Hi! On Wed, 24 Feb 2016 23:46:36 +0100, I wrote: > On Sat, 19 Sep 2015 14:00:23 +0200, Samuel Thibault <samuel.thiba...@gnu.org> > wrote: > > On Linux, -p and -pg do not make gcc link against libc_p.a, only > > -profile does (as documented in r11246), and thus people expect -p > > (Yo, 20 years ago...)
Now looking at glibc code of a similar vintage. ;-) > In my understanding, the Hurd needs crt0.o for static linking, and crt1.o > for dynamic linking. Likewise, for -pg or -p, I would assume that we > still need gcrt0.o for static linking, and gcrt1.o for dynamic linking. > I'm now testing the following patch: [...] > ..., which results in the following spec changes: > [...] > *startfile: > -%{!shared: > %{pg|p|profile:gcrt0.o%s;pie:Scrt1.o%s;static:crt0.o%s;:crt1.o%s}} > crti.o%s %{static:crtbeginT.o%s;shared|pie:crtbeginS.o%s;:crtbegin.o%s} > +%{!shared: > %{pg|p|profile:%{static:gcrt0.o%s;:gcrt1.o%s};pie:Scrt1.o%s;static:crt0.o%s;:crt1.o%s}} > crti.o%s %{static:crtbeginT.o%s;shared|pie:crtbeginS.o%s;:crtbegin.o%s} According to the GCC testsuite, that seems alright: a bunch of UNSUPPORTED -> PASS progressions in gcc.sum. (But I have not yet done any manual testing with gprof and such.) I also see a handful of executions FAILs, the first of which I've now looked into. I'll work on getting a glibc build going, to patch this up, but posting my analysis already, in case anyone has any comments. (Roland?) $ gcc/xgcc -Bgcc/ ../trunk/gcc/testsuite/gcc.dg/20021014-1.c -O2 -p -o ./20021014-1.exe $ gdb -q 20021014-1.exe Reading symbols from 20021014-1.exe...done. (gdb) r Starting program: [...]/20021014-1.exe [New Thread 15527.5] [New Thread 15527.6] Program received signal SIGFPE, Arithmetic exception. 0x01173155 in fetch_samples () at ../sysdeps/mach/hurd/profil.c:164 164 ../sysdeps/mach/hurd/profil.c: No such file or directory. (gdb) bt #0 0x01173155 in fetch_samples () at ../sysdeps/mach/hurd/profil.c:164 #1 0x01173365 in __profil (sample_buffer=0x0, size=0, offset=0, scale=0) at ../sysdeps/mach/hurd/profil.c:126 #2 0x0117292d in __moncontrol (mode=0) at gmon.c:93 #3 0x01172b56 in _mcleanup () at gmon.c:425 #4 0x0109c617 in __run_exit_handlers (status=0, listp=0x122055c <__exit_funcs>, run_list_atexit=true) at exit.c:82 #5 0x0109c661 in exit (status=0) at exit.c:104 #6 0x080484cd in main () at ../trunk/gcc/testsuite/gcc.dg/20021014-1.c:24 That is the "special_profil_failure" in ../sysdeps/mach/hurd/profil.c:fetch_samples. (gdb) print special_profil_failure $1 = EMACH_RCV_INVALID_NAME [glibc]/sysdeps/mach/hurd/bits/errno.h: [...] /* Errors from <mach/message.h>. */ [...] EMACH_RCV_INVALID_NAME = 0x10004002, [...] [gnumach]/include/mach/message.h: [...] #define MACH_RCV_INVALID_NAME 0x10004002 /* Bogus name for receive port/port-set. */ [...] We do have a profile thread created: (gdb) print profile_thread $2 = 63 (gdb) info threads Id Target Id Frame 6 Thread 15527.6 profile_waiter () at ../sysdeps/mach/hurd/profil.c:183 5 Thread 15527.5 0x0105c92c in mach_msg_trap () at /build/glibc-GlHAly/glibc-2.21/build-tree/hurd-i386-libc/mach/mach_msg_trap.S:2 * 4 Thread 15527.4 0x01173155 in fetch_samples () at ../sysdeps/mach/hurd/profil.c:164 3 bogus thread id 3 Can't fetch registers from thread bogus thread id 3: No such thread ..., but it's not yet been scheduled for execution: (gdb) thread 6 [Switching to thread 6 (Thread 15527.6)] #0 profile_waiter () at ../sysdeps/mach/hurd/profil.c:183 183 in ../sysdeps/mach/hurd/profil.c (gdb) bt #0 profile_waiter () at ../sysdeps/mach/hurd/profil.c:183 Backtrace stopped: Cannot access memory at address 0x2285000 (gdb) disassemble Dump of assembler code for function profile_waiter: => 0x011731b0 <+0>: push %ebp 0x011731b1 <+1>: push %edi 0x011731b2 <+2>: push %esi 0x011731b3 <+3>: push %ebx 0x011731b4 <+4>: mov $0x1,%esi 0x011731b9 <+9>: call 0x11a06a9 <__x86.get_pc_thunk.bx> [...] That is, the profile thread has not actually began to execute, when the main thread already tears down the process. During that, the main thread talks to profil_reply_port -- but that one is (to be) set up by the profile thread, which has not yet happened: (gdb) print profil_reply_port $3 = 0 The scenario is not surprising: [gcc]/gcc/testsuite/gcc.dg/20021014-1.c is just a few lines of code. Should we move the initialization of profil_reply_port elsewhere, or be prepared for profil_reply_port to be MACH_PORT_NULL in sysdeps/mach/hurd/profil.c:fetch_samples (by returning early?), or not call fetch_samples from sysdeps/mach/hurd/profil.c:__profil if profil_reply_port is MACH_PORT_NULL, or make sure that we're always properly initialized by making sure that the profile thread is always scheduled to execute right after it's been created? As far as I can tell, we'd run into the same problem as discussed here, if profil (sysdeps/mach/hurd/profil.c:__profil) is called to disable sampling, but it has never been called to enable sampling. Also, according to the man page, profil (sysdeps/mach/hurd/profil.c:__profil) should disable profiling if sample_buffer is NULL, not if scale is zero, as it's currently doing. As there are accesses to variables shared between different threads, should these be re-written to use GCC's atomic/sync load/store builtins with appropriate semantics? These days, do we still need the threadvar-avoidance magic, the "special RPC stubs", and the "special_profil_failure"? Grüße Thomas
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