From 1e64a66f72c79874016e78a4672b85cdeb506b9f Mon Sep 17 00:00:00 2001 From: Tom de Vries Date: Tue, 4 Jun 2024 09:30:03 +0000 Subject: [PATCH] [gdb/tdep] Fix gdb.base/watchpoint-running on {arm,ppc64le}-linux When running test-case gdb.base/watchpoint-running on ppc64le-linux, we get: ... (gdb) watch global_var^M warning: Error when detecting the debug register interface. \ Debug registers will be unavailable.^M Watchpoint 2: global_var^M (gdb) FAIL: $exp: all-stop: hardware: watch global_var FAIL: $exp: all-stop: hardware: watchpoint hit (timeout) ... The problem is that ppc_linux_dreg_interface::detect fails to detect the hardware watchpoint interface, because the calls to ptrace return with errno set to ESRCH. This is a feature of ptrace: if a call is done while the tracee is not ptrace-stopped, it returns ESRCH. Indeed, in the test-case "watch global_var" is executed while the inferior is running, and that triggers the first call to ppc_linux_dreg_interface::detect. And because the detection failure is cached, subsequent attempts at setting hardware watchpoints will also fail, even if the tracee is ptrace-stopped. Fix this by calling target_can_use_hardware_watchpoint from linux_init_ptrace_procfs, which is called from both: - linux_nat_target::post_attach, and - linux_nat_target::post_startup_inferior. By fixing this here, we also fix the same problem for arm-linux. Tested on ppc64le-linux and arm-linux. PR tdep/31834 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31834 PR tdep/31705 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31705 (cherry picked from commit bbc92bfbf25ad42548100e31e491ed3c32fbfa3e) --- gdb/linux-nat.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c index c8991cc3da4..47d74d27e11 100644 --- a/gdb/linux-nat.c +++ b/gdb/linux-nat.c @@ -385,6 +385,18 @@ linux_init_ptrace_procfs (pid_t pid, int attached) linux_ptrace_init_warnings (); linux_proc_init_warnings (); proc_mem_file_is_writable (); + + /* Some targets (for instance ppc and arm) may call ptrace to answer a + target_can_use_hardware_watchpoint query, and cache the result. However, + the ptrace call will fail with errno ESRCH if the tracee is not + ptrace-stopped, making the query fail. And if the caching mechanism does + not disregard an ESRCH result, all subsequent queries will also fail. + Call it now, where we known the tracee is ptrace-stopped. + + Other targets (for instance aarch64) do the relevant ptrace call and + caching in their implementation of post_attach and post_startup_inferior, + in which case this call is expected to have no effect. */ + target_can_use_hardware_watchpoint (bp_hardware_watchpoint, 1, 0); } linux_nat_target::~linux_nat_target () base-commit: a6800d9c8145f25001dd39afc3571e3350573e81 -- 2.35.3