From 4924df7977f97475c93709bd3119f3b83d84bc6a Mon Sep 17 00:00:00 2001 From: Gabriel Krisman Bertazi Date: Thu, 19 Dec 2013 17:01:49 -0200 Subject: [PATCH] Fix PR breakpoints/16297: catch syscall with syscall 0 Code rationale ============== by: Gabriel Krisman Bertazi This is a fix for bug 16297. The problem occurs when the user attempts to catch any syscall 0 (such as syscall read on Linux/x86_64). GDB was not able to catch the syscall and was missing the breakpoint. Now, breakpoint_hit_catch_syscall returns immediately when it finds the correct syscall number, avoiding a following check for the end of the search vector, that returns a no hit if the syscall number was zero. Testcase rationale ================== by: Sergio Durigan Junior This testcase is a little difficult to write. By doing a quick inspection at the Linux source, one can see that, in many targets, the syscall number 0 is restart_syscall, which is forbidden to be called from userspace. Therefore, on many targets, there's just no way to test this safely. My decision was to take the simpler route and just adds the "read" syscall on the default test. Its number on x86_64 is zero, which is "good enough" since many people here do their tests on x86_64 anyway and it is a popular architecture. However, there was another little gotcha. When using "read" passing 0 as the third parameter (i.e., asking it to read 0 bytes), current libc implementations could choose not to effectively call the syscall. Therefore, the best solution was to create a temporary pipe, write 1 byte into it, and then read this byte from it. gdb/ChangeLog 2013-12-19 Gabriel Krisman Bertazi PR breakpoints/16297 * breakpoint.c (breakpoint_hit_catch_syscall): Return immediately when expected syscall is hit. gdb/testsuite/ChangeLog 2013-12-19 Sergio Durigan Junior PR breakpoints/16297 * gdb.base/catch-syscall.c (read_syscall, pipe_syscall) (write_syscall): New variables. (main): Create a pipe, write 1 byte in it, and read 1 byte from it. * gdb.base/catch-syscall.exp (all_syscalls): Include "pipe, "write" and "read" syscalls. (fill_all_syscalls_numbers): Improve the way to obtain syscalls numbers. --- gdb/ChangeLog | 6 ++++++ gdb/breakpoint.c | 7 +++---- gdb/testsuite/ChangeLog | 12 ++++++++++++ gdb/testsuite/gdb.base/catch-syscall.c | 16 ++++++++++++++++ gdb/testsuite/gdb.base/catch-syscall.exp | 11 ++++++----- 5 files changed, 43 insertions(+), 9 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 374b8c5..2bae7ae 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,9 @@ +2013-12-19 Gabriel Krisman Bertazi + + PR breakpoints/16297 + * breakpoint.c (breakpoint_hit_catch_syscall): Return immediately + when expected syscall is hit. + 2013-12-19 Tom Tromey * ser-unix.c (hardwire_ops): New global. diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c index 589aa19..6a11ddf 100644 --- a/gdb/breakpoint.c +++ b/gdb/breakpoint.c @@ -8325,10 +8325,9 @@ breakpoint_hit_catch_syscall (const struct bp_location *bl, VEC_iterate (int, c->syscalls_to_be_caught, i, iter); i++) if (syscall_number == iter) - break; - /* Not the same. */ - if (!iter) - return 0; + return 1; + + return 0; } return 1; diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 3e1c756..97ad49b 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,15 @@ +2013-12-19 Sergio Durigan Junior + + PR breakpoints/16297 + * gdb.base/catch-syscall.c (read_syscall, pipe_syscall) + (write_syscall): New variables. + (main): Create a pipe, write 1 byte in it, and read 1 byte from + it. + * gdb.base/catch-syscall.exp (all_syscalls): Include "pipe, + "write" and "read" syscalls. + (fill_all_syscalls_numbers): Improve the way to obtain syscalls + numbers. + 2013-12-19 Keven Boell * gdb.fortran/module.exp: Completion matches fortran module diff --git a/gdb/testsuite/gdb.base/catch-syscall.c b/gdb/testsuite/gdb.base/catch-syscall.c index 8f94191..aa5727a 100644 --- a/gdb/testsuite/gdb.base/catch-syscall.c +++ b/gdb/testsuite/gdb.base/catch-syscall.c @@ -16,17 +16,33 @@ static int close_syscall = SYS_close; static int chroot_syscall = SYS_chroot; +/* GDB had a bug where it couldn't catch syscall number 0 (PR 16297). + In most GNU/Linux architectures, syscall number 0 is + restart_syscall, which can't be called from userspace. However, + the "read" syscall is zero on x86_64. */ +static int read_syscall = SYS_read; +static int pipe_syscall = SYS_pipe; +static int write_syscall = SYS_write; static int exit_group_syscall = SYS_exit_group; int main (void) { + int fd[2]; + char buf1[2] = "a"; + char buf2[2]; + /* A close() with a wrong argument. We are only interested in the syscall. */ close (-1); chroot ("."); + pipe (fd); + + write (fd[1], buf1, sizeof (buf1)); + read (fd[0], buf2, sizeof (buf2)); + /* The last syscall. Do not change this. */ _exit (0); } diff --git a/gdb/testsuite/gdb.base/catch-syscall.exp b/gdb/testsuite/gdb.base/catch-syscall.exp index fd7d2db..5925419 100644 --- a/gdb/testsuite/gdb.base/catch-syscall.exp +++ b/gdb/testsuite/gdb.base/catch-syscall.exp @@ -47,7 +47,7 @@ if { [prepare_for_testing ${testfile}.exp $testfile ${testfile}.c] } { # All (but the last) syscalls from the example code # They are ordered according to the file, so do not change this. -set all_syscalls { "close" "chroot" } +set all_syscalls { "close" "chroot" "pipe" "write" "read" } set all_syscalls_numbers { } # The last syscall (exit()) does not return, so @@ -392,11 +392,12 @@ proc do_syscall_tests_without_xml {} { # This procedure fills the vector "all_syscalls_numbers" with the proper # numbers for the used syscalls according to the architecture. proc fill_all_syscalls_numbers {} { - global all_syscalls_numbers last_syscall_number + global all_syscalls_numbers last_syscall_number all_syscalls + + foreach syscall $all_syscalls { + lappend all_syscalls_numbers [get_integer_valueof "${syscall}_syscall" -1] + } - set close_syscall [get_integer_valueof "close_syscall" -1] - set chroot_syscall [get_integer_valueof "chroot_syscall" -1] - set all_syscalls_numbers [list $close_syscall $chroot_syscall] set last_syscall_number [get_integer_valueof "exit_group_syscall" -1] } -- 2.7.4