On 2/26/19 9:59 PM, Hauke Mehrtens wrote:
> Hi Johannes,
>
> When I compile iw 5.0.1 with link time optimization for MIPS32r2 big
> endian all commands are removed, it looks like this:
> ------------------------------------------------------------------------
> root@OpenWrt:/# iw
> Usage: iw [options] command
> Options:
> --debug enable netlink debugging
> --version show version (5.0.1)
> Commands:
>
> Commands that use the netdev ('dev') can also be given the
> 'wdev' instead to identify the device.
>
> You can omit the 'phy' or 'dev' if the identification is unique,
> e.g. "iw wlan0 info" or "iw phy0 info". (Don't when scripting.)
>
> Do NOT screenscrape this tool, we don't consider its output stable.
>
> root@OpenWrt:/#
> ------------------------------------------------------------------------
>
> When I compile it without LTO it works like expected.
> This was seen in OpenWrt in the iw-full version and when I remove all
> the OpenWrt specific patches to iw. The iw-tiny version from OpenWrt
> works like expected. iw 4.14 also works in both versions.
>
> This was report to OpenWrt here:
> https://github.com/openwrt/openwrt/pull/1865
> http://lists.infradead.org/pipermail/openwrt-devel/2018-October/014220.html
>
> With GCC 8.2 this also happens with iw 4.14.
>
>
> The binary with lto is even bigger and they have the same number of
> functions starting with __cmd:
>
> $ ls -al iw-full-*
> -rwxr-xr-x 1 hauke hauke 180164 Feb 26 21:55 iw-full-lto
> -rwxr-xr-x 1 hauke hauke 179016 Feb 26 21:57 iw-full-wo-lto
> $ nm iw-full-lto |fgrep __cmd |wc
> 96 288 7259
> $ nm iw-full-wo-lto |fgrep __cmd |wc
> 96 288 7259
>
> Hauke
Paul Fertser did some further analysis of this problem and we can now
reproduce it also on normal x86 systems when the binary is compiled like
this:
CFLAGS=" -Os -flto" LDFLAGS=" -flto" make
-O3 or -Os and link time optimization is needed to see this problem.
With LTO the compiler randomly reorders the __section_* variables
including __section_set and __section_get and that leads to wrong offset
used to traverse the __cmd section.
Hauke
