On 10/20/2015 06:17 PM, Oleg Nesterov wrote: > Jan, Pedro, could you please confirm this won't break gdb? I tried > to look into gdb-7.1, and at first glance gdb uses __WCLONE only > because __WALL doesn't work on older kernels, iow it seems to me > that gdb actually wants __WALL so this change should be fine.
Right, gdb actually wants __WALL, but it doesn't use it to keep compatibility with kernels that predate it. gdb nowadays has an __WALL emulation waitpid wrapper (alternates __WCLONE+WNOHANG with 0+WNOHANG, blocks on sigsuspend/SIGCHLD): https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gdb/nat/linux-waitpid.c;h=cbcdd95afa9c664993542b0b3851e79fbae4e1df;hb=HEAD#l77 Though it's not used everywhere. Some older code in the ptrace backend open codes the "try __WCLONE, then try !__WCLONE." dance. Seems like __WALL was added in Linux 2.4; gdb could probably assume it's available nowadays... In any case, to make sure existing gdb binaries would still work with your kernel change, I ran GDB's testsuite with this: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ diff --git a/gdb/nat/linux-waitpid.c b/gdb/nat/linux-waitpid.c index cbcdd95..864ba2e 100644 --- a/gdb/nat/linux-waitpid.c +++ b/gdb/nat/linux-waitpid.c @@ -149,3 +149,17 @@ my_waitpid (int pid, int *status, int flags) errno = out_errno; return ret; } + +#include <dlfcn.h> + +pid_t +waitpid (pid_t pid, int *status, int options) +{ + static pid_t (*waitpid2) (pid_t pid, int *status, int options) = NULL; + + if (waitpid2 == NULL) + waitpid2 = dlsym (RTLD_NEXT, "waitpid"); + + options |= __WALL; + return waitpid2 (pid, status, options); +} ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ and got no regressions. So seems like all would be well from GDB's perspective. Thanks, Pedro Alves -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
