1eb3991427
I recently stumbled on this code mentioning Linux kernel 2.6.25, and thought it could be time for some spring cleaning (newer GDBs probably don't need to supports 12-year old kernels). I then found that the "legacy" case is probably broken anyway, which gives an even better motivation for its removal. In short, this patch removes the configure checks that check if user_regs_struct contains the fs_base/gs_base fields and adjusts all uses of the HAVE_STRUCT_USER_REGS_STRUCT_{FS,GS}_BASE macros. The longer explanation/rationale follows. Apparently, Linux kernels since 2.6.25 (that's from 2008) have been reliably providing fs_base and gs_base as part of user_regs_struct. Commit df5d438e33d7 in the Linux kernel [1] seems related. This means that we can get these values by reading registers with PTRACE_GETREGS. Previously, these values were obtained using a separate PTRACE_ARCH_PRCTL ptrace call. First, I'm not even sure the configure check was really right in the first place. The user_regs_struct used by GDB comes from /usr/include/x86_64-linux-gnu/sys/user.h (or equivalent on other distros) and is provided by glibc. glibc has had the fs_base/gs_base fields in there for a very long time, at least since this commit from 2001 [2]. The Linux kernel also has its version of user_regs_struct, which I think was exported to user-space at some point. It included the fs_base/gs_base fields since at least this 2002 commit [3]. In any case, my conclusion is that the fields were there long before the aforementioned Linux kernel commit. The kernel commit didn't add these fields, it only made sure that they have reliable values when obtained with PTRACE_GETREGS. So, checking for the presence of the fs_base/gs_base fields in struct user_regs_struct doesn't sound like a good way of knowing if we can reliably get the fs_base/gs_base values from PTRACE_GETREGS. My guess is that if we were using that strategy on a < 2.6.25 kernel, things would not work correctly: - configure would find that the user_regs_struct has the fs_base/gs_base fields (which are probided by glibc anyway) - we would be reading the fs_base/gs_base values using PTRACE_GETREGS, for which the kernel would provide unreliable values Second, I have tried to see how things worked by forcing GDB to not use fs_base/gs_base from PTRACE_GETREGS (forcing it to use the "legacy" code, by configuring with ac_cv_member_struct_user_regs_struct_gs_base=no ac_cv_member_struct_user_regs_struct_fs_base=no Doing so breaks writing registers back to the inferior. For example, calling an inferior functions gives an internal error: (gdb) p malloc(10) /home/smarchi/src/binutils-gdb/gdb/i387-tdep.c:1408: internal-error: invalid i387 regnum 152 The relevant last frames where this error happens are: #8 0x0000563123d262fc in internal_error (file=0x563123e93fd8 "/home/smarchi/src/binutils-gdb/gdb/i387-tdep.c", line=1408, fmt=0x563123e94482 "invalid i387 regnum %d") at /home/smarchi/src/binutils-gdb/gdbsupport/errors.cc:55 #9 0x0000563123047d0d in i387_collect_xsave (regcache=0x5631269453f0, regnum=152, xsave=0x7ffd38402a20, gcore=0) at /home/smarchi/src/binutils-gdb/gdb/i387-tdep.c:1408 #10 0x0000563122c69e8a in amd64_collect_xsave (regcache=0x5631269453f0, regnum=152, xsave=0x7ffd38402a20, gcore=0) at /home/smarchi/src/binutils-gdb/gdb/amd64-tdep.c:3448 #11 0x0000563122c5e94c in amd64_linux_nat_target::store_registers (this=0x56312515fd10 <the_amd64_linux_nat_target>, regcache=0x5631269453f0, regnum=152) at /home/smarchi/src/binutils-gdb/gdb/amd64-linux-nat.c:335 #12 0x00005631234c8c80 in target_store_registers (regcache=0x5631269453f0, regno=152) at /home/smarchi/src/binutils-gdb/gdb/target.c:3485 #13 0x00005631232e8df7 in regcache::raw_write (this=0x5631269453f0, regnum=152, buf=0x56312759e468 "@\225\372\367\377\177") at /home/smarchi/src/binutils-gdb/gdb/regcache.c:765 #14 0x00005631232e8f0c in regcache::cooked_write (this=0x5631269453f0, regnum=152, buf=0x56312759e468 "@\225\372\367\377\177") at /home/smarchi/src/binutils-gdb/gdb/regcache.c:778 #15 0x00005631232e75ec in regcache::restore (this=0x5631269453f0, src=0x5631275eb130) at /home/smarchi/src/binutils-gdb/gdb/regcache.c:283 #16 0x0000563123083fc4 in infcall_suspend_state::restore (this=0x5631273ed930, gdbarch=0x56312718cf20, tp=0x5631270bca90, regcache=0x5631269453f0) at /home/smarchi/src/binutils-gdb/gdb/infrun.c:9103 #17 0x0000563123081eed in restore_infcall_suspend_state (inf_state=0x5631273ed930) at /home/smarchi/src/binutils-gdb/gdb/infrun.c:9151 The problem seems to be that amd64_linux_nat_target::store_registers calls amd64_native_gregset_supplies_p to know whether gregset provides fs_base. When !HAVE_STRUCT_USER_REGS_STRUCT_FS_BASE, amd64_native_gregset_supplies_p returns false. store_registers therefore assumes that it must be an "xstate" register. This is of course wrong, and that leads to the failed assertion when i387_collect_xsave doesn't recognize the register. amd64_linux_nat_target::store_registers could probably be fixed to handle this case, but I don't think it's worth it, given that it would only be to support very old kernels. