Now bionic

Kalle has posted a rebased version of my SDIO patches on top of the latest wireless-testing. I’ve done a little bit of testing with it — the driver starts up and loads fine, but once the interface goes down, it’s busted:

<6>[ 980.884302] wl1251_sdio mmc0:0001:1: firmware: requesting wl1251-fw.bin
<6>[ 981.036448] wl1251_sdio mmc0:0001:1: firmware: requesting wl1251-nvs.bin
<3>[ 981.045449] init: untracked pid 354 exited
<3>[ 981.074408] init: untracked pid 355 exited
<7>[ 981.331853] wl1251: 151 tx blocks at 0x3b788, 35 rx blocks at 0x3a780
<7>[ 981.339300] wl1251: firmware booted (Rev
<7>[ 984.702740] wlan0: direct probe to AP 00:1a:70:da:a9:cd (try 1)
<7>[ 984.901621] wlan0: direct probe to AP 00:1a:70:da:a9:cd (try 2)
<7>[ 985.101583] wlan0: direct probe to AP 00:1a:70:da:a9:cd (try 3)
<7>[ 985.301617] wlan0: direct probe to AP 00:1a:70:da:a9:cd timed out
<7>[ 1024.802837] wl1251: down
<3>[ 1044.856640] init: untracked pid 358 exited
<3>[ 1050.033886] mmc0: Data timeout
<3>[ 1050.037701] wl1251: ERROR sdio write failed (-110)
<3>[ 1051.045674] mmc0: Data timeout
<3>[ 1051.049519] wl1251: ERROR sdio write failed (-110)
<3>[ 1052.057673] mmc0: Data timeout
<3>[ 1052.061518] wl1251: ERROR sdio write failed (-110)

Exploring this further turned into a rather long yak shaving session because I wanted to get iw on the phone to do more manual tests, and I wanted to link it dynamically against bionic, the Android’s fork of a BSD libc. Here were a few interesting discoveries found along the way:

$ ./iw
iw: not found

Right away, I intuited this was a problem finding, but I was setting LD_LIBRARY_PATH. So I looked at the bionic linker source to find:

/* TODO: Need to add support for initializing the so search path with
* LD_LIBRARY_PATH env variable for non-setuid programs. */

So had to go into the hard-coded library search path of /system/lib. That alone didn’t help, however. I eventually remembered that dynamically linked executables include the name of the dynamic linker in ELF headers, and on Android this is called “/system/bin/linker” instead of “/usr/lib/” After fixing that (-Wl,-dynamic-linker,/system/bin/linker), the program just SEGVed at startup, so I added Android linker scripts and other random crap to the linker command line (much of it furnished by the very cool agcc wrapper script).

# ./iw
Usage: ./iw [options] command
--debug enable netlink debugging
--version show version (0.9.14-2-g5286851)

Almost there, but no available commands? A glance at the iw source revealed that iw sticks all that stuff into an ELF section which mostly disappears when you link with –gc-sections. So with that exorcised from my linker command line, I finally have a functioning Android iw that is dynamically linked against bionic libc and my own cross-compiled libnl.

One wonders if the pain of bionic is worth its benefits, unless a benefit was curing ennui: “I’m bored, let’s write our own libc!” Anyway, I should be able to produce the various wireless tools natively compiled for Android in short order now. After that I’ll pop my Android TODO stack to the task, “make it easier to build custom images in my build environment.” I’d like to customize the filesystem images to have all of these utilities and relevant drivers in the normal places rather than hanging out in weird locations on the sdcard.