Do you have too many git branches on the go at once? Here is the command to list them in order of last modification:
git for-each-ref --sort=-committerdate refs/heads
Do you have too many git branches on the go at once? Here is the command to list them in order of last modification:
git for-each-ref --sort=-committerdate refs/heads
This past few weeks I’ve been working on an Infinity client library. This is what GDB will use to execute notes it finds. It’s early days, but it executed its first note this morning so I thought I’d put something together so people can see what I’m doing. Here’s how to try it out:
tlsdump
example program needs it:
sudo yum install elfutils-libelf-devel # Fedora, RHEL, etc... sudo apt-get install libelf-dev # Debian, Ubuntu, etc...
git clone -b libi8x-0.0.1 https://github.com/gbenson/libi8x.git libi8x-0.0.1 cd libi8x-0.0.1 ./autogen.sh ./configure --enable-logging --enable-debug make
tlsdump
example program built:
bash$ ls -l examples/tlsdump -rwxr-xr-x. 1 gary gary 5540 Apr 20 12:52 examples/tlsdump
Yeah, there it is! (if it’s not there go back to step 0)
gcc -o tests/ifact tests/ifact.S tests/main.c
bash$ tests/ifact & [2] 8301 Hello world I'm 8301
tlsdump
example program with the test program’s PID as it’s argument:
$ examples/tlsdump 8301 0! = 1 1! = 1 2! = 2 3! = 6 4! = 24 5! = 120 6! = 720 7! = 5040 8! = 40320 9! = 362880 10! = 3628800 11! = 39916800 12! = 479001600
What just happened? The executable test/ifact
you built contains a single Infinity note, test::factorial(i)i
, the source for which is in tests/ifact.i8
. The tlsdump
example located the ifact
executable, loaded test::factorial(i)i
from it, and ran it a few times printing the result:
err = i8x_ctx_get_funcref (ctx, "test", "factorial", "i", "i", &fr); if (err != I8X_OK) error_i8x (ctx, err); err = i8x_xctx_new (ctx, 512, &xctx); if (err != I8X_OK) error_i8x (ctx, err); for (int i = 0; i < 13; i++) { union i8x_value args[1], rets[1]; args[0].i = i; err = i8x_xctx_call (xctx, fr, NULL, args, rets); if (err != I8X_OK) error_i8x (ctx, err); printf ("%d! = %d\n", i, rets[0].i); }
To see some debug output try this:
I8X_LOG=debug examples/tlsdump PID
Also try I8X_DEBUG=true
in addition to I8X_LOG=debug
to trace the bytecode as it executes.
I’m winding down for a month away from Infinity. The current status is that the language and note format changes for 0.0.2 are all done. You can get them with:
git clone https://github.com/gbenson/i8c.git
There’s also the beginnings of an Emacs major mode for i8 in there too. My glibc tree now has notes for td_ta_thr_iter
as well as td_ta_map_lwp2thr
. That’s two of the three hard ones done. Get them with:
git clone https://github.com/gbenson/glibc.git -b infinity2
FWIW td_thr_get_info
is just legwork and td_thr_tls_get_addr
is just a wrapper for td_thr_tlsbase
; td_thr_tlsbase
is the other hard note.
All notes have testcases with 100% bytecode coverage. I may add a flag for I8X to make not having 100% coverage a failure, and make glibc use it so nobody can commit notes with untested code.
The total note size so far is 720 bytes so I may still manage to get all five libpthread notes implemented in less than 1k:
Displaying notes found at file offset 0x00018f54 with length 0x000002d0: Owner Data size Description GNU 0x00000063 NT_GNU_INFINITY (inspection function) Signature: libpthread::__lookup_th_unique(i)ip GNU 0x00000088 NT_GNU_INFINITY (inspection function) Signature: libpthread::map_lwp2thr(i)ip GNU 0x000000cd NT_GNU_INFINITY (inspection function) Signature: libpthread::__iterate_thread_list(Fi(po)oipii)ii GNU 0x000000d2 NT_GNU_INFINITY (inspection function) Signature: libpthread::thr_iter(Fi(po)oiipi)i
To debug live processes on modern Linux GDB needs four libthread_db functions:
td_ta_map_lwp2thr
(required for initial attach)td_thr_get_info
(required for initial attach)td_thr_tls_get_addr
(not required for initial attach, but required for “p errno
” on regular executables)td_thr_tlsbase
(not required for initial attach, but required for “p errno
” for -static -pthread
executables)To debug a corefile on modern Linux GDB needs one more libthread_db function:
td_ta_thr_iter
GDB makes some other libthread_db calls too, but these are bookkeeping that won’t be required with the replacement. So, the order of work will be:
td_ta_thr_iter
too, and get that committed.dlmopen
.The first (non-bookkeeping) function GDB calls is td_ta_map_lwp2thr
and it’s a pig. If I can do td_ta_map_lwp2thr
I can do anything.
