1 2Valgrind-developer notes, re the MacOSX port 3~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4 5JRS 22 Mar 09: re these comments in m_libc* and m_debuglog: 6 7/* IMPORTANT: on Darwin it is essential to use the _nocancel versions 8 of syscalls rather than the vanilla version, if a _nocancel version 9 is available. See docs/internals/Darwin-notes.txt for the reason 10 why. */ 11 12when Valgrind does (for its own purposes, not for the client) 13read/write/open/close etc syscalls, it really is critical to use the 14_nocancel versions of syscalls rather than the vanilla versions. This 15holds throughout the entire code base: whenever V does a syscall for 16its own purposes, we must use the _nocancel version if it exists. 17This is of course most prevalent in m_libc* since all of our 18own-purpose (non-client) syscalls should get routed through there. 19 20Why? Because on Darwin, pthread cancellation is done within the 21kernel (unlike on Linux, iiuc). And read/write/open/close and a whole 22bunch of other syscalls to do with stream I/O are cancellation points. 23So what can happen is, client informs the kernel that a given thread 24is to be cancelled. Then at the next (eg) VG_(printf) call by that 25thread, which leads to a sys_write, the write syscall gets hit by the 26cancellation request, and is duly nuked by the kernel. Of course from 27the outside it looks as if the thread had mysteriously disappeared off 28the radar for no reason. 29 30In short, we need to use _nocancel versions in order to ensure that 31cancellation requests only take effect at the places where the client 32does a syscall, and not the places where Valgrind does syscalls. 33 34How observed: using the standard pipe-based implementation in 35coregrind/m_scheduler/sema.c, none/tests/pth_cancel1 would hang 36(compared to succeeding using native Darwin semaphores). And if the 37"pause()" call in said test is turned into a spin ("while (1) ;") then 38the entire Valgrind run mysteriously disappears, rather than spinning 39using native Darwin semaphores. 40 41Because the pipe-based semaphore intensively uses sys_read/sys_write, 42it is not surprising that it inadvertently was eating up cancellation 43requests directed to client threads. With abovementioned change in 44force the pipe-based semaphore appears to work correctly. 45 46 47 48Valgrind-developer notes, things removed from the original MacOSX port 49~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 50There was a broken debugstub implementation. It was removed over several 51commits: r9477, which removed most of it, and r9711, r9759, and r10012, 52which cleaned up remaining bits. 53 54There was machinery to read function names from Dwarf3 debug info. But we 55already read function names from the symbol tables, so this was duplicated 56functionality. Furthermore, a Darwin-specific hack was required in 57storage.c to choose between symbol table names vs. Dwarf3 names. So this 58machinery was removed in r10155. 59 60 61Valgrind-developer notes, todos re the MacOSX port 62~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 63 64* m_syswrap/syscall-amd64-darwin.S 65 - correct signal mask is not applied during syscall 66 - restart-labels are completely bogus 67 68* m_syswrap/syswrap-darwin.c: 69 - PRE(sys_posix_spawn) completely ignores signal issues, and 70 also ignores the file_actions argument 71 72* Cleanups: sort wrappers in syswrap-darwin.c and priv_syswrap-darwin.h 73 alphabetically. Also, some aren't properly implemented -- check and 74 print warnings 75 76* Cleanups: m_scheduler/sema.c: use pipe implementation 77 (but this apparently causes none/tests/pth_cancel1 to hang. 78 I have no idea why, despite quite some investigation). 79 80* Cleanups: m_debugstub: move to attic 81 82* syswrap-darwin.c: sys_{f,}chmod_extended: handling of ARG5 is way 83 wrong 84 85* Cleanups (Linux,AIX5): bogus launcher-path mangling logic in 86 PRE(sys_execve) 87 88* Cleanups (ALL PLATFORMS): m_signals.c: are the _MY_SIGRETURN 89 assembly stubs actually necessary for anything? I don't know. 90 91* Cleanups: check that changes to VG_(stat) and VG_(stat64) have 92 not broken 64-bit statting on 32-bit Linux 93 94* Cleanups: #if !HAVE_PROC in m_main (to do with /proc/<pid>/cmdline 95 96-------- 97 98m_main doesn't read symbols for the valgrind exe itself, which is 99annoying. On minimal investigation it seems that the executable isn't 100even listed by aspacem. This is very strange and not in accordance 101with the Linux or AIX ports. 102 103 104m_main: relatedly, Darwin version does not collect/give out 105initial debuginfo handles; hence ptrcheck won't work 106 107 108m_main: Darwin port relies on blocking out big sections of address 109space with mmap at startup. We know from history that this is a bad 110idea. (It's also really slow on 64-bit builds, taking 3--4 seconds.) 111Also, startup is not done on the interim startup stack -- why not? 112 113 114VG_(di_notify_mmap): Linux version is also used for Darwin, and 115contains some ifdeffery. Clean up. 116 117 118PRE(sys_fork), #ifdeffery 119 120 121syswrap-generic.c: VG_(init_preopened_fds) is #ifdefd for Darwin 122 123 124scheduler.c: #ifdeffery in VG_(get_thread_out_of_syscall) 125 126 127look at notes in coregrind/Makefile.am re Mach RPC interface 128definitions. See if we can get rid of any more stuff now that 129m_debugstub is gone. 130