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=df5d438e33d7fc914ba9b6e0d6b019a8966c5fcc [2] https://sourceware.org/git/?p=glibc.git;a=commit;h=c9cf6ddeebb7bb [3] https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=88e4bc32686ebd0b1111a94f93eba2d334241f68 gdb/ChangeLog: * configure.ac: Remove check for fs_base/gs_base in user_regs_struct. * configure: Re-generate. * config.in: Re-generate. * amd64-nat.c (amd64_native_gregset_reg_offset): Adjust. * amd64-linux-nat.c (amd64_linux_nat_target::fetch_registers, amd64_linux_nat_target::store_registers, ps_get_thread_area, ): Adjust. gdbserver/ChangeLog: * configure.ac: Remove check for fs_base/gs_base in user_regs_struct. * configure: Re-generate. * config.in: Re-generate. * linux-x86-low.cc (x86_64_regmap, x86_fill_gregset, x86_store_gregset): Adjust. |
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.dir-locals.el | ||
.gitattributes | ||
.gitignore | ||
acinclude.m4 | ||
aclocal.m4 | ||
ax.cc | ||
ax.h | ||
ChangeLog | ||
config.in | ||
configure | ||
configure.ac | ||
configure.srv | ||
debug.cc | ||
debug.h | ||
dll.cc | ||
dll.h | ||
fork-child.cc | ||
gdb_proc_service.h | ||
gdbreplay.cc | ||
gdbthread.h | ||
hostio-errno.cc | ||
hostio.cc | ||
hostio.h | ||
i387-fp.cc | ||
i387-fp.h | ||
inferiors.cc | ||
inferiors.h | ||
linux-aarch32-low.cc | ||
linux-aarch32-low.h | ||
linux-aarch32-tdesc.cc | ||
linux-aarch32-tdesc.h | ||
linux-aarch64-ipa.cc | ||
linux-aarch64-low.cc | ||
linux-aarch64-tdesc.cc | ||
linux-aarch64-tdesc.h | ||
linux-amd64-ipa.cc | ||
linux-arm-low.cc | ||
linux-arm-tdesc.cc | ||
linux-arm-tdesc.h | ||
linux-bfin-low.cc | ||
linux-cris-low.cc | ||
linux-crisv32-low.cc | ||
linux-i386-ipa.cc | ||
linux-ia64-low.cc | ||
linux-low.cc | ||
linux-low.h | ||
linux-m32r-low.cc | ||
linux-m68k-low.cc | ||
linux-mips-low.cc | ||
linux-nios2-low.cc | ||
linux-ppc-ipa.cc | ||
linux-ppc-low.cc | ||
linux-ppc-tdesc-init.h | ||
linux-riscv-low.cc | ||
linux-s390-ipa.cc | ||
linux-s390-low.cc | ||
linux-s390-tdesc.h | ||
linux-sh-low.cc | ||
linux-sparc-low.cc | ||
linux-tic6x-low.cc | ||
linux-tile-low.cc | ||
linux-x86-low.cc | ||
linux-x86-tdesc.cc | ||
linux-x86-tdesc.h | ||
linux-xtensa-low.cc | ||
lynx-i386-low.cc | ||
lynx-low.cc | ||
lynx-low.h | ||
lynx-ppc-low.cc | ||
Makefile.in | ||
mem-break.cc | ||
mem-break.h | ||
notif.cc | ||
notif.h | ||
nto-low.cc | ||
nto-low.h | ||
nto-x86-low.cc | ||
proc-service.cc | ||
proc-service.list | ||
README | ||
regcache.cc | ||
regcache.h | ||
remote-utils.cc | ||
remote-utils.h | ||
server.cc | ||
server.h | ||
symbol.cc | ||
target.cc | ||
target.h | ||
tdesc.cc | ||
tdesc.h | ||
thread-db.cc | ||
tracepoint.cc | ||
tracepoint.h | ||
utils.cc | ||
utils.h | ||
win32-arm-low.cc | ||
win32-i386-low.cc | ||
win32-low.cc | ||
win32-low.h | ||
wincecompat.cc | ||
wincecompat.h | ||
x86-low.cc | ||
x86-low.h | ||
x86-tdesc.h | ||
xtensa-xtregs.cc |
README for GDBserver & GDBreplay by Stu Grossman and Fred Fish Introduction: This is GDBserver, a remote server for Un*x-like systems. It can be used to control the execution of a program on a target system from a GDB on a different host. GDB and GDBserver communicate using the standard remote serial protocol implemented in remote.c, and various *-stub.c files. They communicate via either a serial line or a TCP connection. For more information about GDBserver, see the GDB manual. Usage (server (target) side): First, you need to have a copy of the program you want to debug put onto the target system. The program can be stripped to save space if needed, as GDBserver doesn't care about symbols. All symbol handling is taken care of by the GDB running on the host system. To use the server, you log on to the target system, and run the `gdbserver' program. You must tell it (a) how to communicate with GDB, (b) the name of your program, and (c) its arguments. The general syntax is: target> gdbserver COMM PROGRAM [ARGS ...] For example, using a serial port, you might say: target> gdbserver /dev/com1 emacs foo.txt This