When you call it, td_ta_map_lwp2thr
has four ways it can proceed:
__pthread_initialize_minimal
has not gotten far enough we can’t rely on whatever’s in the thread registers. If this is the case, td_ta_map_lwp2thr
checks that the LWP is the initial thread and sets th->th_unique
to NULL. (Other bits of libthread_db spot this NULL and act accordingly.) td_ta_map_lwp2thr
decides whether __pthread_initialize_minimal
has gotten far enough by examining __stack_user.next
in the inferior. If it’s NULL then __pthread_initialize_minimal
has not gotten far enough.ta_howto_const_thread_area
architectures (x86_64, aarch64, arm)glibc/sysdeps/*/nptl/tls.h
has #define DB_THREAD_SELF CONST_THREAD_AREA(bits, value)
const uint32_t _thread_db_const_thread_area = value;
glibc/nptl_db/db_info.c
]:
td_ta_map_lwp2thr
will call ps_get_thread_area
with value
to set th->th_unique
.
ps_get_thread_area
(in GDB) does different things for different
architectures:
value
is a register number (FS or GS)ps_get_thread_area
returns the contents of that register.PTRACE_GET_THREAD_AREA, NULL
and subtracts value
from the result.PTRACE_GETREGSET, NT_ARM_TLS
and subtracts value
from the result.ta_howto_reg
architectures (ppc*, s390*)glibc/sysdeps/*/nptl/tls.h
has #define DB_THREAD_SELF REGISTER(bits, size, regofs, bias)...
const uint32_t _thread_db_register32[3] = {size, regofs, bias};
const uint32_t _thread_db_register64[3] = {size, regofs, bias};
glibc/nptl_db/db_info.c
]:
td_ta_map_lwp2thr
will:
and
to set th->unique
.
ta_howto_reg_thread_area
architectures (i386)glibc/sysdeps/*/nptl/tls.h
has #define DB_THREAD_SELF REGISTER_THREAD_AREA(bits, size, regofs, bias)...
const uint32_t _thread_db_register32_thread_area[3] = {size, regofs, bias};
const uint32_t _thread_db_register64_thread_area[3] = {size, regofs, bias};
glibc/nptl_db/db_info.c
]:
td_ta_map_lwp2thr
will:
ps_lgetregs
to get the inferior’s registers_td_fetch_value_local
)and
ps_get_thread_area
with that number to set th->unique
.
ps_get_thread_area
(in GDB) does different things for different
architectures:
PTRACE_GET_THREAD_AREA, VALUE
and returns the second element of the result.Cases 2, 3, and 4 will obviously be hardwired into the specific architecture’s libpthread. But… yeah.
If you’re debugging an application that loads thousands of shared libraries then be sure to read the LinkerInterface page on the GDB wiki.
I have a pair of set-top box PCs I’ve been using as always-on servers. I used them because they’re silent, but lately I’ve been thinking about power consumption. They were pretty good when I bought them in 2006 and 2008, but there’s much better stuff available now. I spent £60 on a Raspberry Pi and some supporting bits; given that it uses roughly a tenth the power of one of the set-top boxes it will have paid for itself in about two months.
While reorganising everything I also decommissioned an old Netgear switch which was likely costing £100 a year to run. Maybe it’s time you looked in your networking cupboard too!
I just committed a patch that makes GDB able to set breakpoints on inlined functions by name.
A couple of months ago I switched from the OpenJDK team to the GDB team. I’ll no doubt write something here about what I’m doing soon (ie within the next year or so) but in the meantime if you would like to apply for my old job at the awesomeness that is Red Hat then please click this link.
Andrew Hughes pointed out yesterday that the ARM interpreter and JIT are slated for removal in IcedTea6-1.11 unless someone steps up to maintain it. Currently there’s only one place where the all information about what’s required is collated—inside my head—so I thought I’d better write it up before I start forgetting. It’s entirely possible the interpreter will be removed, but it’s also possible that someone will end up trying to resurrect it months or years down the line. If you are that person and you are reading this then you owe me a beer ;)
The first change that broke the ARM code was the fix for PR icedtea/323, aka Sun bug 6939182. I described the required fix here:
“[In the ARM code] last_Java_sp
is set to the address of the top Zero frame wherever the frame anchor is set up. It needs changing such that last_Java_sp
is set to thread->zero_stack()->sp()
(and the new field last_Java_fp
gets set to what last_Java_sp
used to be set to).”
The second change that broke the ARM code was the fix for PR icedtea/484, aka Sun bug 6951784. I described the required fix here:
“I have had to change the calling convention within Zero and Shark. All method entries (the C function that executes the method) now return an integer which is the number of deoptimized frames they have left on the stack. Whenever a method is called it is now the caller’s responsibility to check whether frames have been deoptimized and reenter the interpreter if they have.”
The third change, currently in progress, reverts the last commit by the ARM code’s author, Ed Nevill: fix for fast bytecodes with ARM/Shark. This piece of code was accidentally incorporated in one of the webrevs when Zero was upstreamed, and isn’t conditionalised correctly. It can cause problems when the ARM code is not present, and there’s no neat fix. Given that the ARM code has been broken for five days shy of a year now I’ve asked for it to be removed from OpenJDK. This is Sun bug 7030207. If the ARM code is resurrected, this patch will require reinstating (with more specific conditionalisation please!)
The fourth change, currently in the future, is JSR 292. Explicit method handle stuff should just work–it’ll be handled by Zero–but the ARM interpreter and JIT will need updating to support three new instructions: invokedynamic
, fast_aldc
and fast_aldc_w
. The latter two are internal instructions, in case you wondered why you’d never heard of them before!
Ok, that is all.
I just discovered that the ARM-specific interpreter stuff that Ed Nevill wrote last year has a hack that disables it when run with -XX:+PrintCommandLineFlags
. I guess this is one problem when you have 6,000 14,000 lines of assembler nobody understands: you don’t know what secret weird shit is buried in there.