:%*x %*lu", &start, &end, &offset);

Not that it matters much, since we are really ignoring the rest of the
line and this is just a test. But I do wonder why %*u doesn't work.
The warning says you cannot combine a length specifier with
a ignored format specifier. Which kind of makes sense given that the
length is for the variable to assign the value for, not the format.
So it seems $*u should do the trick. But since I haven't been able
to make the original fail, I might be wrong.

Cheers,

Mark