tells GDBserver to debug emacs with an argument of foo.txt, and to communicate with GDB via /dev/com1. GDBserver now waits patiently for the host GDB to communicate with it. To use a TCP connection, you could say: target> gdbserver host:2345 emacs foo.txt This says pretty much the same thing as the last example, except that we are going to communicate with the host GDB via TCP. The `host:2345' argument means that we are expecting to see a TCP connection from `host' to local TCP port 2345. (Currently, the `host' part is ignored.) You can choose any number you want for the port number as long as it does not conflict with any existing TCP ports on the target system. This same port number must be used in the host GDBs `target remote' command, which will be described shortly. Note that if you chose a port number that conflicts with another service, GDBserver will print an error message and exit. On some targets, GDBserver can also attach to running programs. This is accomplished via the --attach argument. The syntax is: target> gdbserver --attach COMM PID PID is the process ID of a currently running process. It isn't necessary to point GDBserver at a binary for the running process. Usage (host side): You need an unstripped copy of the target program on your host system, since GDB needs to examine it's symbol tables and such. Start up GDB as you normally would, with the target program as the first argument. (You may need to use the --baud option if the serial line is running at anything except 9600 baud.) Ie: `gdb TARGET-PROG', or `gdb --baud BAUD TARGET-PROG'. After that, the only new command you need to know about is `target remote'. It's argument is either a device name (usually a serial device, like `/dev/ttyb'), or a HOST:PORT descriptor. For example: (gdb) target remote /dev/ttyb communicates with the server via serial line /dev/ttyb, and: (gdb) target remote the-target:2345 communicates via a TCP connection to port 2345 on host `the-target', where you previously started up GDBserver with the same port number. Note that for TCP connections, you must start up GDBserver prior to using the `target remote' command, otherwise you may get an error that looks something like `Connection refused'. Building GDBserver: The supported targets as of November 2006 are: arm-*-linux* bfin-*-uclinux bfin-*-linux-uclibc crisv32-*-linux* cris-*-linux* i[34567]86-*-cygwin* i[34567]86-*-linux* i[34567]86-*-mingw* ia64-*-linux* m32r*-*-linux* m68*-*-linux* m68*-*-uclinux* mips*64*-*-linux* mips*-*-linux* powerpc[64]-*-linux* s390[x]-*-linux* sh-*-linux* spu*-*-* x86_64-*-linux* Building GDBserver for your host is very straightforward. If you build GDB natively on a host which GDBserver supports, it will be built automatically when you build GDB. You can also build just GDBserver: % mkdir obj % cd obj % path-to-toplevel-sources/configure --disable-gdb % make all-gdbserver (If you have a combined binutils+gdb tree, you may want to also disable other directories when configuring, e.g., binutils, gas, gold, gprof, and ld.) If you prefer to cross-compile to your target, then you can also build GDBserver that way. In a Bourne shell, for example: % export CC=your-cross-compiler % path-to-topevel-sources/configure your-target-name --disable-gdb % make Using GDBreplay: A special hacked down version of GDBserver can be used to replay remote debug log files created by GDB. Before using the GDB "target" command to initiate a remote debug session, use "set remotelogfile <filename>" to tell GDB that you want to make a recording of the serial or tcp session. Note that when replaying the session, GDB communicates with GDBreplay via tcp, regardless of whether the original session was via a serial link or tcp. Once you are done with the remote debug session, start GDBreplay and tell it the name of the log file and the host and port number that GDB should connect to (typically the same as the host running GDB): $ gdbreplay logfile host:port Then start GDB (preferably in a different screen or window) and use the "target" command to connect to GDBreplay: (gdb) target remote host:port Repeat the same sequence of user commands to GDB that you gave in the original debug session. GDB should not be able to tell that it is talking to GDBreplay rather than a real target, all other things being equal. Note that GDBreplay echos the command lines to stderr, as well as the contents of the packets it sends and receives. The last command echoed by GDBreplay is the next command that needs to be typed to GDB to continue the session in sync with the original session.